Accipiter Melanoleucus Research Articles

Is multiple nest building an adequate strategy to cope with inter-species nest usurpation?

BackgroundBlack sparrowhawks (Accipiter melanoleucus) recently colonised the Cape Peninsula, South Africa, where the species faces competition for their nest sites from Egyptian geese (Alopochen aegyptiaca) which frequently usurp black sparrowhawk nests. In this paper, we test the hypothesis that multiple nest building by black sparrowhawks is a strategy to cope with this competitor, based on a 14-year long term data set.ResultsTwo main results support the hypothesis: first, the numbers of intact nests per breeding season in black sparrowhawk territories increased as levels of geese interactions increased, specifically when usurpation occurred. Usurpation occurred significantly more often at nests later in the season, and may provide a further explanation for the advancement of the black sparrowhawk breeding season towards earlier breeding attempts which results in an overall extension of the breeding period (over 9 months) that has been found in our study population. Second, nest usurpation had a negative impact on black sparrowhawks’ reproductive performance at the ‘nest’ level, but not at the ‘territory’ level when multiple nests were available within the same breeding season, suggesting that this strategy was effective for dealing with this competitor. However, our results do not rule out long term negative consequences of these interactions, for example, reduced adult survival rates or reduced lifetime reproductive success, due to the higher energy demand required to build several nests each breeding season.ConclusionsOur results suggest that black sparrowhawks avoid direct conflict with this large and aggressive competitor and instead choose the passive strategy in allocating more resources to multiple nest building. Our research further highlights the importance of behavioural plasticity, which might be especially important for city-dwelling species in the face of global urbanisation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0671-7) contains supplementary material, which is available to authorized users.

Differential foraging success across a light level spectrum explains the maintenance and spatial structure of colour morphs in a polymorphic bird.

Detectability of different colour morphs under varying light conditions has been proposed as an important driver in the maintenance of colour polymorphism via disruptive selection. To date, no studies have tested whether different morphs have selective advantages under differing light conditions. We tested this hypothesis in the black sparrowhawk, a polymorphic raptor exhibiting a discrete white and dark morph, and found that prey provisioning rates differ between the morphs depending on light condition. Dark morphs delivered more prey in lower light conditions, while white morphs provided more prey in brighter conditions. We found support for the role of breeding season light level in explaining the clinal pattern of variation in morph ratio across the species range throughout South Africa. Our results provide the first empirical evidence supporting the hypothesis that polymorphism in a species, and the spatial structuring of morphs across its distribution, may be driven by differential selective advantage via improved crypsis, under varying light conditions.

Family morph matters: factors determining survival and recruitment in a long-lived polymorphic raptor.

From an evolutionary perspective, recruitment into the breeding population represents one of the most important life-history stages and ultimately determines the effective population size. In order to contribute to the next generation, offspring must survive to sexual maturity, secure a territory and find a mate. In this study, we explore factors influencing both offspring survival and their subsequent recruitment into the local breeding population in a long-lived urban raptor, the black sparrowhawk (Accipiter melanoleucus). Adult black sparrowhawks show discrete colour polymorphism (dark and light morphs), and in South Africa, morphs are distributed clinally with the highest proportion of dark morphs (c.75%) present in our study population on the Cape Peninsula. Parental morph was associated with both survival and recruitment. For survival, parental morph combination was important - with young produced by pairs of contrasting morphs having higher survival rates than young fledged from like-pairs. The association between recruitment and morph was more complex; with an interaction between male morph and breeding time, whereby recruitment of offspring from dark morph fathers was more likely when fledging earlier in the season. The opposite relationship was found for light morph fathers, with their offspring more likely to be recruited if fledged later in the season. This interaction may be due to differential morph-specific hunting success of fathers (males contribute most food provisioning), linked to background matching and crypsis in different weather conditions. Dark morph males may hunt more successfully in rainier and cloudier conditions, which occur more frequently earlier in the breeding season, and light morph males may be more successful later on, when weather conditions become increasingly brighter and drier. Our results reveal a complex situation whereby the family morph combination influences survival, and the father morphs specifically recruitment, revealing morph-specific benefits dependent on the timing of breeding. These empirical data are among the first to support the idea that differential fitness consequence of morph combination may explain balanced polymorphism in a vertebrate population.

