Present address: Biosis Research Pty Ltd, PO Box 489, Port Melbourne, Victoria 3207, Australia.
Diurnal foraging-mode shifts and food availability in nectarivore assemblages during winter
Article first published online: 26 MAY 2004
Volume 29, Issue 3, pages 264–277, June 2004
How to Cite
TIMEWELL, C. A. R. and MAC NALLY, R. (2004), Diurnal foraging-mode shifts and food availability in nectarivore assemblages during winter. Austral Ecology, 29: 264–277. doi: 10.1111/j.1442-9993.2004.01344.x
- Issue published online: 26 MAY 2004
- Article first published online: 26 MAY 2004
- Accepted for publication August 2003.
- Box-ironbark forests;
- Eucalyptus tricarpa;
Abstract Temporal fluctuations of food resources and foraging activities have been studied extensively, especially at longer timescales (monthly, seasonally, among years). However, short-term variation (e.g. within days) is less well understood. Here we systematically quantified diurnal patterns of foraging by nectarivorous birds (meliphagid honeyeaters) that numerically dominated stands of a winter-flowering eucalypt, the red ironbark, Eucalyptus tricarpa, in central Victoria, Australia. Diurnal variation in food resources also was measured. Data were collected in winter. Anecdotal observations that honeyeaters change from almost exclusive nectarivory early in the day to a higher fraction of insectivory – especially aerial hawking – later in the day were confirmed, although in areas of high flowering intensity, nectar-feeding remained the dominant foraging activity throughout the day. Local climatic factors (ambient temperature, windiness and cloud cover) all varied systematically through the day. Together, results were consistent with a change in foraging emphasis to greater insectivory as a function of elevated activities of insects (especially aerial ones), which was probably fostered by higher ambient temperatures. Contrary to energetic expectations, the nectarivores were very active early in the morning when ambient temperatures averaged approximately 3°C, well below thermoneutral temperatures. We deduced that the potential benefits of gathering as much energy-rich nectar as possible before it was depleted outweighed the high costs of activities at low temperatures.