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In altricial birds, the great effort involved in supplying food to nestlings can create trade‐offs in the allocation of resources between the current brood and parental self‐maintenance. In poor foraging conditions, parents have to adjust their energy expenditure in relation to the increased foraging costs. However, intra‐specific variation in parental energy expenditure has rarely been evaluated...
Most bird species exhibit biparental care, but the type of care provided by each sex may differ substantially. In particular, during the incubation phase in passerines, females perform most or all of the incubation, while the male cares for the brood indirectly by feeding the female. However, detailed descriptions of this male investment during the incubation period are missing. Here, we quantitatively...
Avian incubation investment represents a trade‐off between the energetic demands of the parent and the thermal needs of the embryo. Parental energy balance and investment in somatic maintenance relative to incubation investment can be indexed by the rate of feather growth. Feather growth rates, or ptilochronology, of adult Leach's Storm‐Petrels Oceanodroma leucorhoa were used to assess parental investment...
Life‐history theory predicts that hosts may adjust the costs of parasites by altering their reproductive effort. Haemosporidian parasites can affect the reproductive output of wild birds in multiple ways. Thorn‐tailed Rayaditos Aphrastura spinicauda breeding in Navarino Island, southern Chile (55°–40°S), experience a high prevalence of the haemosporidian Leucocytozoon spp., which opens the possibility...
Mothers may produce more of one sex to maximize their fitness if there are differences in the cost of producing each sex or there are differences in their relative reproductive value. Breeding date and clutch size are known to influence offspring sex ratios in birds through sex differences in dispersal, social behaviours, differential mortality and available food resources. We tested whether breeding...
Several bird species construct multiple nests within a single breeding season that are not used for egg‐laying. This behaviour has puzzled researchers for over 100 years, as nests are costly in time and energy to build, and there is no apparent adaptive function. We review the empirical evidence for several suggested non‐exclusive functions and examine the plausibility of each. These functions are:...
Population‐level estimates of offspring sex ratios in birds typically approximate parity whereas biased ratios within nests are not uncommon. In sexually dimorphic raptors, the costs and relative fitness benefits of rearing male and female progeny vary with changing environmental circumstances. This may lead to substantial deviations from balanced investment in offspring of a particular sex by individual...
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