Response to urbanisation: aspects of the ecology of the Western Cattle Egret (Bubulcus ibis) with notes on population estimates in the KwaZulu-Natal province and across South Africa.

Abstract

Human population growth continues in Africa, impacting its natural fauna and flora. South Africa is experiencing a growth in population and metropolitan areas. KwaZulu-Natal is a province with the second fastest growing population in South Africa, with ~11.4 million people. This growing population is concentrated around Durban and Pietermaritzburg, the largest and second-largest cities in the province, respectively. This study focused on the city of Pietermaritzburg in the uMgungundlovu District Municipality, and Durban in the eThekwini Municipality, and their surrounding periurban areas, including communal lands and farmlands. As the response of Western Cattle Egrets (Bubulcus ibis) and selected heron species to urban expansion in KwaZuluNatal Province context is poorly documented, the purpose of this study was to understand aspects of the ecology of Western Cattle Egrets in these urban mosaic landscapes. Firstly, a literature review of the Western Cattle Egret was undertaken. Secondly, a comparison of the first Southern African Bird Atlas Project (SABAP1 conducted from 1987-1992) to the second Southern African Bird Atlas Project (SABAP2 ongoing since 2007) allowed us to observe range distribution changes of the Western Cattle Egret across South Africa. There was a significant difference for all changes observed in reporting rates between SABAP1 and SABAP2. With the exception of the Northern Cape, with a 22% decrease, provinces showed more than 60% decrease in reporting rates for the species between the two project periods. This indicated that there has been a decrease in Western Cattle Egret abundance nationally. Changes in reporting rates between SABAP1 and SABAP2 indicated a change in distribution range possibly caused by land transformation. Thirdly, population estimates of Western Cattle Egrets in the uMgungundlovu (Pietermaritzburg) and eThekwini (Durban) Municipalities, KwaZulu-Natal, South Africa, were i conducted over a period of 18 months. These areas are both urban mosaic landscapes with some remaining natural green areas as well as managed green spaces with urban built. A population estimate of Western Cattle Egrets was conducted within these districts, and characteristics that allow for their urban persistence were identified. No significant difference in population size existed between the breeding (~230) and the post-breeding (~470) seasons. Western Cattle Egret colonies were within 10 km of a landfill, wetland, major road, river, and grassland. In addition, nesting sites were closer to a wastewater treatment facility than roosts without nests. The nests were found on 27 trees in both commercial and residential properties. Vachellia xanthophloea and Jacaranda mimosifolia were used on commercial properties. A significant difference was observed for the mean tree height. The tallest trees used for roosting were Eucalyptus spp. (20.23 m) and Jacaranda mimosifolia (19.52 m) found at Mpophomeni. Western Cattle Egrets have become cosmopolitan, undertaking various forms of migration to exploit available resources in the urban landscape mosaic. The trends showed Western Cattle Egrets roost in urban mosaic landscapes near water. In some areas, human-egret conflict was observed. Management recommendations are made for the persistence of Western Cattle Egrets in urban mosaic landscapes.