Investigating the effects of environmental variables on martial eagle breeding performance in the Kruger National Park - MSC Data.

Within South Africa martial eagles reporting rates have decreased by almost
60% over the last 2 decades. Similar declines have also been reported within
Kruger National Park (KNP), which is regarded as a stronghold for this species.
Declines within KNP have been attributed to the low productivity rates. As apex
predators, marital eagles are considered to be good indicators of ecosystem
health, being sensitive to the cumulative effects of disturbance down the food
chain. Changes in the breeding performance of martial eagles may therefore
indicate broader environmental change within the ecosystem. In this study, we
aim to explore which environmental variables (e.g. climate, land cover, tree
cover, fire and elephant abundance) within each territory correlated with martial
eagle breeding performance in the hope that we may better understand which variables
affect martial eagles breeding performance and whether these may have changed
over time to cause the low levels of fecundity presently seen within KNP. We found
that breeding productivity (young per territorial pair) was positively
influenced by higher precipitation and Normalized Difference Vegetation Index (NDVI)
and negatively impacted by high temperatures during the previous year. Breeding
rate (breeding attempt per territorial pair) appeared to be negatively
influenced by higher tree cover within 6km of the nest site. Nesting success
(outcome of a breeding attempt) was correlated with higher NDVI and lower
relative levels of precipitation during the previous year. Using longer term
climatic data and the relationship between climate in the previous year and
productivity, (the variable which directly relates to annual fecundity), we hindcast
the predicted productivity over the last 3 decades (2018-1986) to explore
whether change in climate conditions (precipitation, temperature and NDVI)
might reveal declines in productivity. No such declines were predicted, thus,
our results do not explain why productivity has declined within KNP.

在南非，过去二十年中，猛禽的报道率下降了近60%。类似的下降趋势也出现在克鲁格国家公园（KNP），该公园被视为这一物种的巩固地。KNP内的下降归因于低生产力。作为顶级捕食者，猛禽被认为是生态系统健康的良好指标，对食物链中累积干扰的累积效应敏感。因此，猛禽繁殖表现的变化可能表明生态系统内更广泛的环境变化。在本研究中，我们旨在探究每个领地内哪些环境变量（例如气候、土地覆盖、树木覆盖、火灾和象群密度）与猛禽的繁殖表现相关联，以期更好地理解哪些变量影响猛禽的繁殖表现，以及这些变量是否随时间变化导致克鲁格国家公园目前所见的低繁殖力。我们发现，繁殖生产力（每个领地对繁殖的幼鸟数量）受到更高降水量和归一化植被指数（NDVI）的积极影响，而前一年的高温则对其产生负面影响。繁殖率（每个领地对繁殖尝试的次数）似乎受到巢穴6公里范围内更高树木覆盖率的负面影响。巢穴成功率（繁殖尝试的结果）与更高的NDVI和前一年相对较低的降水量相关。通过使用更长期的气候数据和前一年气候与生产力（直接影响年度繁殖力的变量）之间的关系，我们回溯预测了过去三十年（1986-2018）的预测生产力，以探究气候变化条件（降水量、温度和NDVI）的变化是否可能揭示生产力的下降。没有预测到这样的下降，因此，我们的结果无法解释为什么克鲁格国家公园的生产力会下降。