Spatial patterns of extra-pair paternity for spotted towhees (Pipilo maculatus) in urban parks

The extra-pair (EP) mating system of birds may be influenced by food resources, such that nutritionally stressed females are unable to pursue EP fertilizations (constrained female hypothesis; CFH), or that females on poor territories acquire EP fertilizations during extra-territorial forays in search of food (mating opportunity hypothesis; MOH). Edges of urban habitat fragments are sites of apparent high food abundance for spotted towhees (Pipilo maculatus), and we used distance to habitat edge in four urban parks in Portland, OR, USA (2004-2006), to test the CFH and MOH. EP paternity was independent of park identity and year; 44% of nests contained EP young and 26% of all young were EP. As predicted by the CFH, EP paternity was more common in nests of long-tailed (presumably) high quality females. However, independently of tail length, younger females had more EP young than older females, a finding consistent with the MOH. Contrary to predictions of both hypotheses, the probability tha...

鸟类的配对外交配（extra-pair, EP）系统可能受到食物资源的调控：一类观点认为营养胁迫的雌性个体无法进行配对外受精（受限雌鸟假说（constrained female hypothesis, CFH)）；另一类观点则提出，栖息于劣质生境领域的雌性在开展领域外觅食活动的过程中，可获得配对外受精的机会（交配机会假说（mating opportunity hypothesis, MOH)）。城市生境片段的边缘区域是斑唧鹀（Pipilo maculatus）食物丰度显著较高的觅食场所，我们以美国俄勒冈州波特兰市四座城市公园（2004-2006年）中各巢址与生境边缘的距离为变量，对CFH与MOH展开了检验。研究结果显示，配对外父权（extra-pair paternity, EP父权）与公园属性及调查年份均无显著关联：44%的巢内存在配对外幼鸟，且所有统计幼鸟中有26%为配对外幼鸟。正如CFH的预测，长尾（推测为高质量）雌性的巢中，配对外父权现象更为普遍。然而，在控制尾长变量的前提下，年轻雌性的巢内配对外幼鸟数量显著多于年长雌性，这一结果与MOH的预测相符。与两种假说的预测均相悖的是，……