Browsing by Subject "body condition"

Now showing 1 - 3 of 3
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    Open Access
    Further investigation of whether correlations amongst data are invalidating the conclusion of a statistically significant trend in Antarctic minke body condition over time
    (2013) Konishi, K; Butterworth, Doug S
    A statistically significant decline in body condition in the Antarctic minke whale over the JARPA period was reported in Konishi et al. (2008). Subsequently, however, questions were raised in the IWC Scientific Committee as to whether the model used had adequately accounted for the data structure in JARPA (de la Mare, 2011), i.e. whether neglect of correlations in the data had led to negative bias in the confidence interval estimated for the decline. Earlier a jack-knife approach with year as the sampling unit was used to account for within-year correlations, and showed that while the confidence interval estimates reported originally had been negatively biased, the estimated decline remained statistically significant at the 5% level. This approach did not, however, take account of possible betweenyear correlations. This paper investigates the possibility that such correlations could have biased these interval estimates appreciably. The results show no sign of appreciable interannual auto-correlation, and indicate that the decline reported by Konishi et al. (2008) remains statistically significant at the 5% level. We suggest that his constitutes sufficient statistical evidence to confirm this significance, so that this matter might now be regarded as resolved by the Scientific Committee.
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    Open Access
    How does urbanisation affect the breeding performance of African Crowned Eagles (Stephanoaetus coronatus)?
    (2019) Muller, Rebecca; Amar, Arjun; Sumasgutner, Petra; McPherson, Shane; Downs, Colleen
    Birds face many challenges from the process of urbanisation. Those species that are able to occupy urban areas offer opportunities to understand processes of acclimatisation to urban life and may help in the development of urban spaces for the benefit of wildlife. In many bird species, individuals that occupy territories in more urban areas show lower productivity and lower body condition of nestlings, which is thought to be mediated by food availability. Most of the studies exploring this issue were done on passerines and carried out in the global north, with very few studies exploring this topic on non-passerines, and even fewer in Africa. Studies addressing urban productivity in apex predators with slow life histories that are often of conservation concern are largely missing. Here, we explore the breeding performance of the African Crowned Eagles (Stephanoaetus coronatus) across an urbanisation gradient in KwaZuluNatal, South Africa. Specifically, we explored the hypothesis that living in an urban environment allows this species, which is typically a biennial breeder, to breed annually more often (i.e. increased breeding rate), and whether this might increase the productivity of this species. We also explore whether there may be any hidden costs of such a breeding strategy by examining the condition of chicks for pairs which had successfully bred in the previous year. We found that Crowned Eagles breeding in more urban areas attempted to breed more often (i.e., higher breeding rate), but that these birds also suffered from lower breeding success. These two contrasting responses counteracted each other and meant that overall productivity (number of young produced per occupied territory) was not influenced by urbanisation. Breeding annually did not appear to have a negative cost on the chick condition, as offspring in the year following a successful breeding attempt did not have lowered body condition. This species appears to be well adjusted to breeding in an urban environment. Crowned Eagles are currently considered vulnerable in South Africa, and ensuring that an urban population of this species is able to persist can help secure the conservation status of this charismatic species.
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    Open Access
    Seasonal rainfall at long-term migratory staging sites is associated with altered carry-over effects in a Palearctic-African migratory bird
    (2016) Sorensen, Marjorie C; Fairhurst, Graham D; Jenni-Eiermann, Susanne; Newton, Jason; Yohannes, Elizabeth; Spottiswoode, Claire N
    Abstract Background An understanding of year-round habitat use is essential for determining how carry-over effects shape population dynamics in long-distance migratory songbirds. The recent discovery of long-term migratory staging sites in many species, prior to arrival at final wintering sites, adds complexity to efforts to decipher non-breeding habitat use and connections between sites. We investigated whether habitat conditions during migratory staging carry over to influence great reed warbler (Acrocephalus arundinaceus) body condition at final wintering sites in Zambia. We asked whether the presence/absence and strength of such carry-over effects were modified by contrasting rainfall conditions during 2 years. Results First, we found that individuals staging in a dry year had higher corticosterone (CORT f ) and stable nitrogen isotope values (suggesting higher aridity) than birds staging in a wet year, indicating that regional weather affected staging conditions. Second, we found that carry-over effects from staging habitat conditions (measured via carbon and nitrogen isotopes) to final winter site body condition (measured via scaled mass index and β-hydroxybutyrate) were only present in a dry year, suggesting that environmental factors have consequences for the strength of carry-over effects. Our results also suggest that wet conditions at final winter sites may buffer the effects of poor staging conditions, at least in the short term, since individuals that staged in a dry year had higher scaled mass indices in Zambia than individuals that staged in a wet year. Conclusions This study provides a first insight into the connections between long-term migratory staging sites and final wintering sites, and suggests that local environmental factors can modify the strength of carry-over effects for long-distance migratory birds.