Although several studies have shown that carotenoid-based signals are negatively affected by (metal) pollution, the underlying mechanisms are not well understood. There are two possible, not mutually exclusive, hypotheses to explain the metal-induced fading of carotenoid colouration. Metal pollution could affect oxidative stress levels and/or the diet. We assessed the expression of the yellow b...

Nestling is a defenceless stage in the life of birds in several ways. For instance, the possibilities to escape infection and infestation by several parasitic diseases are greatly reduced in nestlings. This fact implies that a number of strategies and counter strategies could evolve in hosts to avoid parasites and in parasites to locate and exploit young hosts. An increasing number of nestlings...

The effects of age, handling-induced stress, yolk androgens, and body condition on plasma corticosterone levels were investigated in free-living nestling American kestrels, Falco sparverius, a semialtricial falcon species. In an observational study, corticosterone levels varied with age and handling time. Specifically, corticosterone was low until age 15 days and then rose from age 20 through 2...

The offspring of caring parents may evolve specialized traits uniquely adaptive during their dependence on parental care. For example, the mouths of passerine nestlings are often bordered by enlarged and colorful rictal flanges expressed only during the nestling period. Although these traits are commonly hypothesized to act as visual signals during begging, noncommunication functions for the sp...

Evolutionary theory of parent-offspring conflict explains begging displays of nestling birds as selfish attempts to influence parental food allocation. Models predict that this conflict may be resolved by honest signaling of offspring need to parents, or by competition among nestmates, leading to escalated begging scrambles. Although the former type of models has been qualitatively supported by...

BACKGROUND Maternal antibodies are believed to play an integral role in protecting immunologically immature wild-passerines from environmental antigens. This study comprehensively examines the early development of the adaptive immune system in an altricial-developing wild passerine species, the house sparrow (Passer domestics), by characterizing the half-life of maternal antibodies in nestling ...

Comparative hormone studies can reveal how physiology underlies life history variation. Here, we examined seasonal variation in plasma testosterone concentration between populations of male orange-crowned warblers (Vermivora celata) breeding in Fairbanks, Alaska (V. c. celata) and on Santa Catalina Island, California (V. c. sordida). These populations face different ecological constraints and e...

Although individual variation is a key requirement for natural selection, little is known about the magnitude and patterns of individual variation in endocrine systems or the functional significance of that variation. Here we describe (1) the extent and repeatability of inter-individual variation in adrenocortical responses and (2) its relationship to sex-specific phenotypic quality, such as so...

Many Apodidae, including Streptoprocne biscutata (Sclater, 1866), drop eggs from their nests during incubation. This is interpreted as nest site competition or accident. We provide evidence that egg ejection is deliberate and that this behaviour controls the brood size. Brood sizes were manipulated and nestling growth was measured to test the hypothesis that pairs can regulate brood size during...

Carotenoids are an essential and often limiting resource in animals and play important roles in immune system function. In birds, the period shortly after hatching is an energetically demanding stage characterized by rapid growth in body size and organ systems, including the immune system. Availability of carotenoids for the growing nestlings may be of particular importance and potentially limi...