Correlation between nectar supply and aggression in territorial honeyeaters: causation or coincidence?
✍ Scribed by Doug P. Armstrong
- Book ID
- 104651555
- Publisher
- Springer
- Year
- 1992
- Tongue
- English
- Weight
- 1022 KB
- Volume
- 30
- Category
- Article
- ISSN
- 0340-5443
No coin nor oath required. For personal study only.
✦ Synopsis
A fundamental prediction of food-based economic models of territoriality is that animals will not defend territories if food is so abundant that defense will not improve access to food. Several studies of nectar-feeding birds support this prediction, with territoriality being rare or absent in years when nectar was particularly abundant. However, these results could potentially be an artefact of changes in bird density with nectar availability, and in at least some cases the correlations between territory defense and nectar availability could be purely coincidental. This paper reports the first experimental test of whether cessation of territory defense in nectar-feeding birds results from a direct response to abundance of nectar. New holland honeyeaters Phyli- donyris novaehollandiae and white-cheeked honeyeaters P. nigra show pronounced changes in their levels of territorial aggression over the 7-8 months that they breed. These changes are predictable from economic considerations in that the birds are least aggressive in the months when nectar is extremely abundant. I tested whether the birds were responding to changes in nectar availability by providing sugar-water feeders at "neutral" locations that were easily accessible to territory holders, but far enough away from territories that intrusion rates were unaffected. I tested for responses at two time scales: feeders were put out for 48-h periods in 1987, and were left out continuously from January to October 1988. The only effect was that territory holders visited feeders instead of flowers when floral nectar was scarce. They continued to defend their territories aggressively at those times, showed seasonal changes in aggressiveness similar to birds on a site without feeders, and did not shift their territories toward feeders. I conclude that the observed changes in aggressiveness are not responses to changes in nectar availability, and suggest alternative explanations.