Breeding Adults (breeding + adult)

Distribution by Scientific Domains

Selected Abstracts

Postfledging habitat selection of juvenile middle spotted woodpeckers: a multi-scale approach

ECOGRAPHY, Issue 4 2009
Carlos Ciudad
Despite its relevance for the persistence of populations, the ecological mechanisms underlying habitat use decisions of juvenile birds are poorly understood. We examined postfledging habitat selection of radio-tracked juvenile middle spotted woodpeckers Dendrocopos medius at multiple hierarchically-nested spatial scales in NW Spain. At the landscape and home range scales, old oak forest was the most used and selected habitat, young oak forests and pine plantations were avoided, and riverside forests were used as available. At a lower scale, birds selected larger diameter trees for foraging. Home ranges had higher densities of large deciduous trees (mainly oaks Quercus spp., but also poplars Populus spp. and willows Salix spp. >22,cm and >33,cm DBH) selected for foraging by juveniles than non-used areas. These results suggest that foraging conditions may drive, at least partly, habitat use decisions by juvenile birds. We also discuss the potential influence of intraspecific competition, the search for a future breeding territory in the early postfledging period and predation avoidance on habitat use decisions by juvenile birds. Contrary to previous studies on migrant forest birds, postfledging juvenile woodpeckers selected the same habitat as for the breeding adults (i.e. old oak forest), indicating that migrant and resident specialist avian species may require different conservation actions. Conservation strategies of woodpecker populations should consider the protection of old oak forests with high densities of large trees to provide suitable habitat to breeding adults and postfledging juveniles. The habitat improvement for this indicator and umbrella species would also favour other organisms that depend on characteristics of old-growth oak forests. [source]

Reproductive strategies in small populations: using Atlantic salmon as a case study

F. Juanes
Abstract,,, Wild salmonid populations with only a few breeding adults may not exhibit a significant reduction in genetic variability compared with larger populations. Such an observation suggests that effective population sizes are larger than population size estimates based on direct adult counts and/or the mating strategy maximises outbreeding, contributing to increased heterozygosity. In the case of wild Atlantic salmon Salmo salar populations, stratification by age classes and sexes on the spawning grounds avoids inbreeding and increases genetic variability. We studied the breeding composition of four Spanish salmon populations. Over a 7-year period we concluded that the probability of within-cohort mating is very low: females generally reproduce after two sea-winters whereas males reproduce mostly as one sea-winter (grilse) and/or mature parr. Considering different levels of contribution of mature parr to spawning derived from field surveys, we developed a simple model for estimating effective population sizes and found that they doubled with 65% parr contribution expected for rivers at this latitude (43N), and ranged from 100,800 individuals. The effect of between-cohort mating was modelled considering different ranges of differences in allele frequencies between cohorts and resulted in 28,50% increases in heterozygosity when considering a 65% parr contribution. The complex mating strategy of Atlantic salmon contributes to explain the high levels of genetic variability found for small populations of this species. This model can probably be extended to other animal species with mating strategies involving different cohorts. [source]

Are House Wren Troglodytes aedon eggs unusually strong?

IBIS, Issue 2 2002
Test of the predicted effect of intraspecific egg destruction
As a result of opposing selective forces, the external strength of avian eggs should be near some size-specific optimum. However, in certain situations there should be selection on females to lay unusually strong eggs. According to one hypothesis, intraspecific egg destruction should favour increased egg strength as a means of defence against conspecific intruders. This hypothesis predicts that House Wrens Troglodytes aedon, a species well known for its tendency to destroy conspecific clutches, should be under selection for unusually strong eggs. However, the intensity of selection for strong eggs should also be modified by efficacy of nest defence against conspecific intruders in a given species (i.e. efficient nest defence by the breeding pair should weaken selection for unusually strong eggs). The goals of our study were: (1) to establish whether House Wren eggs are stronger than expected for their size; (2) to determine which structural mechanisms are responsible for their unusual strength; and (3) to test a hypothesis that, between wren species, the efficacy of nest defence and the intensity of egg-destroying behaviour affect the intensity of selection for unusually strong eggs. Our results demonstrated that: (1) House Wren eggs are 1.9 times stronger than expected for their size; (2) their unusual strength is achieved mostly by their unusually thick shells; and (3) eggs of the House Wren (extensive paternal nest defence; male egg-destroying behaviour suppressed during incubation) are significantly weaker structurally than eggs of the Marsh Wren Cistothorus palustris (reduced paternal nest defence; male egg-destroying behaviour present throughout incubation). These results are consistent with the hypothesis that the intraspecific egg-destroying behaviour and the efficacy of nest defence by the breeding adults have played a role in the evolution of strength of House Wren eggs. [source]

Survival in a long-lived territorial migrant: effects of life-history traits and ecological conditions in wintering and breeding areas

OIKOS, Issue 4 2009
Juan M. Grande
Despite its key role in population dynamics and evolutionary ecology, little is known about factors shaping survival in long-lived territorial species. Here, we assessed several hypotheses that might explain variability in survival in a migratory Spanish population of a long-lived territorial species, the Egyptian vulture Neophron percnopterus, using a 16-year monitoring period and live-encounter histories of 835 individually marked birds. Cormack-Jolly-Seber capture,recapture models showed no evidence for effects of sex or nestling body condition on survival. However, the normalized difference vegetation index (NDVI; an indicator of primary productivity) of natal territories had positive effects on juvenile survival, indicating that environmental conditions experienced early in life can determine survival prospects. Survival increased with age (0.730.02 in the first 2 years to 0.780.03 in years 3 and 4) to later decrease when birds were five years old (0.600.05), the age at which they acquire the adult plumage, abandon the communal lifestyle of juveniles, and may look for a breeding territory. At older ages, survival was higher for non-breeding (0.750.02) and breeding adults (0.830.02). Among the latter, birds that recruited into better territories had higher survival prospects. Age-specific variation in survival in this species may be related to behavioural changes linked to dispersal and recruitment into the breeding population, while survival prospects of adult birds strongly depend on breeding territory selection. These results suggest a tradeoff between recruiting soon, and thus reducing mortality costs of a long and extensive dispersal period, and trying to recruit into a good quality territory. Finally, annual survival rates for birds of all age classes were positively related with the NDVI in their African wintering grounds. Although this relationship was probably mediated by food availability, further research is needed to properly identify the limiting factors that are affecting trans-Saharan migrants, especially in light of global climate change. [source]