Black Sparrowhawk brooding behaviour in relation to chick age and weather variation in the recently colonised Cape Peninsula, South Africa

Understanding the effects climate change may have on animal populations relies on establishing which environmental conditions shape their behaviour and subsequent reproductive output, fitness or survival. South Africa has seen significant warming trends and changes in precipitation over the last few decades; however, the ways in which these trends are likely to influence animal populations are still relatively poorly understood. The Black Sparrowhawk (Accipiter melanoleucus) has expanded its range in South Africa and recently colonised the Cape Peninsula in the Western Cape, a region that experiences a Mediterranean climate. In this study, we examined the brooding behaviour of this species, a vital trait for reproductive success, in the Cape Peninsula breeding population. We examined the influence of chick age as well as temperature, rainfall and wind speed on parental brooding. Additionally, the effect of prey provisioning on brooding was investigated. In our analyses, we used data on brooding from nest cameras together with weather data collected at a fine temporal scale (1 h). The variable with the strongest influence on parental brooding was chick age. This variable showed a non-linear relationship. Initially chicks were brooded >50 % of the time; however after 3 weeks brooding declined rapidly. The proportion of time spent brooding increased with decreasing temperatures, while rainfall and wind speed showed a positive correlation with the amount of brooding. Our model predicted that in common winter conditions of the Western Cape (15 °C, 10 km/h wind speed, 1 mm/h rainfall) A. melanoleucus breeding pairs spent nearly 100 % of their time brooding young chicks (7 days old) to protect them from detrimental weather. Our results highlight measurable effects of weather patterns on avian behaviour at a key stage of the life cycle. Changes in weather conditions predicted for this region will likely further benefit this range-expanding species.

Phenological shifts assist colonisation of a novel environment in a range‐expanding raptor

In a rapidly changing world understanding the capacity of populations to adapt to novel environments is increasingly urgent. Timing of breeding can be a highly flexible trait and adjustments in this trait can potentially buffer populations from climate change and facilitate the colonisation of new environments. Recent range‐expansions into novel climatic regimes provide a valuable opportunity to investigate the implications of plasticity in timing of breeding for population processes. Black sparrowhawks have recently colonised the Cape Peninsula of South Africa where they experience dramatically different weather patterns to those in their historical range. These include a total reversal in the rainfall regime, with the majority of rain falling in the winter as opposed to the summer months. We investigate the breeding phenology of black sparrowhawks in relation to both regional and local climate variation and, using a long‐term dataset, explore the implications of phenological shifts for reproductive success and population growth following colonisation. In the recently colonised Cape Peninsula the breeding season began up to three months earlier than within their historical range and these early breeding attempts produced more offspring. Population models suggested that this adjustment assisted the colonisation of the Cape Peninsula, reducing the probability of extinction by 23%. Contrary to expectations, we found little support for the hypothesis that black sparrowhawks were responding to local variation in rainfall. We suggest that shifts in breeding phenology may be driven in part by other novel processes, such as interspecific competition for nest sites and lower temperatures during late summer. These results provide insight into the processes that facilitated the colonisation of a novel climatic regime highlighting the potential role of a diverse range of factors.

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.

Clinal variation in the morph ratio of Black Sparrowhawks Accipiter melanoleucus in South Africa and its correlation with environmental variables

The morph ratio distribution in polymorphic species often varies clinally, with a gradual change in morph ratios across the distributional range of the species. In polymorphic bird populations, clinal variation is rarely quantified. We describe a cline in the morph ratios of Black Sparrowhawks across South Africa, which is principally driven by a higher ratio of dark morph birds in the newly colonized southwest of the country. Across the 1400 km of our cline, the probability of a bird being a dark morph declined from over 80% close to the Cape Peninsula to under 20% in the northeast. Higher frequencies of dark morphs were associated with a higher proportion of rainfall falling during the winter breeding months. Further investigation revealed relationships between the proportion of dark morphs and altitude, amount of rainfall during the breeding months, and an interaction between this variable and temperature. These results provide some support for the suggestion that the higher frequency of dark morphs in the southwest is an adaptive response, rather than the result of a founder effect or genetic drift. These findings also suggest that, in theory, polymorphic species may be better adapted to cope with the challenges of climate change or may be able to expand their ranges more quickly into novel climatic areas, since selection pressure can act on a pre‐existing trait that may be beneficial in new conditions.

