Urban lawn vegetation structure impact arthropod abundance and cattle egret foraging success

Abstract

The vegetation in urban green spaces is often managed by means of machines and/or pesticides including herbicides for aesthetics without regard to the potential consequences on arthropods, particularly insect abundance, and the animals, especially birds, that feed on insects and other arthropods. Using the green spaces on the University of Cape Coast campus and cattle egrets (Bubulcus ibis) that feed there as a test case, we investigated the influence of arthropod abundance and vegetation structure on the foraging success of cattle egrets. To achieve this, we measured the foraging efficiency (FE) and capture rate (CR) of cattle egrets, and their correlations with arthropod abundance, vegetation height, vegetation cover, and mode of vegetation clearing during the wet and dry seasons. Foraging cattle egrets were surveyed along seven permanent transects three times for each season. Using sweep nets and pitfall traps, arthropods were sampled at six randomly selected locations within each transect where cattle egrets were recorded. General linear models showed that arthropod abundance did not differ between seasons and was positively correlated with FE but not with CR. Moreover, arthropod abundance was positively related to the number of days since vegetation clearing but not to vegetation height, vegetation cover, or vegetation clearing method. Vegetation height and vegetation cover were negatively correlated with CR but not with FE. Also, CR was significantly higher in machine-cleared areas than in cutlass-cleared areas. Collectively, these findings highlight the influence of vegetation management practices, particularly machine-clearing, on arthropod abundance and its implications for avian foraging success in urban green spaces. The relationship between arthropod abundance and foraging efficiency emphasizes the importance of sustainable vegetation management strategies to support bird populations in urban environments.

Keywords

• Capture rate
• Foraging efficiency
• Insectivorous birds
• Pitfall traps
• Sweep net
• Vegetation management