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First Breeding (first + breeding)
Selected AbstractsPulsed resources affect the timing of first breeding and lifetime reproductive success of tawny owlsJOURNAL OF ANIMAL ECOLOGY, Issue 2 2010A. Millon Summary 1.,According to life-history theory, environmental variability and costs of reproduction account for the prevalence of delayed reproduction in many taxa. Empirical estimates of the fitness consequences of different ages at first breeding in a variable environment are few however such that the contributions of environmental and individual variability remains poorly known. 2.,Our objectives were to elucidate processes that underpin variation in delayed reproduction and to assess lifetime consequences of the age of first breeding in a site-faithful predator, the tawny owl Strix aluco L. subjected to fluctuating selection linked to cyclical variation in vole density (typically 3-year cycles with low, increasing and decreasing vole densities in successive years). 3.,A multistate capture,recapture model revealed that owl cohorts had strikingly different juvenile survival prospects, with estimates ranging from 0·08 to 0·33 respectively for birds born in Decrease and Increase phases of the vole cycle. This resulted in a highly skewed population structure with >75% of local recruits being reared during Increase years. In contrast, adult survival remained constant throughout a vole cycle. The probability of commencing reproduction was lower at age 1 than at older ages, and especially so for females. From age 2 onwards, pre-breeders had high probabilities of entering the breeding population. 4.,Variation in lifetime reproductive success was driven by the phase of the vole cycle in which female owls started their breeding career (26,47% of variance explained, whether based on the number of local recruits or fledglings), more than by age at first breeding or by conditions experienced at birth. Females who postponed reproduction to breed for the first time at age 3 during an Increase phase, produced more recruits, even when accounting for birds that may have died before reproduction. No such effects were detected for males. 5.,Sex-specific costs of early reproduction may have accounted for females being more prone to delay reproduction. Contrary to expectations from a best-of-a-bad job strategy, early-hatched, hence potentially higher-quality females were more likely to breed at age 1, but then experienced rapidly declining food resources and so seemed caught in a life-history trap set by the multiannual vole cycle. [source] Parent age differentially influences offspring size over the course of development in Laysan albatrossJOURNAL OF ZOOLOGY, Issue 1 2008D. C. Dearborn Abstract Offspring growth and survival are predicted to be higher for older parents, due to a variety of mechanisms, such as increased breeding experience or greater investment favored by low residual reproductive value. Yet the extent to which parent age affects offspring viability is likely to vary between different aspects of growth and survival, perhaps being most pronounced at the most stressful stages of reproduction. We studied the link between parent age and nestling growth and survival in the Laysan albatross, a long-lived seabird with a mean first breeding age of 8 years. Offspring of older parents were more likely to survive to fledging. Among those that did fledge, nestlings of older parents grew more rapidly. However, parent age did not influence the eventual asymptotic size that nestlings reached before fledging: fast-growing nestlings of older parents reached 90% of asymptotic size roughly 1 week sooner, but slow-growing nestlings of younger parents eventually caught up in size before fledging. Older parents bred c. 2 days earlier than younger parents, but hatch date did not explain observed variation in offspring success. The extent to which parent age accounted for variation in size of individual nestlings was not constant but peaked near the midpoint of development. This could reflect a time period when demands on parents reveal age-based differences in parental quality. Overall, growth and survival of offspring increased with parent age in this species, even though the late age of first breeding potentially provides a 7-year period for birds to hone their foraging skills or for selection to eliminate low-quality individuals. [source] Experimental Study of Nest-site Selection in the Biscutate Swift (Streptoprocne biscutata, Aves: Apodidae) in Southern BrazilBIOTROPICA, Issue 1 2009Mauro Pichorim ABSTRACT Biscutate swift Streptoprocne biscutata nests are usually built on protected rocky cliff walls. Birds often renest at the same location. Remains of previous nests may offer information about potential nests and quality of nest-sites. Here, we experimentally study nest-site selection to test the hypothesis that information from previous nests is used in current nest-site selection. We placed old nest material at artificial nest-sites to test whether new nest-sites are chosen based on the presence of nesting material. We also tested whether the use of natural nest-sites is influenced by nesting material by creating two types of natural sites: previously used natural nest-sites with vestiges of old nests removed and never used natural nest-sites to which vestiges of old nests were added. In the first experiment, in 139 nest-use opportunities, 16 artificial nest-sites were used, all of which included vestiges. In the second experiment, in 91 nest-use opportunities, four nests were in previously unused but natural locations to which vestiges had been added, 22 nests were in previously used sites without vestiges, and the remaining 65 nests remained unused. Two processes are apparently in action: first, prior experience and memory; second, vestiges indicate where nesting has occurred, possibly useful for first breeding, or for imperfect memory. Previous nesting information may explain why swifts use nesting locations for many years and why new nesting colonies seldom form. This transmission of information suggests that swifts tend to be conservative and nest where previous nesting has occurred. RESUMO Streptoprocne biscutata nidifica em locais protegidos em grandes paredes rochosas, os casais geralmente usam o mesmo local de nidificação ao longo de vários anos. Restos de nidificações prévias podem fornecer informações sobre a qualidade do sítio de nidificação. No presente trabalho, testamos, experimentalmente, a hipótese de que estas aves usam evidências de nidificações prévias para a escolha de um local para a construção do ninho. Para isso, nós instalamos substratos artificiais de nidificação com e sem ninhos de estações reprodutivas anteriores para testar se novos locais de reprodução são escolhidos em função da presença de material nidular. Nós também testamos se o uso de sítios naturais é influenciado pela presença de material nidular por meio de dois tratamentos: sítios naturais previamente usados, mas com todos os vestígios de ninhos velhos removidos e sítios naturais nunca usados adicionados de vestígios de ninhos velhos. No primeiro experimento, de 139 oportunidades de nidificação apenas 16 substratos artificiais foram usados. Entretanto, todos os substratos utilizados possuíam vestígios de nidificações passadas. No segundo experimento, em 91 oportunidades de nidificação quarto ninhos foram construídos em sítios naturais nunca usados aos quais foram adicionados materiais, 22 ninhos foram construídos em sítios previamente usados, mas desprovidos de materiais e os 65 sítios restantes permaneceram sem uso. Com base nos dados obtidos concluímos que, aparentemente, dois processos estão agindo: a experiência anterior e a memória parecem atuar em primeiro lugar, em segundo lugar os vestígios de ninhos funcionam, possivelmente, como um indicativo da qualidade do local para aves que estão nidificando pela primeira vez ou pra os casos de memória imperfeita. Informações sobre nidificações prévias podem explicar porque andorinhões usam os mesmos sítios de reprodução por muitos anos e porque raramente novas colônias reprodutivas são estabelecidas. Esta transmissão de informação sugere que os andorinhões tendem a ser conservativos, nidificando em locais previamente usados para reprodução. [source] | ||||||||||