| is multiple nest building an adequate strategy to cope with inter-species nest usurpation? | black 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. | 2016 | 27150363 |
| 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 c ... | 2016 | 27132885 |
| response time of an avian prey to a simulated hawk attack is slower in darker conditions, but is independent of hawk colour morph. | to avoid predation, many species rely on vision to detect predators and initiate an escape response. the ability to detect predators may be lower in darker light conditions or with darker backgrounds. for birds, however, this has never been experimentally tested. we test the hypothesis that the response time of avian prey (feral pigeon columbia livia f. domestica) to a simulated hawk attack (taxidermy mounted colour-polymorphic black sparrowhawk accipiter melanoleucus) will differ depending on l ... | 2019 | 31598248 |
| morph specific foraging behavior by a polymorphic raptor under variable light conditions. | colour polymorphism may be maintained within a population by disruptive-selection. one hypothesis proposes that different morphs are adapted to different ambient light conditions, with lighter morphs having a selective advantage in bright conditions and darker morphs having advantages in darker conditions. the mechanism for this advantage is proposed to be through enhanced crypsis via background-matching. we explore this hypothesis in a polymorphic raptor, the black sparrowhawk accipiter melanol ... | 2017 | 28831050 |
| 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 wer ... | 2001 | 11443384 |
| 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 sparrow ... | 2016 | 26990283 |
| 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 ... | 2013 | 24391707 |