The impact of cattle grazing regimes on tropical savanna bird assemblages

Abstract

Globally, agricultural land use is implicated in the decline of avifauna. In rangelands (areas used for livestock grazing), bird community responses to grazing can be complex, species-specific and scale dependent. A greater understanding of bird responses to grazing will lead to more meaningful management recommendations. We tested the hypothesis that foraging height predicts bird species' responses to grazing, such that species using lower vegetation strata are most likely to respond to the impacts of livestock grazing. We examined the response of a tropical savanna bird community to four grazing strategies at a long-term grazing trial in northern Australia. We predicted that ground-foraging guilds would be more responsive to grazing treatment than foliage-or aerialforaging guilds. We analysed the bird community assemblage using generalised linear mixed models and examined individual species' abundance in relation to microhabitat variables. We found that while ground-foraging guilds were more responsive to grazing treatment, individual species dynamics within a foraging guild could be contradictory. For example, the red-backed fairy-wren decreased in abundance with increased grazing and was positively associated with grass and shrub (Carissa ovata) cover, whereas Australian magpies increased in abundance in the most heavily grazed paddocks. In general, the responses of bird species to grazing were more pronounced in guilds that forage closer to the ground, but whether the responses were positive or negative was driven by bird species ecology. Measures examining the responses of individual species are more useful than assemblage measures (such as richness) to describe the impacts of anthropogenic disturbance such as grazing.

Occurrence patterns of the endangered Yellow Cardinal Gubernatrix cristata in north-east Argentina: only in savannahs and at sites away from roads

“…The effects of livestock grazing on bird assemblages are highly variable (Davies et al . 2010, Neilly and Schwarzkopf 2019), partly because the effects of grazing livestock on ecosystems vary with the type of herbivore (Sankaran et al 2008). Moreover, livestock grazing effects are difficult to assess due to scarcity of areas without livestock grazing (Bellis and Muriel 2015).…”

Peer Review #2 of "Grazer density and songbird counts in a restored conservation area (v0.1)"

“…Similar to our study, Köhler et al (2016) and Kerekes & Végvári (2016) found that associations between bird abundance and grazing intensity varies greatly among bird species. Also Neilly & Schwarzkopf (2019) described that responses of birds to grazing are often complex and will reflect habitat requirements of the individual bird species. Whether a possible effect of natural grazing in a nature reserve is meeting conservation goals thus depends on which species one aims to protect.…”

A global review identifies agriculture as the main threat to declining grassland birds

“…Conversion of grassland to forestry further threatens birds reliant on open anthropogenic habitat (Mortelliti & Lindenmayer 2015). Groundnesting species are particularly sensitive to high grazing pressure from livestock, whereas groundforagers are less sensitive (Baker-Gabb et al 2016, Neilly & Schwarzkopf 2019.…”

“…Many Australasian grasslands, including 95% of Australia's Northern Plains (Department of Sustainability and Environment 2010), have been lost or degraded by conversion for livestock pastures and cropping, impacting a range of grassland birds including the Plains‐wanderer Pedionomus torquatus (Baker‐Gabb et al . 2016, Neilly & Schwarzkopf 2019) and Golden‐shouldered Parrot Psephotellus chrysopterygius (Crowley & Garnett 1998). Conversion of grassland to forestry further threatens birds reliant on open anthropogenic habitat (Mortelliti & Lindenmayer 2015).…”