Odette Curtis

Black Harrier Circus maurus of the Fynbos biome, South Africa: a threatened specialist or an adaptable survivor?

Black Harrier Circus maurus is a rare southern African endemic that may have lost over 50% of its core breeding habitat in the last century as a result of extensive land transformation by agriculture, invasive alien vegetation and urbanization in the Fynbos biome. We partially surveyed both the western (Swartland) and southern (Overberg) coastal plains of south-western South Africa, over 3 years (2000–2002) for breeding Black Harriers, and found a distinctly polarized distribution. Nests were concentrated either along the coastal strip or inland in montane habitats, and generally absent from heavily cultivated and transformed inland plains areas. Limited evidence (direct observations, prey remains) suggests that harriers forage in cereal croplands but generally do not breed in these modified environments. We recorded breeding success at nests in coastal (Dune Thicket) and montane (Mountain Fynbos) habitats. Harriers bred successfully along the coast and nests were aggregated in loose colonies around wetlands. Harriers in montane environments bred poorly, took a wide range of prey, and were subject to high levels of nest predation. We propose that Black Harriers have been displaced from lowland Renosterveld and Fynbos habitats (characterized by better foraging and nesting opportunities), primarily by the advent and spread of cereal agriculture. The conservation and future research implications of this hypothesis are discussed.

Fidelity at the frontier: divorce and dispersal in a newly colonized raptor population

Divorce and breeding dispersal are key life history parameters that can be influenced by, and in turn have an influence on, the structure of populations. Variation in these parameters in small populations can potentially play an important role in the colonization of new areas, yet to date there has been little empirical investigation of this process. We studied the circumstances surrounding divorce in a newly established population of black sparrowhawks, Accipiter melanoleucus, on the Cape Peninsula, South Africa over an 11-year period between 2001 and 2012. Divorce was more likely following breeding failure and individuals that divorced and dispersed improved their subsequent breeding success. Territory quality had no influence on the frequency of divorce, and dispersing individuals did not move to territories of higher quality. During the study period the population size increased approximately three-fold, but because the range expanded, nest density did not increase significantly. In the first half of the study (2001–2006), divorce rates were low (4%) compared with rates previously reported for raptors and other birds. In the latter half (2007–2012) divorce rates were 14%. Although there was weak support for a difference in divorce rates between these two periods there was no evidence that divorce rates varied with population size or nesting density. Our results suggest that adaptive hypotheses (‘better option’ or ‘incompatibility’) best explain patterns of divorce in this expanding population and that potential feedbacks between divorce and population processes were unlikely to have played an important role during the growth of this recently established population.

The value of the Black Harrier Circus maurus as a predictor of biodiversity in the plant-rich Cape Floral Kingdom, South Africa

Determining the efficacy of using indicator species to predict the spatial location of biodiversity hotspots is one way of maximising the conservation of biodiversity in already threatened habitats. Recent evidence from Europe suggests raptors can play such an indicator role, so we tested this approach with a globally threatened southern hemisphere species, the Black Harrier Circus maurus. We asked if this species, found in South Africa’s mega-diverse Cape Floral Kingdom, breeds in habitat fragments that were more diverse in terms of small mammals, birds and plants than unoccupied fragments of similar size. Renosterveld is a highly fragmented habitat that has lost . 90% of its original extent and remains only on privately-owned lands. Surveys of small mammals, birds and plants undertaken in 20 fragments in the Overberg region, South Africa, revealed nine with breeding harriers and 11 without harriers. Harrier-occupied fragments were associated with a 3.5 fold higher number of bird species and higher small mammal species richness than unoccupied ones. There was a lower abundance of most plants in occupied patches, except for red grass Themeda triandra which is an indicator of pristine renosterveld. Vegetation structure was significantly different, with harriers nesting on patches with taller, more open vegetation. While the diversity trends were not statistically significant, a positive trend between the presence of harriers and higher abundance of red grass – as an indicator of the more pristine state of the patch, suggests that harriers might allow biodiversity managers a heuristic approach for selecting the remaining patches of pristine renosterveld. The need for intensive sampling of several taxa leads to small samples and a lack of clear-cut trends for these top predators as indicators of plant diversity.

Negative effect of mite (Knemidokoptes) infection on reproductive output in an African raptor

ABSTRACT Knemidokoptes is a genus of subcutaneous mites found in the skin of multiple avian hosts, although few cases have been reported in wild raptors. Population monitoring of Black Sparrowhawks (Accipiter melanoleucus) on the Cape Peninsula, South Africa, between 2001 and 2012 revealed multiple birds with infection symptoms in some years. Examination of 3 dead birds displaying symptoms such as baldness and skin lesions confirmed infection by Knemidokoptes spp., whereas we found no cases of subclinical infection in birds without symptoms (n = 16). Up to 5% of birds in the population were infected in some years, which represents the first record of multiple birds displaying an infection by Knemidokoptes in a wild population of raptors. A male bias in infection prevalence was detected. Prevalence of infection symptoms was generally low in other populations elsewhere in South Africa, although possibly higher in urban areas. Breeding performance (both productivity and nesting success) was significantly lower for individuals following infection and also in comparison with noninfected birds throughout the study period. This is the first study to demonstrate the negative effect that these mites may have on breeding performance in a wild bird species, and our results suggest that this parasite could potentially influence population dynamics over time.