Understanding the ecological impacts of Pied Crows
Pied Crow Corvus albus numbers are increasing in many parts of South Africa. Recent work at the Fitz suggests that the increase in Pied Crow numbers is a result of global warming and other anthropogenic factors including the availability of nest sites on electrical infrastructure and increased food availability in urban areas and from road kills. In combination, these factors have seen the Pied Crow increase its abundance in some regions and expand its range locally. Our project investigates the expansion of this species, sometimes termed a ‘native invader’ species, and tries to understand what impacts these changes might have for other biodiversity.
As a generalist predator, Pied Crows may impose heavy predation pressure on a variety of prey species. Anecdotal evidence suggests that Pied Crows present a risk to threatened species, such as endangered breeding waders and range- restricted tortoises. Recently, researchers and conservation organisations have begun drawing attention to the knowledge gap with regards to the ecological impacts of Pied Crows, emphasizing the need for more studies. Indeed, there is little information about the basic life history of Pied Crows, which is an essential component for understanding the potential impacts of a predator. We aim to contribute to filling these knowledge gaps. Previous Fitz research has focused on quantifying predation on tortoises and avian nest predation. Our current research builds on that research, which suggested that crows may benefit from scavenging on the carcasses of road kills. To test this idea, we are exploring whether nesting densities or breeding demography differ depending on proximity to roads of different types (tar or gravel) and their associated levels of road kills.
Our research is focussed in the Hantam Karoo (Succulent Karoo), where crow densities are known to have increased substantially. Withinour study area we have crows nesting adjacent to tar roads and to gravel roads and we are examining the numbers of road kills found on these different roads, as well as monitoring the abundance and breeding performance of the crows which nest by these different road types.
Activities in 2018
- Rona van der Merwe continued collecting data (breeding data and road kill records) for her MSc dissertation.
- None of the 15 crow nests monitored in 2018 showed any evidence of tortoise predation by breeding pairs.
- GPS tagging of Pied Crows to determine home ranges was suspended in 2018 after trapping crows proved to be more challenging than expected.
- Rona has documented road kills from >4000 km of road transects and found that, as expected, road kills were higher on tar thangravel roads.
- Rona monitored 29 Pied Crow nests along gravel and tar roads from 2017– 2018, which will allow breeding performance to be compared between these two road types.
Impact of the project
This research aims to build on our understanding of drivers of increasing Pied Crow abundances in certain regions of South Africa and determine the associated conservation problem, and if so, what management actions might be most effective to deal with these concerns.
DST-NRF CoE grant, Francois van der Merwe.
Dr Arjun Amar (FIAO, UCT)
Dr Robert Thomson (FIAO, UCT)
Students: Rona van der Merwe (MSc, UCT) .