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

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.Keywords: nestling growth, brood manipulation, brood reduction, incubation.Tamanho da ninhada e sua importância no crescimento de filhotes de Streptoprocne biscutata (Aves: Apodidae) ResumoMuitos Apodidae, incluindo Streptoprocne biscutata (Sclater, 1866), derrubam ovos do ninho durante a incubação. Este comportamento tem sido interpretado como competição ou acidente. Este estudo apresenta evidências de que a expulsão de ovos é deliberada e que esse comportamento controla o tamanho da ninhada. Ninhos com diferentes tamanhos de prole foram manipulados para testar a hipótese de que os casais podem regular o tamanho da ninhada durante a incubação com base em suas capacidades de alimentar os filhotes. Ninhadas naturais (controle) com um, dois e três filhotes e ninhadas manipuladas (experimentais) reduzidas para um e aumentadas para dois e três filhotes foram monitoradas. Foram medidas as taxas de crescimento de massa, asa, cauda e tarso de proles naturais e manipuladas. As inclinações das retas de regressão do desenvolvimento de cada medida ao longo da idade dos filhotes de cada tamanho de ninhada foram comparadas pelo t-teste. O crescimento dos filhotes de ninhos controle foi semelhante e esteve relativamente pouco associado ao tamanho da ninhada. Nas ninhadas reduzidas para um filhote, a massa, asa e cauda apresentaram as maiores taxas de crescimento e nas ninhadas a...

The influence of clutch and brood sizes on nesting success of the biscutate swift, Streptoprocne biscutata (Aves: Apodidae)

“…Following this hypothesis, for the birds food availability is sufficient during good weather to maintain good physical condition, and consequently, they can feed larger broods. Nestling growth of S. biscutata in manipulated nests is inversely proportional to brood size, suggesting that egg ejection is a mechanism for controlling brood size in that species (PICHORIM & MONTEIRO-FILHO 2008). It should be noted that the nests with clutch and brood sizes of two achieved the highest survival rates.…”

Sources of Variation in Enterococci andEnterobacteriaceaeLoads in Nestlings of a Hole-Nesting Passerine

“…Late-breeding pairs tend to offer less or poorer quality food to their nestlings (Naef-Daenzer et al 2000, Rossmanith et al 2007, Wilkin et al 2009. Nestlings in larger broods may also suffer nutritionally from stronger competition with brood mates (Naguib et al 2004, Pichorim & Monteiro 2008. Thus, breeding phenology and brood size could affect the growth of bacteria in digestive tracts through nestling nutrition in terms of quantity and quality.…”