Understanding the mechanism promoting polymorphism in Black sparrowhawks

Carina Nebel will present her PhD proposal, "Understanding the mechanism promoting polymorphism in Black sparrowhawks" for the Department of Biological Science seminar.

The Black sparrowhawk is a colour-polymorphic bird of prey that occurs in two colour morphs: a dark and a light morph. In the Cape peninsula, the population has been studied for 17 years and this research has resulted in several discoveries. The morphs were found to differ in prey provisioning to the nest depending on ambient light levels, indicating different hunting success, probably caused by contrasting crypsis. In an environment like the Cape peninsula that has high levels of winter rainfall (during the species’ breeding season, a highly demanding period of time for an animal), this should create an advantage for dark morph individuals. However, the morphs do not show a difference in survival rate or fecundity, only when they come together as a pair, in a mixed-morph (consisting of a light and dark morph individual) or a like-morph pair (consisting of only either light or dark morph individual), there is a difference: Mixed-morph pairs were found to produce more young that have higher survival rates than offspring of like-morph pairs. Adding to our understanding of the mechanism promoting polymorphism in the species, this PhD will include (1) a study on prey provisioning rates and its consistency over the day to see whether there is a difference between pairs breeding as mixed-morphs or like-morphs that would explain higher productivity of a mixed-morph pair and higher survival of their offspring. (2) An immunological approach to explore whether chicks of mixed-morph and like-morph pairs differed in their baseline health and immune response that would explain the higher survival of offspring of mixed-morph pairs. (3) An experimental study to test whether a prey’s reaction time differed depending on the morph of an attacking hawk and ambient light levels that could be explained by morph- and ambient-light depending crypsis and lastly (4) perform a Bayesian integrated population model to explain the stable high frequency of dark morph individuals in absence of morph dependent survival and fecundity rates.

Tuesday, October 17, 2017 - 13:00

NIVEN Library, John Day Building, Upper Campus, UCT