Recent models of parent-offspring communication suggest that nestling begging reliably reflects food requirements, and therefore should increase with nestling need. Need may be affected by short-term variations in hunger, as well as by long-term factors such as relative size, growth rate and body condition. In the present study, the brood sizes of barn swallows were manipulated to create differ...

Food availability is an important limiting factor for avian reproduction. In altricial birds, food limitation is assumed to be more severe during the nestling stage than during laying or incubation, but this has yet to be adequately tested. Using food-supplementation experiments over a 5-year period, we determined the degree and timing of food limitation for burrowing owls (Athene cunicularia) ...

This study presents data relevant to the hypothesis that the energy expenditure associated with begging influences the signalling of need by nestling birds. We used open-circuit respirometry to measure the energy costs of resting, begging and non-begging activities in nestling house wrens, Troglodytes aedon, ranging in age from 1 to 11 days post-hatching. Across all ages, begging caused a 27% i...

The effect of insect vectors on avian exposure to infection by pathogens remains poorly studied. Here, we used an insect repellent treatment to reduce the number of blood-sucking flying insects in blue tit Cyanistes caeruleus nests and examined its effect on nestling health status measured as body mass, nestling phytohaemagglutinin (PHA) response and blood parasite prevalence. We found that (i)...

We analysed growth of nestling Chilean Swallows (Tachycineta meyeni) over four consecutive breeding seasons and determined the factors that explain variation in growth rate, asymptotic body mass and length of the nestling period. As the breeding season advanced nestlings grew more slowly and attained lower asymptotic mass, but the length of the nestling period and nestling survival did not show...

In birds, the quality of rearing conditions is a major determinant of nestling body condition, nestling survival and recruitment probability (Martin 1987). When food becomes short, sibling competition increases (Mock & Parker 1997), growth is depressed (Smith et al. 1989), and chicks are more vulnerable to environmental stress factors (Hoffmann & Merila 1999). Although the effect of rearing con...

Antarctic fulmarine petrels breed in some of the coldest conditions encountered by any bird and their young grow twice as fast as predicted allometrically. To examine the energetic consequences of fast growth in a cold environment, we used the doubly labeled water technique to measure field metabolic rates of adults (three species) and different-aged nestlings (four species) of Antarctic fulmar...

The effects of acute environmental stressors on reproduction in wildlife are often difficult to measure because of the labour and disturbance involved in collecting accurate reproductive data. Stress hormones represent a promising option for assessing the effects of environmental perturbations on altricial young; however, it is necessary first to establish how stress levels are affected by envi...

Speciation can be seen as the establishment of reproductive barriers among species. Hybrid zones provide us with an ideal situation to study the process of speciation because the evolution of reproductive isolation is still in progress. Hybrids usually suffer reduced fitness (i.e. leading to post-zygotic isolation) although they may have higher or similar fitness as the parental species in some...

Begging by nestling birds has been used to test evolutionary models of signalling but theory has outstripped evidence. Eavesdropping predators potentially impose a cost on begging that ensures signal honesty, yet little experimental evidence exists for such a cost at active nests because the use of artificial nests, long playback bouts and absence of parents may have exaggerated costs. We broad...