The thermoregulatory benefits of the communal nest of sociable weavers Philetairus socius are spatially structured within nests

Abstract

Structures built by animals, such as nests, mounds and burrows, are often the product of cooperative investment by more than one individual. Such structures may be viewed as a public good, since all individuals that occupy them share the benefits they provide. However, access to the benefits generated by the structure may vary among individuals and is likely to be an important determinant of social organisation. Here we use the massive, communal nests of sociable weavers Philetairus socius, to investigate whether their thermoregulatory function varies in relation to the size of communal nests, and the position of individual nest chambers within the communal structure. We then examine whether this spatial variation in thermoregulatory function predicts the social organisation of colonies. First, we show that the sociable weavers' communal nests buffer variation in ambient temperature, and reduce temperature variability within nest chambers. The extent of this buffering effect depends significantly on the position of nest chambers within the communal structure, and on the depth to which chambers are embedded within the nest mass. We detected no effect of nest volume on thermoregulatory benefits, suggesting that there are likely to be additional, non-thermoregulatory benefits leading to communal nests. Finally, our results indicate that there may be competition for access to the benefits of the public good, since older birds occupied the chambers with the highest thermoregulatory benefits, where breeding activity was also more common. We discuss how the spatial structure of the benefits of the public good might influence social organisation in the unique communal lifestyle of sociable weavers.

At home with the birds:Kalahari tree skinks associate with sociable weaver nests despiteAfrican pygmy falcon presence

“…A further benefit to skinks using sociable weaver nests is the thermal advantage these sites provide (van Dijk et al 2013). Surprisingly, we found no effect of ambient temperature on skink abundance, which is usually correlated with lizard activity (Cooper and Whiting 2000a).…”

“…1). While colony size is variable, over 300 individual birds can reside in a single nest, in which individual nest chambers are embedded (van Dijk et al 2013). These nests effectively buffer external environmental temperatures (Bartholomew et al 1976;Broadley 2000) and reduce temperature variability within individual nest chambers (van Dijk et al 2013).…”

Relatedness predicts multiple measures of investment in cooperative nest construction in sociable weavers

“…obs.) and individuals gain thermal benefits (van Dijk et al 2013; Leighton and Echeverri 2014), the nest is a public good that is susceptible to exploitation. As predicted by Johnstone and Cant (2008), and previously documented by Leighton (2014b) and van Dijk et al (2013), we find a male bias in nest construction (Fig.…”

“…The nest is composed of a superstructure that houses multiple, disparate chambers where groups of individuals roost at night and use them for breeding during the breeding season (Maclean 1973). Individuals obtain thermal benefits from the communal nest by roosting in the nest chambers (van Dijk et al 2013; Leighton and Echeverri 2014). The thermal benefits are provided to individuals simply by being in the group therefore qualifying the communal nest as a public good (Frank 2010).…”

The design and function of birds' nests

“…However, the thermal benefits of individual nests vary in relation to the size of the communal nest and the position of individual nest chambers within it. This has important consequences for the fitness of individuals as higher quality individuals occupy those nests that maintain heat with the most efficiency (Van Dijk et al 2013). Therefore, while a comparative study indicates that structural materials provide structural support for the parents and offspring (Heenan and Seymour 2011), empirical studies also show that structural materials provide thermoregulatory benefits for the parents and offspring (Kern 1984; Bollazzi and Roces 2010).…”