Abstract
Foraging decisions tend to drive individuals toward maximising energetic gains within a patchy environment. This study aims to determine the extent to which rainfall, and associated changes in food availability, can explain foraging decisions within a patchy urbanised landscape, using the Australian white ibis as a model species. Ibis density, food consumption rates and food abundance (both natural and anthropogenic) were recorded during dry and wet weather within urban parks in Sydney, Australia. Rainfall influenced ibis density in these urban parks. Of the four parks assessed, the site with the highest level of anthropogenic food and the lowest abundance of natural food (earthworms), irrespective of weather, was observed to have three times the density of ibis. Rainfall significantly increased the rate of earthworm consumption as well as their relative availability in all sites. Overall, these density and consumption measures indicate that anthropogenic derived foods, mainly from direct feeding by people, explain the apparent distribution of ibis across urban parks. However, there was evidence of prey-switching when the availability of natural foods increased following rainfall, perhaps reflecting selection of particular nutrients.
Highlights
Foraging theory suggests that foragers maximise energetic gains by selectively exploiting patches rich in resources and by minimising foraging time in poor patches [1]
The study was conducted in four inner city parks within a 1.5 km2 area in the Sydney central business district (CBD), Australia
Immediately after, rainfall indicates that rainfall may trigger behavioural responses of ibis within the urban environment
Summary
Foraging theory suggests that foragers maximise energetic gains by selectively exploiting patches rich in resources and by minimising foraging time in poor patches [1]. To achieve this, foraging individuals must be able to (1) recognize patch boundaries, (2) estimate patch rewards, and (3) decide when to leave a patch [2]. An individual can modify their behaviour after assessing available resources [3], risks of predation [4], energetic costs associated with foraging [1,5] or by associations with past experience (foraging memory) [6] within the limitations imposed by their capacity to search [7,8]. Urban environments are characterised by broad areas of built structures, impervious surfaces, and fragmented areas of greenspace [15], which are characterised by consistency, with well-watered parks and gardens supporting plant growth and foraging opportunities [16]. Foraging by urban birds is influenced by the presence and size of remnant
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