Brood size and its importance for nestling growth in the Biscutate Swift (Streptoprocne biscutata, Aves: Apodidae)

M Pichorim,Ela Monteiro-Filho

doi:10.1590/s1519-69842008000400022

M Pichorim, Ela Monteiro-Filho

Open Access

https://doi.org/10.1590/s1519-69842008000400022

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Abstract

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 incubation based on current ability to rear nestlings. Natural (control) broods with one, two and three nestlings, and manipulated (experimental) broods reduced to one and increased to two and three young were monitored. Growth rates were measured based on weight, and wing, tail and tarsus lengths of natural and manipulated broods. We compared the slopes of each measure's regression lines of the nestlings of each brood size by t-test. Nestling growth of control nests was similar and relatively little associated with brood size. In broods reduced to one nestling, weight, wing and tail had greater growth rates, and in broods increased to three nestlings growth rates were lower. Weight was most, and tarsus length least influenced by brood size. In general, nestling growth of manipulated nests was inversely proportional to brood size. The results suggest that pairs with larger clutches are in better physical conditions than others. Thus, in experimental broods, pairs are over or under-loaded because feeding activities increase or decrease and these changes affect the growth rate of the nestlings. The present study suggests that egg ejection can control brood size. This behaviour is probably stimulated by physical changes in the adult birds during incubation.

Highlights

Apodidae are generally classified as altricial or nidicolous with regard to their post-embryonic development (Chantler and Driessens, 1995)
Rates of weight gain and growth of wing, tail and tarsus were similar in the control nests
The brood size did not influence the development of nestlings in these nests

Summary

Introduction

Apodidae are generally classified as altricial or nidicolous with regard to their post-embryonic development (Chantler and Driessens, 1995). That at least in Streptoprocne sporadically larger clutches occur than usual, reaching up to four eggs, two is commonest (Pichorim, 1998; Vasconcelos and Ferreira, 2001; Pichorim, 2002) These brood-sizes can be related to environmental variables and, to physical conditions of some females. It has been contemplated that this behaviour, in principle, could be related to environmentally based changes of physical conditions taking place from egg-laying until the end of incubation (Pichorim, 2003) According to this hypothesis, females in good physical condition in the period before egg-laying would lay more eggs, but couples that go through some kind of difficulty during the incubation would tend to exclude part of the brood, reducing the number of young to be reared (Pichorim, 2003). This paper aims to investigate if brood size is related to the parents’ capacity to feed the brood

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