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Nest Predation (nest + predation)

Distribution by Scientific Domains

Life Sciences	100%

Distribution within Life Sciences

Ornithology	28%
Conservation Science	19%
Ecology & Organismal Biology	11%

Terms modified by Nest Predation

nest predation rate

nest predation risk

Selected Abstracts

Patterns of Nest Predation on Artificial and Natural Nests in Forests

CONSERVATION BIOLOGY, Issue 2 2004
DAWN M. BURKE
ave de bosque; depredación de nidos; éxito de nidos; experimento de nidos artificiales; nidos naturales Abstract:,Artificial nest experiments have been used in an attempt to understand patterns of predation affecting natural nests. A growing body of literature suggests that neither relative rates nor patterns of predation are the same for artificial and natural nests. We studied nest predation and daily mortality rates and patterns at real and artificial ground and shrub nests to test the validity of artificial nest experiments. We monitored 1667 artificial and 344 natural nests, over seven trials, in three regions, across 58 sites in Ontario. We controlled for many of the factors thought to be responsible for previously reported differences between predation rates on natural and artificial nests. Although artificial nests in our study resembled natural nests, contained eggs of appropriate size, shape, and color of target bird species, and were placed in similar microhabitats as natural nests, the rates of predation on these nests did not parallel rates on natural nests for any region in terms of absolute rate or pattern. Predation rates on artificial nests did not vary between years, as they tended to for natural nests, and the magnitude of predation pressure on artificial ground nests compared with shrub nests did not show the same pattern as that on natural nests. In general, rates of predation on artificial nests were significantly higher than on natural nests. Our results suggest that conclusions derived from artificial nest studies may be unfounded. Given that many influential ideas in predation theory are based on results of artificial nest experiments, it may be time to redo these experiments with natural nests. Resumen:,Se han utilizado experimentos con nidos artificiales con la intención de entender los patrones de depredación que afectan a los nidos naturales. La bibliografía sugiere que ni las tasas relativas ni los patrones de depredación son iguales para nidos artificiales y naturales. Estudiamos las tasas y patrones de depredación de nidos y de mortalidad diaria en nidos reales y artificiales sobre el suelo y en matorrales para probar la validez de los experimentos con nidos artificiales. Monitoreamos 1667 nidos artificiales y 344 nidos naturales, en siete pruebas, en tres regiones, en 58 sitios en Notario. Controlamos muchos de los factores que se piensa son responsables de diferencias entre tasas de depredación en nidos naturales y artificiales reportadas previamente. Aunque los nidos artificiales en nuestro estudio se asemejaron a nidos naturales, contenían huevos de tamaño, forma y color adecuados para la especie de ave y fueron colocados en microhábitats similares a los de nidos naturales, las tasas de depredación en estos nidos no fueron similares a las tasas en nidos naturales en ninguna región en términos de tasa o patrón absoluto. Las tasas de depredación en nidos artificiales no variaron de un año a otro, como fue la tendencia en nidos naturales, y la magnitud de la presión de depredación en nidos sobre el suelo comparada con nidos en arbustos no mostró el mismo patrón que la depredación en nidos naturales. Nuestros resultados sugieren que las conclusiones derivadas de estudios con nidos artificiales pueden ser infundadas. Debido a que muchas ideas influyentes en la teoría de la depredación se basan en los resultados de experimentos con nidos artificiales, puede haber llegado el momento de volver a realizar estos experimentos utilizando nidos naturales. [source]

Factors affecting nest predation on forest songbirds in North America

IBIS, Issue 2007
FRANK R. THOMPSON III
Nest predation is an important factor in the ecology of passerines and can be a large source of mortality for birds. I provide an overview of factors affecting nest predation of passerines in North America with the goal that it may provide some insight into the ecology and management of woodland birds in the United Kingdom. Although several factors influence productivity, nest success is perhaps the most widely measured demographic characteristic of open-cup-nesting birds, and nest predation is usually the largest cause of nest failure. The identity of predator species, and how their importance varies with habitat and landscape factors, must be known for managers and scientists to design effective conservation plans and place research on nest predation in the appropriate context. Recent studies using video surveillance have made significant contributions to our understanding of the relative importance of different predator taxa in North America. Spatial and temporal variation in nest predation can be better understood when landscapes are placed in a biogeographical context and local habitat and nest-site effects are placed in a landscape context. Low productivity resulting from high nest predation is one of several potential causes of bird population declines in North America and the UK. Although the ,forest fragmentation paradigm' from the eastern US may not apply directly to the UK, thinking about avian demographics from a multiscale perspective, and consideration of factors affecting nest predation with knowledge of the dominant predator species, may provide insight into population declines. [source]

Islands in a desert: breeding ecology of the African Reed Warbler Acrocephalus baeticatus in Namibia

IBIS, Issue 4 2001
CORINE M. EISING
The continental African Reed Warbler Acrocephalus baeticatus, like its relative the Seychelles Warbler Acrocephalus sechellensis, breeds in isolated patches. We studied the mating system of the African Reed Warbler to see whether this species, like the Seychelles Warbler, shows co-operative breeding. The African Reed Warbler is not polygynous. The majority breed monogamously (88%, n= 65), however in 12% of the territories three adult unrelated birds (mostly males) were observed participating in the brooding and feeding of nestlings, suggesting a polyandrous breeding system. Multilocus DNA fingerprinting revealed that the helping bird was unrelated to the pair birds. The percentage of nests with helpers was low compared to rates found in the Seychelles Warbler or Henderson Reed Warbler Acrocephalus vaughani taiti. This could be due to the scarcity of potential helpers or to the fact that, although limited, birds still had the opportunity to disperse within a meta-population structure in search of vacant territories. The presence of helpers was associated with increased hatching success due to lower predation rates, but not with increased fledging success. Another possible benefit of helping behaviour in this species could be improved predator detection and mobbing. Nest predation was high and warblers tended to build their nests in the highest, most dense reed patches available in their territory. There was no relation between habitat quality, measured as insect food availability, and the occurrence of helpers. [source]

