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Scramble competition models of begging predict that junior nestlings will be more affected by food limitation than seniors. These models assume that food allocation is under offspring control and, hence, predict that this change in food distribution is caused by a differential behavioral response by seniors and juniors. By using the bluethroat (Luscinia svecica svecica) as our model species, we induced food limitation by removing the male parent temporarily. We found that, as predicted, food distribution became more biased in disfavor of juniors when food was limited. However, there was no significant difference in the behavioral responses of seniors and juniors (i.e., positioning in the nest or begging postures) to food limitation that could explain the change in food distribution. Hence, there was no evidence that seniors controlled food distribution. As predicted if parents preferentially fed seniors, nestling rank affected food distribution when controlling for variation in nestling behaviors. Furthermore, as expected if the increased skew in food distribution under food limitation was caused by active food allocation by parents, nestling rank had a greater effect on food distribution under food limitation than under normal conditions. The present study suggests that food distribution in passerine birds is determined not only by nestling behaviors (begging posture and positioning) alone but also by parental preferences for seniors based on nonsignaling cues, such as body size. [ABSTRACT FROM AUTHOR]

Although it is now well established that the conspicuous male plumage colors of many birds have been subject to sexual selection by female choice, it is still debated whether females mate with colorful males to obtain direct or indirect benefits. In species where males provide substantial parental care, females may obtain direct benefits from mating with the males that are best at providing care. The good parent hypothesis suggests that male plumage coloration signals a male's ability to provide parental care. Alternatively, the differential-allocation hypothesis suggests that colorful males reduce their care in response to increased investment by females mated to attractive males. We tested these hypotheses on the bluethroat (Luscinia s. svecica), a socially monogamous, sexually dichromatic bird, in which males have a colorful throat patch consisting of a structurally derived blue area surrounding a melanin-based chestnut spot. Male plumage coloration was objectively quantified by use of reflectance spectrometry. We found no evidence of a relationship between male coloration of either the blue patch or the chestnut spot and the level of paternal care. Nor were there any correlations between male coloration and body size or body condition. Thus, our study does not support the hypothesis that male coloration signals male parental quality (the good parent hypothesis) or the hypothesis that colorful males reduce their care in response to increased investment by females (the differential-allocation hypothesis). [ABSTRACT FROM AUTHOR]