Pius Sandra M, Leberg Paul L
Department of Biology, University of Southwestern Louisiana, Lafayette, LA 70504, USA Fax: (318) 482-5660; e-mail:
Oecologia. 1997 Jun;111(1):144-150. doi: 10.1007/s004420050218.
When heterospecific seabirds are part of a nesting colony, there may be less opportunity for conspecifics to come in direct contact with each other, resulting in lower intraspecific aggressiveness. To determine if individuals spend less time in aggressive behavior when nesting in conspecific rather than heterospecific groups, we compared the behavior of black skimmers (Rhynchops niger) nesting with gull-billed terns (Sterna nilotica) in three mixed species subcolonies to those of black skimmers in three single species subcolonies. In contrast to our predictions, black skimmers spent significantly less time in aggressive behaviors when nesting in single species subcolonies than when nesting with heterospecifics. Although skimmers in mixed species subcolonies tended to have more aggressive interactions with skimmers than terns, this may be a function of subcolony composition; the proportions of aggressive interactions with conspecifics were similar to the proportions of conspecifics in each subcolony. However, within the mixed species subcolonies, skimmers that nested nearer to terns were involved in aggressive interactions significantly less than skimmers that nested closer to conspecifics. Also, skimmers nested closer to their nearest neighbor when it was a gull-billed tern than when it was another skimmer. Regardless of which species they nested closest to, skimmers were more aggressive towards other skimmers than to terns within the mixed species subcolonies. Distance to nearest neighbor's nest did not differ significantly between the colony types, and did not seem to influence the duration of aggressive activity in the single species subcolonies. In the mixed species subcolonies, however, the time spent in aggressive behavior increased as the distance to nearest neighbor increased. It appears that of the several benefits that have been proposed of mixed species colonies, reduced time spent in conspecific aggression is not among them. However, within a mixed species colony, an individual can reduce time spent in aggressive interactions by nesting near heterospecifics.
当异种海鸟成为筑巢群体的一部分时，同种个体之间直接接触的机会可能会减少，从而导致种内攻击性降低。为了确定个体在同种群体而非异种群体中筑巢时是否会减少攻击行为的时间，我们将在三个混合物种亚群中与鸥嘴燕鸥（Sterna nilotica）一起筑巢的黑腹剪嘴鸥（Rhynchops niger）的行为与在三个单物种亚群中的黑腹剪嘴鸥的行为进行了比较。与我们的预测相反，黑腹剪嘴鸥在单物种亚群中筑巢时花费在攻击行为上的时间明显少于与异种一起筑巢时。虽然混合物种亚群中的剪嘴鸥与剪嘴鸥之间的攻击性互动往往比与燕鸥之间更多，但这可能是亚群组成的一个函数；与同种个体的攻击性互动比例与每个亚群中同种个体的比例相似。然而，在混合物种亚群中，靠近燕鸥筑巢的剪嘴鸥参与攻击性互动的频率明显低于靠近同种个体筑巢的剪嘴鸥。此外，当最近的邻居是鸥嘴燕鸥时，剪嘴鸥比当最近的邻居是另一只剪嘴鸥时更靠近它筑巢。在混合物种亚群中，无论它们最靠近哪种物种筑巢，剪嘴鸥对其他剪嘴鸥的攻击性都比对燕鸥更强。不同群体类型之间到最近邻居巢穴的距离没有显著差异，并且似乎也不影响单物种亚群中攻击活动的持续时间。然而，在混合物种亚群中，随着到最近邻居距离的增加，用于攻击行为的时间也增加。看来，在已提出的混合物种群体的几个好处中，减少种内攻击行为的时间并不在其中。然而，在混合物种群体中，个体可以通过在异种个体附近筑巢来减少用于攻击性互动的时间。
