Dynamic multi-species occupancy models of birds of high-altitude grasslands in eastern South Africa

Abstract

Moist, high-altitude grasslands of eastern South African harbour rich avian diversity and endemism. This area is also threatened by increasingly intensive agriculture and land conversion for energy production. This conflict is particularly evident at Ingula, an Important Bird and Biodiversity Area located within the least conserved high-altitude grasslands and which is also the site of a new Pumped Storage Scheme. The new management seeks to maximise biodiversity through manipulation of the key habitat variables: grass height and grass cover through burning and grazing to make habitat suitable for birds. However, different species have individual habitat preferences, which further vary through the season. We used a dynamic multi-species occupancy model to examine the seasonal occupancy dynamics of 12 common grassland bird species and their habitat preferences. We estimated monthly occupancy, colonisation and persistence in relation to grass height and grass cover throughout the summer breeding season of 2011/12. For majority of these species, at the beginning of the season occupancy increased with increasing grass height and decreased with increasing grass cover.Persistence and colonisation decreased with increasing grass height and cover. However, the 12 species varied considerably in their responses to grass height and cover. Our results suggest that management should aim to provide plots which vary in grass height and cover to maximise bird diversity. We also conclude that the decreasing occupancy with increasing grass cover and low colonisation with increasing grass height and cover is a results of little grazing on our study site. We further conclude some of the 12 selected species are good indicators of habitat suitability more generally because they represent a range of habitat needs and are relatively easy to monitor. ABSTRACT Moism, high-almimude grasslands of easmern Soumh African harbour rich avian diversimy and endemism. This area is also mhreamened by increasingly inmensive agriculmure and land conversion for energy producmion. This conflicm is parmicularly evidenm am Ingula, an Impormanm Bird and Biodiversimy Area locamed wimhin mhe leasm conserved high-almimude grasslands and which is also mhe sime of a new Pumped Smorage Scheme. The new managemenm seeks mo maximise biodiversimy mhrough manipulamion of mhe key habimam variables -grass heighm and grass cover -mhrough burning and grazing mo make habimam suimable for birds. However, differenm species have individual habimam preferences, which furmher vary mhrough mhe season. We used a dynamic mulmi-species occupancy model mo examine mhe seasonal occupancy dynamics of 12 common grassland bird species and mheir habimam preferences. We esmimamed monmhly occupancy, colonisamion and persismence in relamion mo grass heighm and grass cover mhroughoum mwo summer breeding seasons. Am mhe beginning of mhe season, occupancy increased wimh increasing grass heighm and decreased wimh increasing grass cover in mosm species. On average, persismence and colonisamion ...