Nest predators of Lance-tailed Manakins on Isla Boca Brava, Panamá

JOURNAL OF FIELD ORNITHOLOGY, Issue 2 2009
Jennifer L. Reidy
ABSTRACT Nest predation is often the primary cause of nest failure for passerines. Despite this, little is known about predation rates and the nest predators of birds in the tropics. I used video cameras to monitor seven Lance-tailed Manakin (Chiroxiphia lanceolata) nests on Isla Boca Brava, Panamá. One nest fledged young and six nests failed due to predation. I recorded five predation events involving four avian predators and one mammalian predator. Crested Oropendolas (Psarocolius decumanus) predated two nests and a Roadside Hawk (Buteo magnirostris) and a Black-chested Jay (Cyanocorax affinis) each predated one. The mammalian predator was a common opossum (Didelphis marsupialis). All avian predation was diurnal; the mammalian predation was nocturnal. My results suggest that tropical birds are subject to a diverse suite of nest predators, and that avian predators may be an important cause of nest failure at my study site. RESUMEN La depredación de nidos es usualmente la primera causa del fracaso de lo nidos de los paserinos. A pesar de esto, poco se conoce sobre la tasa de depredación y los depredadores de nidos de aves neotropicales. Yo use cámaras de video para monitorear siete nidos del Lance-tailed Manakins (Chiroxiphia lanceolata) en la isla Boca brava, Panamá. De un nido salieron polluelos y seis nidos fracasaron debido a la depredación. Yo documente cinco eventos de depredación de los cuales cuatro fueron por aves y uno por mamíferos. Crested Oropendolas (Psarocolius decumanus) depredo dos nidos y Roadside Hawk (Buteo magnirostris) y el Black-chested Jay (Cyanocorax affinis) depredaron uno cada uno. El depredador mamífero fue un marsupial común (Didelphis marsupialis). Todas las depredaciones de aves fueron diurnas y la del mamífero fue nocturna. Mis resultados sugieren que las aves neotropicales están sujetas a una diversa gama de depredadores de nidos y posiblemente la depredación por aves puede ser una causa importante del fracaso de las nidadas en mi lugar de estudio. [source]

Predators at bird nests in a northern hardwood forest in New Hampshire

JOURNAL OF FIELD ORNITHOLOGY, Issue 3 2006
David I. King
ABSTRACT Nest predation is the primary cause of nest failure in most passerine birds, and increases in nest predation associated with anthropogenic habitat disturbance are invoked as explanations for population declines of some bird species. In most cases, however, the identity of the nest predators is not known with certainty. We monitored active bird nests with infrared time-lapse video cameras to determine which nest predators were responsible for depredating bird nests in northern New Hampshire. We monitored 64 nests of 11 bird species during three breeding seasons, and identified seven species of predators during 14 predation events. In addition, we recorded two instances of birds defending nests from predators and, in both cases, these nests were ultimately lost to predation. These results contrast with other studies in terms of the relatively high proportion of nests depredated by raptors and mice, as well as the absence of any predation by snakes. The diverse suite of predators in this and other studies is likely to confound our understanding of patterns of nest predation relative to fragmentation and habitat structure. SINOPSIS La depredación de nidos es la causa principal del fracaso de anidamiento de muchos paserinos. El incremento en depredación ha sido asociado a disturbio antropogénico de habitat y considerado como la causa de la disminución poblacional de muchas especies de aves. En la mayoría de los casos, no se sabe a ciencia cierta quién es el depredador. Monitoreamos nidos activos con cámaras infrarojas de video que tomaban la acción en lapsos para determinar que depredadores eran responsables de la pérdida de nidos en el norte de New Hampshire. A lo largo de tres temporadas reproductivas monitoreamos 64 nidos, pertenecientes a 11 especies, e identificamos siete depredadores en 14 actos de depredación. Además, pudimos grabar dos casos en donde los aves defendieron sus nidos, aunque los nidos eventualmente fueron depredados posteriormente. Estos resultados contrastan con otros estudios en términos de la alta proporción de depredación por parte de rapaces y ratoncitos, y en la ausencia de depredación por parte de culebras. La diversidad de depredadores en este y otros estudios ampliará los conocimiento sobre los patrones de depredación en nidos, y su relación con la fragmentación y la estructura del hábitat. [source]

A predator's perspective of nest predation: predation by red squirrels is learned, not incidental

OIKOS, Issue 5 2010
Shawna A. Pelech
Nest predation has been used to explain aspects of avian ecology ranging from nest site selection to population declines. Many arguments rely on specific assumptions regarding how predators find nests, yet these predatory mechanisms remain largely untested. Here we combine artificial nest experiments with behavioural observations of individual red squirrels Tamiasciurus hudsonicus to differentiate between two common hypotheses: predation is incidental versus learned. Specifically, we tested: 1) whether nest survival could be explained solely by a squirrel's activity patterns or habitat use, as predicted if predation was incidental; or 2) if predation increased as a squirrel gained experience preying on a nest, as predicted if predation was learned. We also monitored squirrel activity after predation to test for evidence of two search mechanisms: area-restricted searching and use of microhabitat search images. Contrary to incidental predation and in support of learning, squirrels did not find nests faster in areas with high use (e.g. forest edges). Instead, survival of artificial nests was strongly related to a squirrel's prior experience preying on artificial nests. Experience reduced nest survival times by over half and increased predation rates by 150,200%. Squirrels returned to and doubled their activity at the site of a previously preyed on nest. However, neither area-restricted searching nor microhabitat search images can explain how squirrels located artificial nests more readily with experience. Instead, squirrels likely used cues associated with the nests or eggs themselves. Learning implies that squirrels could be increasingly effective predators as the density or profitability of nests increases. Our results add support to the view that nest predation is complex and broadly influenced (e.g. by predator experience, motivation), and is unlikely to be predicted consistently by simple relationships with predator activity, abundance or habitat. [source]

Does attraction to conspecifics explain the patch-size effect?