Differential Haemoparasite Intensity between Black Sparrowhawk (Accipiter melanoleucus) Morphs Suggests an Adaptive Function for Polymorphism

Recent research suggests that genes coding for melanin based colouration may have pleiotropic properties, in particular conveying raised immune function. Thus adaptive function of polymorphism may be associated with parasite resistance. The black sparrowhawk Accipiter melanoleucus is a polymorphic raptor with two morphs. Over most of its range the light morph is commonest, however within the recently colonised Western Cape of South Africa the dark morph predominates. The species breeds in winter throughout South Africa, however unlike in the rest of the species' South African range, the Western Cape experiences a winter rainfall regime, where arthropod vectors which transmit haematozoan parasites may be more abundant. We hypothesise that the higher frequency of dark morph birds in this region may be due to their improved parasite resistance, which enables them to cope with higher parasite pressure. If so, we predict that dark morph black sparrowhawks would have lower parasite burdens than light morph birds. Within our population the prevalence of the two most common haematozoan parasites was high, with 72% of adults infected with Haemoproteus nisi and 59% of adults infected with Leucocytozoon toddi. We found no difference in prevalence for either parasite between adult morphs, or between chicks of different parental morphs. However, within adults infected with H. nisi, infection intensity was significantly higher in light morphs than dark morphs. This suggests that dark morphs have lower parasite loads than light morphs due to resistance rather than morph-specific habitat exploitation. Greater resistance to Haemoproteus parasites may therefore be one of the mechanisms through which dark morph black sparrowhawks have a selective advantage in this region and may explain why they are most common in our study area. In other regions, the cost to benefit ratio may be in favour of the light morph, where parasites are less abundant or virulent.

Plumage polymorphism in a newly colonized black sparrowhawk population: classification, temporal stability and inheritance patterns

AbstractPersistent plumage polymorphism occurs in around 3.5% of bird species, although its occurrence is not distributed equally across bird families or genera. Raptors show a disproportionately high frequency of polymorphism, and among raptors it is particularly frequent among theAccipiterhawks. However, no systematic study of polymorphism in this genus exists. Using a long‐term study of the black sparrowhawk (Accipiter melanoleucus), a widespread polymorphicAfricanAccipiter, we first demonstrate that the species shows discrete polymorphism (cf. continuous polymorphism), occurring as either dark or light morph adults, and that morph type and plumage pattern are invariant with age. We then demonstrate that adult morph type follows a typicalMendelian inheritance pattern, suggesting a one‐locus, two‐allele system within which the allele coding for the light morph is dominant. This inheritance pattern provides further support for classifying polymorphism in this species as discrete. In most of the species' range the dark morph is the rarer morph; however, in our study population where the species is a recent colonist, over 75% of birds were dark and this remained fairly constant over the 10 years of our study. This reversal in morph ratio may represent an adaptive response to different environmental conditions or could be a founder effect with colonizing individuals having been mostly dark morph birds simply by chance. The extreme differences in environment conditions (seasonality of rainfall) that occur across the species' range inSouthAfrica provide support for an adaptive explanation, but further work is needed to test this hypothesis.

Use of Basic Biological Information for Rapid Prediction of the Response of Species to Habitat Loss

Much research has focused on identifying traits that can act as useful indicators of how habitat loss affects the extinction risk of species, and the results are mixed. We developed 2 simple, rapid-assessment models of the susceptibility of species to habitat loss. We based both on an index of range size, but one also incorporated an index of body mass and the other an index combining habitat and dietary specialization. We applied the models to samples of birds (Accipitridae and Bucerotidae) and to the lemurs of Madagascar and compared the models' classifications of risk with the IUCN's global threat status of each species. The model derived from ecological attributes was much more robust than the one derived from body mass. Ecological attributes identified threatened birds and lemurs with an average of 80% accuracy and endangered and critically endangered species with 100% accuracy and identified some species not currently listed as threatened that almost certainly warrant conservation consideration. Appropriate analysis of even fairly crude biological information can help raise early-warning flags to the relative susceptibilities of species to habitat loss and thus provide a useful and rapid technique for highlighting potential species-level conservation issues. Advantages of this approach to classifying risk include flexibility in the specialization parameters used as well as its applicability at a range of spatial scales.

