The Effect of Male Incubation Feeding, Food and Temperature on the Incubation Behaviour of New Zealand Robins

Organisms have finite resources, and therefore must make decisions on how to allocate these limited resources between self-care and reproduction. Studying resource allocation trade-offs and reproductive cost is prominent in avian systems because these activities are not mutually exclusive in species which exhibit contact incubation. In the Passeriformes, where over 60% of families exhibit female-only incubation (Deeming 2002), the female faces a trade-off between time allocated to foraging for maintaining her own energy requirements, and the thermal needs of her developing embryos. Females divide the day into periods of foraging (off-bouts), when the unattended clutch begins to equilibrate with the ambient temperature, and incubation periods (on-bouts), when females use energy re-warming their eggs after feeding bouts. This incubation rhythm affects egg temperature and overall nest attentiveness, defined as the proportion of daylight hours spent on the nest. Avian eggs, to hatch successfully, must maintain temperatures that facilitate embryonic development (between 34 and 38 C, Webb 1987; Williams 1996). Therefore, by understanding what factors influence incubation rhythm, we may better explain the enormous variation documented in avian incubation strategies (Conway & Martin 2000a), and how Correspondence Rebecca L. Boulton, Centre for Ornithology, School of Biosciences, Birmingham University, Edgbaston, B15 2TT, UK. E-mail: [email protected]