OIKOS, Issue 8 2009
An experimental test
Recent theory suggests that attraction to conspecifics during habitat selection can be one potential, yet untested, mechanism for animal sensitivity to habitat fragmentation. The least flycatcher Empidonax minimus, a highly territorial migratory bird, has previously been shown to be attracted to conspecifics and sensitive to patch size by avoiding small patches of riparian forest in Montana, USA. I used a large-scale field experiment in this region to test the conspecific attraction hypothesis for explaining sensitivity to patch size, and I supplemented this experiment by estimating whether vegetation structure, nest predation, or nest parasitism rates could better explain patterns of sensitivity to patch size. Vegetation structure did not vary consistently with patch size, based on a random sample of patches across 150,km of the Madison and Missouri Rivers, Montana. Nest predation and parasitism rates by brown-headed cowbirds Molothrus ater also did not vary with patch size during the experiment. However, when conspecific cues were simulated across a gradient of patch sizes, flycatchers settled in all patches , and their sensitivity to patch size vanished , providing strong support for the conspecific attraction hypothesis. These results provide the first experimental evidence that attraction to conspecifics can indeed help explain area sensitivity in nature and highlight how understanding the role of animal behavior in heterogeneous landscapes can aid in interpreting pressing conservation issues. [source]

Forest fragmentation relaxes natural nest predation in an Afromontane forest

ANIMAL CONSERVATION, Issue 4 2009
T. Spanhove
Abstract Nest predation is widely regarded as a major driver underlying the population dynamics of small forest birds. Following forest fragmentation and the subsequent invasion by species from non-forested landscape matrices, shifts in predator communities may increase nest predation near forest edges. However, effects of human-driven habitat change on nest predation have mainly been inferred from studies with artificial nests, despite being regarded as poor surrogates for natural ones. We studied variation in predation rates, and relationships with timing of breeding and characteristics of microhabitats and fragments, on natural white-starred robin Pogonocichla stellata nests during three consecutive breeding seasons (2004,2007) in a Kenyan fragmented cloud forest. More than 70% of all initiated nests were predated during each breeding season. Predation rates nearly quadrupled between the earliest and the latest nests within a single breeding season, increased with distance to the forest edge, and decreased with the edge-to-area ratio of forest fragments. These spatial relationships oppose the traditional perception of edge and fragmentation effects on nest predation, but are in line with results from artificial nest experiments in other East African forests. In case of inverse edge and fragmentation effects on nest predation, such as shown in this study, species that tolerate edges for breeding may be affected positively, rather than negatively, by forest fragmentation, while the opposite can be expected for species restricted to the forest interior. The possibility of inverse edge effects, and its conservation implications, should therefore be taken into account when drafting habitat restoration plans. [source]

Patterns of Nest Predation on Artificial and Natural Nests in Forests

Nest protection in mallards Anas platyrhynchos: untangling the role of crypsis and parental behaviour

FUNCTIONAL ECOLOGY, Issue 5 2008
J. Kreisinger
Summary 1The covering of clutches with nest material is generally considered to improve the thermal environment of developing embryos. Here we tested an alternative hypothesis: that this behaviour reduces the risk of clutch detection by predators and hence, fulfils a cryptic anti-predation function in a ground-nesting non-passerine bird, the mallard. In addition, we assess the anti-predation function of the direct presence of an incubating parent on the nest for the first time in a ground-nesting non-passerine bird. 2We compared predation rates of real mallard nests with two types of artificial clutches: (i) covered with nest material and (ii) uncovered. In addition, the cryptic effectiveness of nest material, female body presence, and uncovered clutch were assessed using a simulated search for nests on photographs by human volunteers. This allowed us to evaluate separately the impact of overall crypsis (covering of the clutch by nest material and colouration of the female feather) and the direct protective capacity of the incubating female. 3Our data demonstrate that in mallards, concealment of the clutch with nest material reduces the risk of nest predation. Although the incubating female seems to provide less effective crypsis to the nest than nest material alone, the presence of the female on the clutch enhanced nest survival, suggesting a significant anti-predation capacity of the incubating parent in this species. 4Contrary to some previous studies, the relative effects of crypsis and parental anti-predation behaviour on nest survival did not differ with respect to nest concealment by surrounding vegetation. [source]

Factors affecting nest predation on forest songbirds in North America

The functional significance of multiple nest-building in the Australian Reed Warbler Acrocephalus australis

IBIS, Issue 3 2006
MATHEW L. BERG
The vast majority of bird species build a nest in which to breed. Some species build more than one nest, but the function of most multiple nest-building remains unclear. Here we describe the unusual nest-building behaviour of the Australian Reed Warbler Acrocephalus australis, and test experimentally the hypotheses that multiple nest-building is related to individual condition or territory quality, and plays a role in mate assessment. Australian Reed Warblers built two types of nest structures: ,type I' nests, which were used for eggs and nestlings, and ,type II' nests, which were structurally distinct from type I nests, did not support eggs, nestlings or adults and were not essential for successful breeding. The number of type II nests built in each territory varied. Type II nests were only built before breeding had commenced in a territory and females were not observed participating in their construction, supporting a role in female mate choice. Birds provided with supplementary food built significantly more type II nests than control birds. However, supplementary-fed birds did not have greater pairing success, and the addition of further type II nests to territories did not increase the pairing rate or type II nest construction in those territories. There was no relationship between the presence of type II nests and either reproductive success or likelihood of nest predation. We discuss the implications of these results in light of previous suggestions regarding the function of multiple nest-building in birds. [source]

The recent declines of farmland bird populations in Britain: an appraisal of causal factors and conservation actions

IBIS, Issue 4 2004
Ian Newton
In this paper, the main aspects of agricultural intensification that have led to population declines in farmland birds over the past 50 years are reviewed, together with the current state of knowledge, and the effects of recent conservation actions. For each of 30 declining species, attention is focused on: (1) the external causes of population declines, (2) the demographic mechanisms and (3) experimental tests of proposed external causal factors, together with the outcome of (4) specific conservation measures and (5) agri-environment schemes. Although each species has responded individually to particular aspects of agricultural change, certain groups of species share common causal factors. For example, declines in the population levels of seed-eating birds have been driven primarily by herbicide use and the switch from spring-sown to autumn-sown cereals, both of which have massively reduced the food supplies of these birds. Their population declines have been associated with reduced survival rates and, in some species, also with reduced reproductive rates. In waders of damp grassland, population declines have been driven mainly by land drainage and the associated intensification of grassland management. This has led to reduced reproductive success, as a result of lowered food availability, together with increased disturbance and trampling by farm stock, and in some localities increased nest predation. The external causal factors of population decline are known (with varying degrees of certainty) for all 30 species considered, and the demographic causal factors are known (again with varying degrees of certainty) for 24 such species. In at least 19 species, proposed causal factors have been tested and confirmed by experiment or by local conservation action, and 12 species have been shown to benefit (in terms of locally increased breeding density) from options available in one or more agri-environment schemes. Four aspects of agricultural change have been the main drivers of bird population declines, each affecting a wide range of species, namely: (1) weed-control, mainly through herbicide use; (2) the change from spring-sown to autumn-sown cereal varieties, and the associated earlier ploughing of stubbles and earlier crop growth; (3) land drainage and associated intensification of grassland management; and (4) increased stocking densities, mainly of cattle in the lowlands and sheep in the uplands. These changes have reduced the amounts of habitat and/or food available to many species. Other changes, such as the removal of hedgerows and ,rough patches', have affected smaller numbers of species, as have changes in the timings of cultivations and harvests. Although at least eight species have shown recent increases in their national population levels, many others seem set to continue declining, or to remain at a much reduced level, unless some relevant aspect of agricultural practice is changed. [source]

