Du Plessis M A, Siegfried W R, Armstrong A J
Fritz Patrick Institute of African Ornithology, University of Cape Town, 7700, Rondebosch, South Africa.
Department of Nature Conservation, Forestry Faculty, University of Stellenbosch, 7600, Stellenbosch, South Africa.
Oecologia. 1995 May;102(2):180-188. doi: 10.1007/BF00333250.
Our analyses of the incidence of cooperative breeding among South African birds differ from previous studies performed elsewhere in two respects. First, we distinguish between "obligate" (i.e. regular) and "facultative" (i.e. opportunistic) cooperative breeding species (OCS and FCS). Second, we have restricted our analyses to 217 South African bird species considered to be sufficiently well-studied in terms of their basic biology and life-history characteristics. This was done in order to control for the well-known bias against the often poorly-studied avifaunas of extreme environments such as rainforests and deserts. The results of our analysis do not accord fully with those of Australian birds by Ford et al. (1988). Cooperative breeding in South Africa is associated with seasonal environments, whereas in Australia the opposite is the case. Analyses of ecological factors that promote cooperative breeding among South African birds suggest that the evolutionary pathway to obligate and facultative breeding may be fundamentally different. First, OCS live mainly in savanna habitats that have predictable seasonal peaks in food availability, yet where the baseline level of food availability during the nonbreeding season is sufficient to support permanent residence by groups. Small to medium-sized birds of the African savannas are particularly vulnerable to avian predators, and foraging and roosting in permanent groups may enhance their survival. We propose that the benefits of obligate cooperative breeding are derived chiefly from survival of individuals away from the nest (i.e. during the nonbreeding season). Secondly, FCS live largely in unpredictable, seasonal steppe habitats. Under these conditions it may be impossible for birds to maintain permanent group territories, and variation in the tendency to breed cooperatively may depend largely on the opportunistic assessment of environmental conditions. We therefore suggest that birds (i.e. FCS) will opt to breed cooperatively only when conditions are unfavourable for independent breeding, and that the benefits thus accrued are chiefly related to reproduction.
我们对南非鸟类合作繁殖发生率的分析在两个方面与之前在其他地方进行的研究不同。首先，我们区分了“ obligate”（即常规的）和“ facultative”（即机会主义的）合作繁殖物种（OCS和FCS）。其次，我们将分析限制在217种南非鸟类上，这些鸟类在其基本生物学和生活史特征方面被认为有充分的研究。这样做是为了控制对热带雨林和沙漠等极端环境中通常研究不足的鸟类群落的众所周知的偏见。我们的分析结果与福特等人（1988年）对澳大利亚鸟类的分析结果并不完全一致。南非的合作繁殖与季节性环境有关，而在澳大利亚则相反。对促进南非鸟类合作繁殖的生态因素的分析表明，向 obligate和facultative繁殖的进化途径可能有根本的不同。首先，OCS主要生活在热带稀树草原栖息地，那里食物供应有可预测的季节性高峰，但非繁殖季节的食物供应基线水平足以支持群体永久居住。非洲热带稀树草原上的中小型鸟类特别容易受到鸟类捕食者的攻击，在永久群体中觅食和栖息可能会提高它们的生存几率。我们认为， obligate合作繁殖的好处主要来自个体在巢外（即非繁殖季节）的生存。其次，FCS主要生活在不可预测的季节性草原栖息地。在这些条件下，鸟类可能无法维持永久的群体领地，合作繁殖倾向的变化可能在很大程度上取决于对环境条件的机会主义评估。因此，我们建议鸟类（即FCS）只有在不利于独立繁殖的条件下才会选择合作繁殖，由此获得的好处主要与繁殖有关。
