Using bird foraging height guilds and species to assess forest degradation by livestock production

Abstract

Livestock production systems are the predominant use of drylands and offer a potential opportunity for biodiversity conservation. However, there is little consensus on what indicator should be used to assess the ecological status of dry forests under long-term livestock grazing management. We aimed to understand bird foraging height guilds and species responses to forest conditions and grazing intensity. We identified three forest conditions (mature forests, successional forests, and open areas). Forest condition was the main factor influencing bird foraging height guilds. We found that the richness and abundance of bird foraging height guilds were drastically lower in open areas, while mature and successional forests showed higher values. Grazing intensity showed a positive association only with canopy-foraging bird abundance. Ground-foraging bird responses to grazing intensity depended on forest conditions, decreasing drastically their abundance as grazing intensity increased in open areas. Understory-foraging birds were the most responsive guild to forest conditions, with their richness and abundance increasing from open areas to successional forests, indicating their potential as ecological forest status monitors. In addition, species composition differed among forest conditions, with specific bird species associated with each condition. For example, Myiarchus swainsoni and Drymornis bridgesii were indicators of mature forests characterized by old-growth trees. In turn, Synallaxis frontalis, Saltator aurantirostris, Leptotila verreauxi, Cyanoloxia brissonii, Zonotrichia capensis, Hemitriccus argaritaceiventer, and Lepidocolaptes angustirostris were characteristic of successional forests characterized by shrub encroachment. Finally, Nothura maculosa, Anumbius annumbi, and Schoeniophylax phryganophilus were associated with open areas with high grass cover but with a few scattered trees. These bird species and guilds could be used as indicators of forest conditions, constituting a valuable tool to promote biodiversity conservation and management decisions.