Breeding biology and breeding success of the Lesser Grey Shrike Lanius minor in a stable and dense population

IBIS, Issue 2 2000
ANTON KRISTIN
The Lesser Grey Shrike Lanius minor is highly endangered throughout Europe, having declined markedly in abundance and range. Long-term changes in climate and agricultural practices have been identified as the main reasons for its decline. To determine which factors influence short-term changes in breeding success, we examined several aspects of its breeding biology. Our investigation revealed that our study area bears a large and stable population of this species. In 1996 and 1997, we recorded 84 and 77 breeding pairs in an area of 20 km2, with an average of 4.20 and 3.85 pairs/km2 respectively. Data on breeding density, clutch size and fledging success from 1989 to 1997 (excluding 1992) indicate a stable breeding population with a constant high breeding success. Reproductive success declined through the season, mainly through seasonal variation in clutch size rather than chick mortality. However, breeding success was generally high (69% and 79% of the nests produced chicks], with low hatching failure and few nest losses. The main cause of breeding failure was nest predation (at least 50% of nest losses), mainly by magpies (at least 66% of depredated nests). Although in this population the Lesser Grey Shrike tends to aggregate in clusters, breeding density had no obvious effect on breeding success and nest predation. [source]

Can selection on nest size from nest predation explain the latitudinal gradient in clutch size?

JOURNAL OF ANIMAL ECOLOGY, Issue 5 2010
Luis Biancucci
Summary 1.,Latitudinal variation in clutch sizes of birds is a well described, but poorly understood pattern. Many hypotheses have been proposed, but few have been experimentally tested, and none have been universally accepted by researchers. 2.,The nest size hypothesis posits that higher nest predation in the tropics favours selection for smaller nests and thereby constrains clutch size by shrinking available space for eggs and/or nestlings in the nest. We tested this hypothesis with an experiment in a tropical forest and a comparative study between temperate and tropical field sites. 3.,Specifically, we tested if: (i) predation increased with nest size; (ii) tropical birds had smaller nests controlled for body size; and (iii) clutch size was explained by nest size controlled for body size. 4.,Experimental swapping of nests of different sizes showed that nest predation increased with nest size in the tropical site. Moreover, nest predation rates were higher in species with larger nests in both sites. However, nest size, corrected for body mass and phylogeny, did not differ between sites and was not related to clutch size between sites. 5.,Hence, nest predation can exert selection on nest size as predicted by the hypothesis. Nest size increased with adult body mass, such that adult size might indirectly influence reproductive success through effects on nest size and nest predation risk. Ultimately, however, selection from nest predation on nest size does not explain the smaller clutch sizes typical of the tropics. [source]

Diet reconstruction and historic population dynamics in a threatened seabird

JOURNAL OF APPLIED ECOLOGY, Issue 4 2007
D. RYAN NORRIS
Summary 1For the overwhelming majority of species, we lack long-term information on the dynamics of populations. As a consequence, we face considerable uncertainty about how to discriminate among competing hypotheses of population decline and design conservation plans. 2The marbled murrelet Brachyramphus marmoratus is a small seabird that nests in coastal old-growth forest but feeds year-round in near-shore waters of the north-eastern Pacific. Although a decline in nesting habitat is the primary reason why marbled murrelets are listed as threatened in Canada, nest predation and food availability may also influence population abundance. To examine the hypothesis that murrelet populations are influenced by variation in diet quality, we analysed stable-carbon and -nitrogen isotopes in feathers of museum specimens collected in the Georgia Basin, British Columbia. 3Between 1889 and 1996, we found a decline in stable isotopic signatures that was approximately equal to a 62% drop in trophic feeding level. We also found that the estimated proportion of fish in murrelet diet was related closely to murrelet abundance over the past 40 years, as estimated from volunteer surveys. Using these isotopic data, we modelled population size as a function of variation in reproductive rate due to changes in diet quality and found that our model matched closely the 40-year field estimates. We then applied our 107-year isotopic record to the model to back-cast estimates of population growth rate to 1889. 4Our results suggest that, up to the 1950s, murrelet populations in the Georgia Basin were capable of growing and were probably limited by factors other than diet quality. After this period, however, our results imply that murrelets were often, but not solely, limited by diet quality. 5Synthesis and applications. Protecting nesting habitat may not be sufficient to rebuild populations of this highly secretive and threatened seabird and recovery might also require the restoration of marine habitat quality, as well as a better understanding of how ocean climate affects prey abundance and reproductive rate. Combined with contemporary demographic data, stable isotope analysis of historic samples provides a unique opportunity to reconstruct population histories for species where we lack long-term information. [source]

Investigator activities reduce nest predation in blackbirds Turdus merula

JOURNAL OF AVIAN BIOLOGY, Issue 2 2010
Juan Diego Ibáñez-Álamo
The effect of investigator perturbance has been traditionally considered detrimental for avian nesting success in terms of enhanced nest predation. This conclusion was however based on a taxonomically biased group of species and, thus, the study of that effect in additional species was essential for reaching a more firm conclusion. Furthermore, although it has been suggested that the effect of nest visiting could also depend on nest predator community, no study has so far tested this hypothesis yet. Trying to detect possible influence of nest-visiting rates and predator community on nesting success we visited European blackbird Turdus merula nests at two different experimental rates in two populations that considerably differ in the composition of their nest predator communities and natural nest predation rates. Contrary to the traditional ideas, our results not only show that investigator disturbance significantly reduces nest predation, but also that this reduction is maintained in both populations despite the difference in the community of nest predators. We discuss these findings and suggest that predators, especially mammals, might avoid places disturbed by investigators. [source]

The influence of parental behavior on vulnerability to nest predation in tropical thrushes of an Andean cloud forest

