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 kill. 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, now 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 research has focused on quantifying predation on tortoises and avian nest predation. Our current research builds on other research conducted at the Fitz, which suggested that crows may benefit from the road kills. We are exploring whether nesting densities or breeding demography differ depending on proximity to roads of different types (tar or gravel) and their associated road kills. Other research aims to improve our basic ecological understanding of the species.
Our research is currently focussed in the Hantam Karoo (Succulent Karoo). Within our 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 breeding crows that nest nearby. Additionally, we are seeking to understand the species’ home ranges and ranging behaviours both inside and outside of breeding seasons by using GPS tracking devices.
Activities in 2017
- Rona van der Merwe started her MSc dissertation on Pied Crow ecology in the Karoo.
- Rona monitored 14 nests (six on gravel roads, eight on tar roads), and documented road kills from over 2 000 km of road transects.
- Two active nests had 41 tortoise carapaces on the ground below the nests. Rona set up a camera trap at one of these nests, which revealed that Pied Crows do not take tortoises to the nest, but rather prepare them nearby and take the meat to the nestlings. This is important because it means that checking of the areas around nests for tortoise remains might significantly under-estimate the numbers of small tortoises killed by Pied Crows.
- Carles Durà completed his CB MSc project entitled “Understanding predation of tortoises by nesting Pied Crows (Corvus albus) in western South Africa”. The thesis is currently being prepared for publication.
- Rona successfully captured one Pied Crow and fitted a GPS tracker to the bird – this is the first Pied Crow to ever be tracked.
- A 2015 review paper on the impact of corvids on other bird species by CB MSc student Chrissie Madden and Arjun Amar was the most highly cited paper from the journal Ibis in 2017.
- Research associates Grant Joseph and Colleen Seymour had an article published in early 2017 on the influence of road kill in explaining Pied Crow population increases (Joseph et al. 2017. Biological Conservation).
Impact of the project
This research aims to build our understanding of whether the increase in Pied Crows in certain regions of South Africa represents a 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 Susie Cunningham (FIAO, UCT)
Dr Robert Thomson (FIAO, UCT)
Dr Thomas Flower (FIAO, UCT and Simon Fraser University)
Dr Grant Joseph (FIAO, UCT and University of Venda)
Dr Colleen Seymour (FIAO, UCT and SANBI)
Students: Rona van der Merwe (MSc, UCT); Carles Durà (CB MSc, UCT).