Competition with Egyptian Geese Alopochen aegyptiaca overrides environmental factors in determining productivity of Black Sparrowhawks Accipiter melanoleucus

We studied a population of Black Sparrowhawks Accipiter melanoleucus that has recently colonized the Cape Peninsula, South Africa. Black Sparrowhawks are winter breeders: over most of their range winters are dry, but the Cape Peninsula has a Mediterranean climate, with most rain falling in winter. The birds bred at an average density of 38 pairs/100 km2. Monitoring of 70 breeding attempts by 26 pairs showed that the birds favoured large stands of trees for breeding. Birds breeding in smaller stands were more randomly spaced, dispersion being determined by habitat availability. Parameters related to climate, habitat and aspects of nest‐site selection failed to predict the birds’ productivity despite the fact that they had recently colonized a novel climatic window. Rather, productivity was best explained by the probability of nest usurpation by highly aggressive Egyptian Geese Alopochen aegyptiaca. Pairs encountering Goose usurpation problems raised an average of 0.76 chicks per breeding attempt, compared with 1.58 chicks for pairs without Geese. The only defence against nest usurpation by Geese appears to be the construction of multiple nests, an option most available to and most exploited by birds breeding in large stands of trees.

Comparative biology of the forest-inhabiting hawks Accipiter spp. in the Democratic Republic of Congo

The four Accipiter species in the equatorial forest of the Democratic Republic of Congo (from small to large: Red-thighed Sparrowhawk A. erythropus, Chestnut-flanked Sparrowhawk A. castanilius, African Goshawk A. (tachiro) toussenelii and Black Sparrowhawk A. melanoleucus) were studied in the field, as to crop and stomach contents, fat storage, and behaviour. Museum specimens (in the Royal Museum for Central Africa, Belgium) were also examined for the purpose of studying morphometry, sex- and age ratios, and moult. Insects, amphibians, reptiles and mammals were found in the crops and stomachs of the three smallest species, but no birds were found, which is surprising and perhaps due to poor identification prospects. The variation in prey demonstrates the large diet; ecological separation between species must be based mainly on behavioural differences. Storage of fat in adult females (perhaps in the pre-breeding phase) and in immature birds was discovered, an unexplained event in a resident tropical species. Because photographs of the Chestnut-flanked Sparrowhawk show its relatively large eyes, suggesting an adaptation to living in dense forest, morphometry of the skull was done, showing that it is proportionally broader in this species than in the African Goshawk. Males of Black Sparrowhawk, females of African Goshawk, adult males of Red-thighed Sparrowhawk, and juvenile females of Chestnut flanked Sparrowhawk are more common in the collection than the opposite sex (in each case). These unequal sex ratios between species, some statistically significant, could be due to behavioural differences. Although annual primary moult is descendant in most specimens, it is demonstrated here for the first time in the genus Accipiter (in the African Goshawk) that it does not always follow a strict descendant mode. Some serial descendant primary moult cases are illustrated. They could indicate breeding in rapid sequence, which is not unexpected in tropical regions without marked seasons. But the cases of asymmetrical moult are less easily explained; perhaps these involve replacement of feathers after accidental loss.

Moult, pied plumage and relationships within the genus of the Black Sparrowhawk Accipiter melanoleucus

The pied plumage of the adult Black Sparrowhawk is rather exceptional in the genus Accipiter and it could be explained by functionality or by phylogenetic relationships. The moult pattern of museum specimens is presented, supplementing information from captive birds. The post-juvenile moulting sequence is similar to that of the Northern Goshawk. The moult of primaries starts at, or just after, the beginning of body moult; moult of the secondaries also starts early and progresses from three consecutive foci, and tail moult starts early but is less predictable. A few body feathers and tail feathers may remain in place until the second moult. The pied flank feathers appear at an early stage. Some adult specimens are in arrested annual moult. Two with definite serially-descendant moult were discovered; this is related to the fact that the species is known to be double-brooded. Serially descendant moult was not known in this species and is rarely mentioned in the genus. Possible functions of the pied plumage are discussed: crypsis, mimicry, hunting strategy, and sexual attraction. Its taxanomic status is obscure. Although the streaked juvenile plumage of the Black Sparrowhawk is similar to those of the Northern Goshawk A. gentilis, Meyer's Goshawk A. meyerianus and Henst's Goshawk A. hentsi, adult and juvenile plumages are variable within the genus, and thus are not a reliable indicator of taxanomic relationships.