JOURNAL OF AVIAN BIOLOGY, Issue 6 2009
Konrad Halupka
The Skutch hypothesis predicts that parental activity around the nest may attract the attention of predators and thus, in the tropics where predation pressure may be high, selection favors reduced parental activity. This hypothesis has been questioned by studies demonstrating that parents can decrease the risk of nest predation through nest defense. The link between parental activity and predation risk may be further confounded by nest site characteristics. We examined the effects of parental behavior and nest site on clutch survival in two sympatric tropical thrushes (Myadestes ralloides and Turdus leucops). We compared survival rates of clutches in three treatments: 1) natural nests at the incubation stage, 2) unattended nests (un-manipulated nests of the same species, with clutches unattended by parents), and 3) exposed clutches (eggs exposed in unconcealed positions, unprotected by the nest). Parental activity had a positive effect on clutch survival, which was revealed by significantly higher survival rate of clutches in attended nests compared to unattended nests. The effect of nest site was less clear: clutches in unattended natural nests survived better than clutches in exposed sites selected by humans, but results were insignificant. We propose that parent birds can exclude a group of opportunistic predators, that are able to destroy unattended clutches. Nest site characteristics may be less important in determining clutch survival in the tropics, where predator guilds are more diverse, making completely safe sites difficult to find. Our results challenge Skutch's hypothesis and point to the need for more data from tropical latitudes. [source]

Putting density dependence in perspective: nest density, nesting phenology, and biome, all matter to survival of simulated mallard Anas platyrhynchos nests

JOURNAL OF AVIAN BIOLOGY, Issue 3 2009
Johan Elmberg
Breeding success in ground-nesting birds is primarily determined by nest survival, which may be density-dependent, but the generality of this pattern remains untested. In a replicated crossover experiment conducted on 30 wetlands, survival of simulated mallard nests was related to "biome" (n=14 mediterranean and 16 boreal wetlands), breeding "phenology" (early vs late nests), and "density" (2 vs 8 nests per 225 m shoreline). Local abundances of "waterfowl", "other waterbirds", and "avian predators" were used as covariates. We used an information-theoretic approach and Program MARK to select among competing models. Nest survival was lower in late nests compared with early ones, and it was lower in the mediterranean than in the boreal study region. High-density treatment nests suffered higher depredation rates than low-density nests during days 1,4 of each experimental period. Nest survival was negatively associated with local abundance of "waterfowl" in the boreal but not in the mediterranean biome. Effect estimates from the highest-ranked model showed that nest "density" (d 1,4) had the strongest impact on model fit; i.e. three times that of "biome" and 1.5 times that of "phenology". The latter,s effect, in turn, was twice that of "biome". We argue that our study supports the idea that density-dependent nest predation may be temporally and spatially widespread in waterfowl. We also see an urgent need for research of how waterfowl nesting phenology is matched to that of prey and vegetation. [source]

Evolution of avian clutch size along latitudinal gradients: do seasonality, nest predation or breeding season length matter?

JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 5 2010
E. M. GRIEBELER
Abstract Birds display a latitudinal gradient in clutch size with smaller clutches in the tropics and larger in the temperate region. Three factors have been proposed to affect this pattern: seasonality of resources (SR), nest predation and length of the breeding season (LBS). Here, we test the importance of these factors by modelling clutch size evolution within bird populations under different environmental settings. We use an individual-based ecogenetic simulation model that combines principles from population ecology and life history theory. Results suggest that increasing SR from the tropics to the poles by itself or in combination with a decreasing predation rate and LBS can generate the latitudinal gradient in clutch size. Annual fecundity increases and annual adult survival rate decreases from the tropics to the poles. We further show that the annual number of breeding attempts that (together with clutch size) determines total annual egg production is an important trait to understand latitudinal patterns in these life history characteristics. Field experiments that manipulate environmental factors have to record effects not only on clutch size, but also on annual number of breeding attempts. We use our model to predict the outcome of such experiments under different environmental settings. [source]

Breeding biology of White-rumped Tanagers in central Brazil

JOURNAL OF FIELD ORNITHOLOGY, Issue 3 2010
Luane R. Dos Santos
ABSTRACT White-rumped Tanagers (Cypsnagra hirundinacea) are widely distributed in northern Brazil, Bolivia, and Paraguay, and are classified as vulnerable in the state of Paraná and as endangered in the state of São Paulo, Brazil. Little is currently known about their breeding biology. We studied the breeding behavior of White-rumped Tanagers in the Cerrado (Neotropical savanna) in central Brazil from 2002 to 2007. The breeding period extended from mid-August to mid-December. Nests were cup-shaped and located mainly in trees of the genus Kielmeyera at a mean height of 3.7 ± 0.3 m (SE). Clutch sizes varied from one to three eggs and the incubation period lasted an average of 16.0 ± 0.3 d. Incubation was by females only and started with the laying of the first egg. Mean nest attentiveness (percent time on nests by females) was 64 ± 0.08%. Nestlings were fed by males, females, and, when present, helpers. The mean rate of food delivery rate to nests was 5.2 ± 0.4 items/h, with rates similar for males (mean = 2.7 ± 0.3 items/h) and females (mean = 2.4 ± 0.3 items/h). The mean duration of the nestling period was 12.1 ± 0.5 d. Compared to many temperate species of tanagers, White-rumped Tanagers in our study had relatively small clutches, low nest attentiveness, and long incubation periods. As with other tropical species, such characteristics might be due to food limitation or high rates of nest predation. RESUMEN Cypsnagra hirundinacea está ampliamente distribuida desde el norte de Brasil, Bolivia y Paraguay, y está clasificada como vulnerable en el estado de Paraná y en peligro en el estado de São Paulo, Brasil. Actualmente poco es conocido sobre su biología reproductiva. Estudiamos el comportamiento reproductivo de C. hirundinacea en el cerrado (Sabana Neotropical) en la región central de Brasil desde el 2002 hasta el 2007. El periodo reproductivo se extiende desde mediados de agosto hasta mediados de diciembre. Los nidos en forma de copa estaban localizados principalmente en arboles del genero Kielmeyera a una altura promedio de 3.7 ± 0.3 (ES) m. El tamaño de la nidada vario entre uno y tres huevos y el periodo de incubación duro en promedio 16 ± 0.3 días. La incubación fue realizada exclusivamente por la hembra y comenzó después de la puesta del primer huevo. El promedio de atención al nido (porcentaje del tiempo en el nido por parte de la hembra) fue de 64 ± 0.08%. Los polluelos fueron alimentados por el macho, la hembra y, cuando estaban presentes, ayudantes. El promedio de la tasa de alimentación al nido fue de 5.2 ± 0.4 viajes/hr, con tasas similares entre el macho (promedio = 2.7 ± 0.3 viajes/hr) y la hembra (promedio = 2.4 ± 0.3 viajes/hr). El promedio de duración del periodo de polluelos fue de 12.1 ± 0.5 días. Comparado con muchas especies de tangaras de la zona temperada, C. hirundinacea tiene una nidada relativamente pequeña, baja atención al nido y un periodo largo de incubación. Pero las diferencias con otras especies tropicales en estas variables se pueden deber a variación en la disponibilidad de alimento o altas tasa de depredación. [source]

