Department of Biological Sciences, Macquarie University, Sydney, New South Wales 2109 Australia.
Ecology. 2013 Feb;94(2):325-35. doi: 10.1890/12-0572.1.
The foraging benefits of coloniality, whereby colony members exchange information about food location, have been suggested as a primary factor influencing the evolution of coloniality. However, despite its longstanding popularity, this hypothesis has rarely been tested experimentally. Here, we conducted a field experiment in the wild Zebra Finch Taeniopygia guttata to test whether colonial birds are better at finding food than solitary individuals. We manipulated food patch location and directly measured foraging activity of many colonial and solitary parents at those patches using an electronic monitoring system. We provided nesting sites in excess to alleviate nest site competition and manipulated brood size to eliminate the possible correlation between brood size, nesting density, and individual quality (including foraging activity). We found that solitary birds found experimental food patches first, closely followed by colonial birds. Moreover, solitary parents adjusted the amount of food per nestling to experimental brood size, whereas colonial parents did not, although overall, nestlings were fed more per capita in colonial than in solitary nests. In addition, brood size and, to a lesser extent, nesting density negatively affected nestling growth. Therefore, with the effect of provisioning rate, sibling competition, and cost of coloniality combined, nestling mass was not affected by the brood manipulation in solitary nests, whereas nestlings were lighter in enlarged than in reduced broods in colonies. Our resultstherefore suggest that individuals settling in solitary nests were intrinsically better foragers and more optimal parents. While they do not invalidate the possibility of information transfer at colonies, our findings highlight the importance of considering settlement bias in future studies and add to the existing evidence that the effects of nesting density on fitness are both complex and multiple.
群居的觅食优势，即群体成员交换食物位置的信息，被认为是影响群居进化的主要因素。然而，尽管这个假设由来已久，但它很少被实验验证。在这里，我们在野外的斑马雀 Taeniopygia guttata 中进行了一项现场实验，以测试群居鸟类是否比独居个体更擅长寻找食物。我们操纵了食物斑块的位置，并使用电子监测系统直接测量了许多群居和独居亲鸟在这些斑块上的觅食活动。我们提供了多余的筑巢地点，以缓解筑巢地点的竞争，并操纵了巢内雏鸟的数量，以消除巢内雏鸟数量、筑巢密度和个体质量（包括觅食活动）之间的可能相关性。我们发现，独居鸟类首先发现了实验性的食物斑块，其次是群居鸟类。此外，独居亲鸟根据实验巢内雏鸟的数量来调整每只雏鸟的食物量，而群居亲鸟则没有，尽管总体而言，群居巢穴中每只雏鸟的喂养量高于独居巢穴。此外，巢内雏鸟的数量以及筑巢密度在一定程度上，对雏鸟的生长产生负面影响。因此，考虑到喂养率、兄弟姐妹竞争和群居成本的综合影响，在独居巢穴中，巢内雏鸟的数量不会影响雏鸟的生长，而在扩大的巢中，巢内雏鸟比在缩小的巢中轻。因此，我们的结果表明，选择独居巢穴的个体本质上是更好的觅食者和更优的亲代。虽然这并没有否定群居时信息传递的可能性，但我们的研究结果强调了在未来的研究中考虑定居偏差的重要性，并为现有的证据增加了一点，即筑巢密度对适应性的影响是复杂和多样的。
