Keeping it regular: Development of thermoregulation in four tropical seabird species

The thermoregulatory capacity of a species can determine which climatic niche it occupies. Its development in avian chicks is influenced by numerous factors. Furthermore, it is suggested that altricial chicks develop their thermoregulatory capacity post-hatching, while precocial chicks develop aspects of this in the egg. We investigated the development of thermoregulation of four co-occurring seabird species in the Seychelles; namely white, ground-nesting white-tailed tropicbirds (Phaethon lepturus) and tree-nesting fairy terns (Gygis alba); and dark plumaged, tree-nesting lesser noddies (Anous tenuirostris) and ground- and tree-nesting brown noddies (A. stolidus). White-tailed tropicbirds have semi-altricial chicks, while the remaining species have semi-precocial chicks. Cloacal temperatures (Tb) were measured at five day intervals from newly hatched chicks and compared over time, and with adult Tbs. Initial Tbs of all chicks, except fairy terns, were lower than those taken when chicks were older. Brooding cessation generally coincided with feather development, as did an increase in Tb. Mean chick Tb was significantly lower than mean adult Tb for all species, but only white-tailed tropicbird and brown noddy chicks in tree nests differed significantly from mean adult Tb when chick Tb at five day intervals were considered. There was a significant interactive effect of nest site and age on brown noddy chick Tb, but chick colour did not have a significant effect on Tb. However, brown noddy chicks on dune crests maintained a constant Tb sooner than chicks in tree nests. Our results demonstrate that tropical seabird species have a more delayed onset of thermoregulatory capabilities when compared with those in temperate environments, perhaps as nest sites are less thermally challenging. Nest microhabitats and behavioural thermoregulation, are likely more important during early chick development for these species.