Effects of nest-site characteristics and parental activity on cowbird parasitism and nest predation in Brown-and-yellow Marshbirds

JOURNAL OF FIELD ORNITHOLOGY, Issue 1 2009
Walter S. Svagelj
ABSTRACT Nest-site selection and nest defense are strategies for reducing the costs of brood parasitism and nest predation, two selective forces that can influence avian nesting success and fitness. During 2001,2002, we analyzed the effect of nest-site characteristics, nesting pattern, and parental activity on nest predation and brood parasitism by cowbirds (Molothrus spp.) in a population of Brown-and-yellow Marshbirds (Pseudoleistes virescens) in the Buenos Aires province, Argentina. We examined the possible effects of nest detectability, nest accessibility, and nest defense on rates of parasitism and nest predation. We also compared rates of parasitism and nest predation and nest survival time of marshbird nests during the egg stage (active nests) with those of the same nests artificially baited with passerine eggs after young fledged or nests failed (experimental nests). Most nests (45 of 48, or 94%) found during the building or laying stages were parasitized, and 79% suffered at least one egg-predation event. Cowbirds were responsible for most egg predation, with 82 of 107 (77%) egg-predation events corresponding to eggs punctured by cowbirds. Nests built in thistles had higher rates of parasitism and egg predation than nests in other plant, probably because cowbirds were most active in the area where thistles were almost the only available nesting substrate. Parasitism rates also tended to increase as the distance to conspecific nests increased, possibly due to cooperative mobbing and parental defense by marshbirds. The proportion of nests discovered by cowbirds was higher for active (95%) than for experimental (29%) nests, suggesting that cowbirds used host parental activity to locate nests. Despite active nest defense, parental activity did not affect either predation rates or nest-survival time. Thus, although nest defense by Brown-and-yellow Marshbirds appears to be based on cooperative group defense, such behavior did not reduce the impact of brood parasites and predators. RESUMEN La selección del sitio de nidificación y defensa del nido son estrategias que reducen los costos del parasitismo de cría y predación de nidos, dos fuerzas selectivas que pueden afectar el éxito reproductivo y la eficacia biológica de las aves. Durante 2001,2002, analizamos el efecto de las características del sitio de nidificación, patrón de nidificación, y actividad parental en la predación de nidos y parasitismo de cría por tordos (Molothrus spp.) en una población de Pseudoleistes virescens en la provincia de Buenos Aires, Argentina. Examinamos los posibles efectos de la detectabilidad, accesibilidad y defensa del nido en las tasas de parasitismo y depredación de nidos. Asimismo, se compararon las tasas de parasitismo, depredación, y tiempo de supervivencia de los nidos entre los estadios de huevo (nidos activos) con los de los mismos nidos cebados artificialmente con huevos de passerinos (nidos experimentales). La mayoría de los nidos (45 de 48, o 94%) hallados durante los estadios de construcción y puesta fueron parasitados, donde el 79% de los nidos sufrieron al menos un evento de predación de huevos. Los tordos fueron responsables de la mayoría de los eventos de predación de huevos, donde 82 de 107 (77%) eventos de predación correspondieron a huevos picados por tordos. Los nidos construidos en cardos tuvieron tasas de predación y parasitismo más altas que las correspondientes a nidos construidos en otros sustratos, probablemente debido a que los tordos exhiben una mayor actividad en el área donde los cardos son el único sustrato de nidificación disponible. La tasa de parasitismo mostró una tendencia a crecer con la distancia al nido más próximo, probablemente debido a la defensa parental y los despliegues de defensa comunales de Pseudoleistes virescens. La proporción de nidos descubiertos por tordos fue mayor para nidos activos (95%) que para nidos experimentales (29%), lo cual sugiere que los tordos utilizaron la actividad parental para detectar los nidos. A pesar de la activa defensa del nido, descubrimos que la actividad parental no afectó ni la tasa de predación ni el tiempo de supervivencia de los nidos. De esta forma, a pesar de que la defensa del nido en Pseudoleistes virescens aparenta estar basada en la defensa cooperativa grupal, tal comportamiento no redujo el impacto de los parásitos de cría o predadores de nidos. [source]

