Foraging ecology of urban Galahs: the roles of preadaptation and interspecific competition
||Alan Lill and Elizabeth Polley
There has been a considerable focus on behavioural flexibility and innovative exploitation of novel anthropogenic food resources in avian synurbanization, but the possible influence of preadaptation has received less attention. Interspecific interference competition may be a significant influence on synurbanization, but its influence has also not been very widely examined. Accordingly, we studied Galahs Eolophus roseicapilla
in urban Melbourne in the non-breeding season to determine: (a) if their foraging ecology differed from that reported for nonurban conspecifics, (b) the extent to which they exploited supplementary foods and exhibited innovative foraging on novel foods, and (c) whether they engaged in direct interspecific competition for food with other bird species and the outcome of any such competition. Urban Galahs’ diet was dominated by seeds and roots of exotic grasses (90%); nonurban conspecifics also consume this resource, but many also extensively exploit the seeds of planted cereals and native forage grasses. Urban Galahs exhibited no innovative feeding behaviour and consumed little supplementary anthropogenic food; in contrast, nonurban conspecifics in croplands commonly consume grain provided for livestock or accidentally spilled. Galahs’ foraging behaviour in both environments was dominated by grass-based gleaning and probing, but urban individuals foraged in smaller flocks and did not ‘fell’ tall, non-woody food plants or perch on them above ground level to access seed-heads. Heterospecific birds fed near foraging urban Galahs 50% of the time; however, agonistic interactions with them only occurred on 20% of these occasions and were mostly initiated by the heterospecifics. The two main antagonists are not closely related to, and their diets overlap little with that of Galahs, and the interactions only marginally affected the latter’s foraging efficiency. We concluded that: (i) Galahs appeared inherently suited for urban foraging without much behavioural adjustment being required, and (ii) direct interference competition for food with other resident bird species was probably not a significant influence on Galahs’ persistence in the urban environment.
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