Urban areas can be attractive to certain species because of increased food abundance and nesting availability, which in turn may increase productivity or breeding rates. However, there are also potential costs associated with urban living such as higher nest failure, poorer body condition, or increased prevalence of disease. These costs may result in species trading off the number of young produced against the condition of their young. African Crowned Eagles (Stephanoaetus coronatus) are a rare example of large, powerful apex predators that breed in some urban areas in Africa. In this study, we explored the breeding performance of these eagles across an urbanization gradient in KwaZulu-Natal Province, South Africa, over 7 breeding seasons. We predicted that living in an urban environment would increase productivity through an increase in breeding rate (shifting from typically biennial breeding to annual breeding). We then explored if there were any hidden costs associated with such a change in breeding strategy by examining the body condition of chicks from pairs that had successfully bred in the previous year. We found that pairs in more urban areas were more likely to breed annually, resulting in higher breeding rates, but were also less likely to successfully fledge a chick (i.e. lower breeding success). These 2 contrasting responses counteracted each other and resulted in similar productivity across the urbanization gradient. For those eagles that bred in consecutive years, annual breeding did not appear to have a negative cost on chick condition. The switch to annual breeding is thought to be a response to improved or more constant food sources in urban areas, while higher failure rates might be because of increased nest disturbances from anthropogenic sources (e.g., vegetation clearing, development of industrial areas, human and car traffic). However, although urbanization negatively affected the breeding success of African Crowned Eagles, they are able to persist and thrive in this highly transformed environment, likely through an increased breeding rate.

中文翻译：

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在濒临灭绝的非洲冠鹰的城市人口中，城市化与提高繁殖率有关，但降低了繁殖成功率

城市地区可能对某些物种具有吸引力，因为它们增加了食物的丰度和筑巢的能力，这反过来又可以提高生产力或繁殖率。但是，还有一些与城市生活有关的潜在成本，例如更高的巢巢破坏，更差的身体状况或疾病患病率增加。这些成本可能会导致物种根据幼龄条件折衷生产的幼龄数量。非洲冠老鹰（Stephanoaetus coronatus）是在非洲某些城市地区繁殖的大型，强大的先天掠食者的稀有例子。在这项研究中，我们在南非夸祖鲁-纳塔尔省的七个繁殖季节中探索了这些鹰在城市化梯度上的繁殖性能。我们预测，生活在城市环境中将通过提高繁殖率（从通常的两年度繁殖向年度繁殖转变）来提高生产力。然后，我们通过检查前一年成功繁殖的成对小鸡的身体状况，探索了与这种育种策略改变相关的隐性成本。我们发现，更多城市地区的成年配对更可能每年繁殖，从而导致更高的繁殖率，但也不太可能成功培育雏鸡（即繁殖成功率较低）。这两个相反的反应相互抵消，并导致整个城市化梯度的生产率相似。对于那些连续几年繁殖的雄​​鹰来说，每年的繁殖似乎不会对雏鸡造成负面影响。人们认为转向年度育种是对城市地区食物来源的改善或更稳定的一种反应，而更高的失败率可能是由于人为来源（例如清除植被，工业区，人和汽车的发展）造成的巢穴干扰增加交通）。然而，尽管城市化对非洲冠鹰的繁殖成功产生了负面影响，但它们仍能够在这种高度变化的环境中保持生存和繁衍，这很可能是通过提高繁殖率来实现的。