Nest-site selection by Common Black-Hawks in southwestern New Mexico

JOURNAL OF FIELD ORNITHOLOGY, Issue 1 2008
Giancarlo Sadoti
ABSTRACT Despite the interest of resource managers and conservationists in the status of Common Black-Hawk (Buteogallus anthracinus) populations in the southwestern United States, little is known about their nesting success and habitat requirements. Because such information is essential for effective population and habitat management, I examined the nesting success and nest-site selection of Common Black-Hawks in southwestern New Mexico during 2000 and 2001. Of the 37 nesting attempts in 21 territories, ,1 young fledged from 25 nests (68%). Comparison of nest-sites and nonused sites suggested that breeding Common Black-Hawks selected nest-sites in areas with a sparser and shorter subcanopy tree layer and in trees with a smaller trunk diameter and a greater minimum crown diameter. These differences appear to be related to variation in forest ages within territories, with nonused sites having fewer, but older, canopy trees than nest-sites. Sites with younger, smaller subcanopy trees may provide forest structure for more effective foraging, whereas the characteristics of younger nest tree canopies may reduce the risk of nest predation or offer more protection from inclement weather. Due to the limited range of this species in the southwestern United States, efforts to encourage the establishment and maturation of riparian forests in Common Black-Hawk breeding areas could be important in sustaining available nesting habitat and, in turn, maintaining or expanding current population levels. SINOPSIS Aunque existe interés de parte de profesionales en manejo de recursos y conservacionistas en el estatus de las poblaciones de Buteogallus anthracinus en el sudoeste de los Estados Unidos, poco se conoce sobre su éxito de anidamiento y requerimientos de hábitat. Por la razón que esta información es esencial para el éxito del manejo poblacional y del hábitat para esta especie, examiné el éxito de anidamiento y la selección del lugar de anidamiento de Buteogallus anthracinus en el sudeste del estado de Nueva México durante el 2000 y el 2001. De los 37 intentos de anidamiento en 21 territorios, ,1 de los polluelos volaron de 25 nidos (68%). Una comparación entre lugares donde se ubicaban los nidos y sitios no utilizados para anidar indica que individuos seleccionaron lugares para anidar en áreas con una menor cobertura y una menor altura del sub-dosel. Adicionalmente, los nidos fueron ubicados en árboles con un menor diámetro del tronco y con un mayor diámetro mínimo de la corona. Estas diferencias parecen ser relacionadas a la variación en la edad del bosque dentro de los territorios, con sitios no utilizados caracterizados por un número menor de árboles del dosel pero las cuales tienen una edad mayor que los árboles del dosel en los sitios donde se ubicaron los nidos. Sitios con árboles en el sub-dosel de menor edad y de menor tamaño podrían proveer la estructura del bosque necesaria para un forrajeo mas efectivo, mientras que las características de las coronas de los árboles de menor edad en la cual se encuentra el nido podrían reducir el riesgo de la depredación del nido o proveer mas protección de mal tiempo. Dado el rango limitado de esta especie en el sudeste de los Estados Unidos, los esfuerzos para animar el establecimiento y la maduración de los bosques riparios en las áreas de anidamiento de esta especie podrían ser importantes para mantener el hábitat disponible para anidar y a la vez mantener o expandir los tamaños actuales de las poblaciones. [source]

Breeding biology of Eared Quetzals in the Sierra Madre Occidental, Mexico

JOURNAL OF FIELD ORNITHOLOGY, Issue 1 2008
José I. González-Rojas
ABSTRACT Eared Quetzals (Euptilotis neoxenus), a threatened species, are one of the least studied trogons in Mexico. We monitored 29 Eared Quetzal nests in the Chihuahuan portion of the Sierra Madre Occidental from 1998 to 2003. All nests were in tree cavities, and the mean tree and nest cavity heights (N= 14) were 16.9 ± 7.8 m and 11.4 ± 4.1 m, respectively. The mean clutch size was 2.8 ± 0.9 eggs (N= 28), the incubation period lasted 22 d (N= 1), and nestling periods ranged from 29 to 31 d (N= 5). Both adults incubated eggs and fed nestlings. Of 80 eggs, 70 hatched (87.5%) and 67 of 70 young fledged (95.7%). Twenty-five of 29 nests (86.2%) produced at least one fledgling. One nest was predated, and two failed when nest trees fell. Higher rates of nest predation have been reported for other species of trogons. However, fewer potential predators, such as snakes and mammals, are present in the Sierra Madre than in tropical zones where most trogon species occur. In addition, antipredator behaviors, including nestlings with calls resembling a snake and nests with an unpleasant odor, may contribute to the high nesting success. The main limiting factors for Eared Quetzals in the northern Chihuahua may be competition for cavities with other secondary cavity-nesters, and the failure of nests when snags fall. SINOPSIS Euptilotis neoxenus es un ave amenazada y uno de los trogones menos estudiados de México. Monitoreamos 29 nidos en la Sierra Madre Occidental de Chihuahua durante seis años (1998,2003). Todos los nidos se encontraron en cavidades de árboles, 11 de los 14 nidos caracterizados fueron localizados en álamos (Populus tremuloides). La altura promedio de los árboles y los nidos fue de 16.9 ± 7.8 m y 11.38 ± 4.05 m, respectivamente. El tamaño de puesta fue de 2.8 ± 0.9 huevos (N= 28), el periodo de incubación duró 22 días (N= 1) y el de anidamiento 28,31 días (N= 5). Ambos adultos incubaron y alimentaron a los pollos. De 80 huevos, 70 eclosionaron (87.5%) y 67 fueron volantones (95.7%). Veinticinco de los 29 nidos (86.2%) produjeron al menos un volantón. Un nido fue depredado y dos se perdieron debido a la caída del árbol que los albergaba. Para otras especies de trogones han sido reportadas tasas de depredación más altas. Sin embargo, en la Sierra Madre Occidental existen una menor cantidad de depredadores potenciales, como serpientes y mamíferos, que en las zonas tropicales donde la mayoría de las especies de trogones está presentes. Además, comportamientos anti-depredación, incluyendo polluelos con llamados que asemejan una serpiente y nidos con un olor desagradable, podrían contribuir a un éxito reproductivo alto. Los principales factores limitantes para la productividad de esta especie son la competencia por cavidades con otras especies y la pérdida de nidos cuando los árboles en decadencia caen. [source]