Multiple‐brooding in birds of prey: South African Black Sparrowhawks Accipiter melanoleucus extend the boundaries

Multiple‐brooding (raising more than one brood of young in quick succession) occurs infrequently in raptors and is generally restricted to either smaller species with shorter nesting periods, co‐operative breeders or species capable of capitalizing on conditions of prolonged food abundance whenever they occur. This paper presents the first recorded cases of multiple‐brooding in the Black Sparrowhawk Accipiter melanoleucus from two distinct locales in South Africa. In the Western Cape (Cape Peninsula), four attempts to multiple‐brood were recorded in four different years, involving three distinct pairs of birds, and in KwaZulu–Natal (Eshowe), three distinct pairs of Sparrowhawks successfully multiple‐brooded on several occasions over a 5‐year study period. These results establish the Black Sparrowhawk as one of only two relatively large, monogamous raptor species, and the only specialist bird‐eating raptor, in which multiple‐brooding has been recorded with any frequency. The species’ capacity to thrive in human‐modified environments (i.e. alien plantations) and particularly to exploit associated foraging opportunities (e.g. high densities of doves and pigeons in suburban areas) may, at least partly, account for the instances of multiple‐brooding reported here. We suggest that biologists be more vigilant for cases of multiple‐brooding in raptors, as it is possible that this trait is more common than originally thought and has previously been overlooked.

Nest-Site Selection by black sparrowhawks Accipiter melanoleucus: implications for managing exotic pulpwood and sawlog forests in South Africa.

This study provides timber growers with silvicultural guidelines for establishing and maintaining nest-tree habitat for native black sparrowhawks (Accipiter melanoleucus) in commercial planted forests in South Africa. In this country, exotic eucalypts and pines are planted principally for pulpwood and sawlog production. Nineteen nests were sampled in indigenous forests and 58 nests in exotic forests. Although mean nest heights differed between indigenous and exotic trees, in all trees, nests were positioned, on average, at 64% of tree height. Black sparrowhawks nested near stand edges, probably seeking a compromise between nesting adjacent to open hunting habitat and selecting an insulated tree from within the forest. Black sparrowhawks nested in tall trees ( X- = 18-33 m for different tree species classes) with a large diameter (>60 cm). Unfortunately, the South African pulpwood and sawlog industry employ short rotations (<16 years) and high tree densities (>700 trees/ha) that do not allow the trees to attain the characteristics suitable for black sparrowhawk nesting sites. Eucalypt and pine nest stands must be of 25 x 25 m minimum size and incorporate 10 trees at minimum heights of 21 and 18 m and diameters of 37 and 35 cm, respectively. If such nest-tree stands are set aside as islands in a sea of commercial forests, and black sparrowhawks and other forest raptors nest in them, timber growers will improve the tree-nesting raptor diversity of planted forests. If, however, these raptors prey upon species of conservation importance, the management recommendations could be reversed to limit the potential for predation.

Saving Saukenuk: How Black Hawk Won the War and Opened the Way to Ethnic Semiotics

If you went looking for traces of the Sauk village where Ma-ka-tai-me-she-kia-kiak (or Black Sparrow Hawk) was born and which, in his refusal to give it up, became the ultimate cause of the Black Hawk War in 1832 – the last Indian war east of the Mississippi – you would not find much: a few smart allusions to the great Sauk warrior on storefront signs and other such promotion gestures over on Rock Island, Iowa, but no archeological evidence at the juncture of the Rock and Mississippi rivers to suggest that the village ever existed. And yet, according to Cecil Eby, by 1790 Saukenuk was “the most imposing town in the Northwest, Indian or white, with more than 100 wickeups (many extending 60 feet in length) and from April to October inhabited by some 3,000 Sauk.” There are, however, scattered verbal signs that might draw the archeologist or historian back and forth over other tableaux of potential Sauk geography, like Sac City in Sac County, Iowa, and Black Hawk County due West of Dubuque. Then there is Prairie du Sac and Sauk City on the Wisconsin River, Wisconsin, two historically vibrant sites which novelist August Derleth turned to good use in his saga of Wisconsin. But when it comes to dealing with a defeated people who also happen to belong to the red race, the names themselves often become signs of cultural obscurantism, if not commemorative oblivion. In list form the available nomenclature amuses: Sacs, Saukies (which the Indians themselves used), Sockeys, Socks, Sacques, Saucs, Sakis. This embarrassing take-your-pick liberality clearly enough sets forth a problem of transliteration; it also evokes the more complex issue of cultural translationtout court:us/them, inside/outside, center/periphery, hegemonic culture/minority culture, structure/chaos.