Nesting behavior and breeding success of Hoatzins

JOURNAL OF FIELD ORNITHOLOGY, Issue 4 2007
Antje Müllner
ABSTRACT Hoatzins (Opisthocomus hoazin) are the only member of the family Opisthocomidae and are found only in forests in the Amazon and Orinoco river basin of South America. Although locally common in riparian habitats, information about their natural history is based almost exclusively on observations from gallery forests in the "llanos" (savannahs) of Venezuela. We investigated the nesting activities of Hoatzins in a primary rainforest in Amazonian Ecuador from 1995 to 2000. At our study site, Hoatzins live and breed in the inundated forests that surround lakes and river channels. Egg laying occurred from February to July and from September to November, but always peaked in April, May, and June. The mean clutch size was 2.4 ± 1.1 eggs (N= 291; range = 1,7), but 51% of all clutches contained two eggs. The mean duration of the incubation period was 32 ± 1.5 d (N= 20) and, overall, 17% of Hoatzin nests fledged at least one young. The main cause of nest failure was predation, with birds and snakes being the most frequent predators. Hoatzin reproduction was closely linked to the rainy season, and such timing may be influenced by increased food availability (high water levels cause leaf fall and the subsequent growth of new leaves coincides with the beginning of the feeding period of the young) and reduced risk of nest predation by mammalian predators when water levels are high. Our results indicate that the breeding biology of Hoatzins in tropical rainforest habitat, including small clutch sizes and low annual reproductive success, is similar to that of tropical passerines and provides further support for the existence of typical life history characteristics for tropical birds. SINOPSIS Las hipótesis relacionadas con la variación altitudinal en los ciclos de vida de aves están basadas en una gran cantidad de datos de aves de zona templada, mientras que para el trópico inclusive se desconoce la biología básica. Esto aplica en particular para aves que no son paserinos. Investigamos las actividades de anidamiento de Hoatzin (Opisthocumus hoazin) en un bosque pluvial primario de la amazonia ecuatorial. En nuestra área de estudio, los hoatzines viven y se reproducen en bosques inundados que bordean lagos y canales. Los intentos reproductivos estuvieron asociados a la época de lluvias y se agruparon en unos meses del año. Normalmente, estas aves anidan una vez al año. El reanidamiento solo ocurrio cuando hubo pérdidas durante la época de puesta. Los nidos fueron construidos en los árboles y arbustos más comunes en el hábitat. El número de huevos por camada vario de uno a siete, aunque el 51% de las camadas consistieron de dos huevos. El tiempo promedio de incubación fue de 32 días. El exito promedio de eclosionamiento (para todos los nidos) fue de 34% y el 50% de los pichones dejaron el nido, lo que dio un éxito de anidamiento en general de 17%. La causa principal de pérdida de nidos lo fue la depredación, en donde otras aves y culebras resultaron ser los principales depredadores. La pequeña ventana de tres meses para reproducirse parece ser el resultado de un fuerte constreñimiento para una reproducción exitosa, debido a una mejor protección de los nidos y mayor abundancia de alimentos durante la época de inundación. El hoatzin exhibe un ciclo de vida similar al de paserinos tropicales. Esto indica la efectividad de las presiones ambientales de selección que deben estar envueltas en la formación de dichos trasos. [source]

A portable system for continuous monitoring of bird nests using digital video recorders

JOURNAL OF FIELD ORNITHOLOGY, Issue 3 2007
Andrew J. Pierce
ABSTRACT A variety of photographic methods have been described for monitoring nest predation. All have limitations for studying active nests in remote situations, such as size, expense, volume of data recorded, and types of trigger mechanisms. We developed a digital video surveillance system using infrared cameras to monitor predation at bird nests. The main advantage of this system over other video recorders is the small size of the recorder that can run continuously at 29 frames/s for more than 3 days. The recorder's built-in monitor makes it more transportable and allows for easy setup. Digital data is compact, can be reviewed quickly, and requires less physical storage space than videotapes. We recorded nest predation by mammals, birds, and snakes as well as egg and nestling losses not caused by predation. System failure rates were low and the total cost was comparable to ($700 US) video cassette recorders that are often used to monitor nests. SINOPSIS Se han descrito una gran variedad de métodos fotográficos para monitorear la depredación de nidos. Todos los métodos tienen limitaciones para estudiar nidos activos a distancia, como su tamaño, costo, volumen de los datos grabados y mecanismos para activar el equipo. Desarrollamos un sistema digital de vigilancia, utilizando cámaras infrarrojas para monitorear la depredación de nidos. La ventaja principal de este equipo sobre otros similares es el tamaño de la grabadora, la cual puede funcionar continuamente a 29 cuadros/s por más de tres días. El monitor integrado a la cámara hace que el equipo que sea más fácil de transportar y permite que se pueda montar con facilidad. Los datos digitales son compactos, se pueden revisar rápidamente, y requieren menos espacio de almacenaje que las cintas de video convencionales. Grabamos depredación de nidos por mamíferos, aves y culebras al igual que la pérdida de huevos y pichones por otras causas. La tasa de malfuncionamiento fue baja y el costo del equipo ($700 US) es comparable a otros equipos de videograbación a cassette que se utilizan frecuentemente para monitorear nidos. [source]

Observations of predation by corvids at a Marbled Murrelet nest

JOURNAL OF FIELD ORNITHOLOGY, Issue 2 2007
Percy N. Hébert
ABSTRACT Unlike other alcids, Marbled Murrelets (Brachyramphus marmoratus) typically nest solitarily on large platforms in the upper canopy of old-growth coniferous trees. Although Marbled Murrelets exhibit characteristics that minimize the risk of predation, habitat fragmentation has likely increased the risk of nest predation by corvids. Using a video camera at a nest in northern California, we observed nest fates for 4 yr (2002,2005). These recordings revealed two cases of egg predation by a Steller's Jay (Cyanocitta stelleri) and a Common Raven (Corvus corax), respectively. In both instances, the egg was carried from the nest site, leaving no evidence that nesting had occurred. Our observations revealed (1) the need to be conservative in estimates of nesting attempts and nesting success of Marbled Murrelets based only on the presence or absence of eggshell fragments or feces, (2) that not all predation attempts were successful, and (3) that murrelets may be more susceptible to predation early in the incubation period when adults may be less attentive to eggs and, after hatching, when young are less than 14 d old. We encourage efforts to minimize anthropogenic activities that may increase local corvid densities or disturb murrelets during the early incubation period. SINOPSIS Contrario a otros álcidos, la uria (Brachyramphus marmoratus), anida comunmente, de forma solitaria en grandes plataformas en el docel de bosques maduros de coníferos. Aunque estas aves exhiben características que minimizan el riesgo de depredación, la fragmentación de habitat ha incrementado el mismo, particularmente por parte de córvidos. Utilizando una cámara de video en un nido en el norte de California,observamos el fracaso de nidos por cuatro años (2002,2005). Las grabaciones revelaron dos casos de depredación de huevos por parte de Cyanocitta stelleri y Corvus corax, respectivamente. En ambos casos, los huevos fueron cargados, y no se dejo evidencia de depredación. Nuestras observaciones revelan: (1) la necesidad de ser conservador cuando hace estimados de intentos de anidamiento y éxito de anidamiento de urias basado en la presencia o ausencia de fragmentos de cascarones o heces fecales, (2) que no todos los intentos de depredación fueron exitosos, y (3) que el ave estudiada pudiera ser más suceptibles a la depredación temprano en el periodo de incubación, cuando los adultos pudieran darle menor atención a los huevos, y luego del eclosionamiento, cuando los pichones tienen menos de 14 días. Fomentamos los esfuerzos para minimizar actividades antropogénicas que puedan incrementar las densidades locales de córvidos o el disturbio de urias durante las etapas tempranas de incubación. [source]