Habitat transformation and climate change: Implications for the distribution, population status, and colony extinction of Southern Bald Ibis (Geronticus calvus) in southern Africa

Abstract

Habitat transformation and loss is one of the greatest threats currently facing avian species. The cumulative impact of climate change on habitat loss is projected to produce disproportionate risk for endemic high-altitude species. The Southern Bald Ibis (Geronticus calvus) is an endemic high-altitude species found throughout highland grassland habitats in South Africa and Lesotho. The historical distribution has contracted notably and causal factors remain ambiguous. Furthermore, the historical population (1950–1970) was believed to be stable, but recent local surveys suggest colony declines and the current global population status remains largely unquantified. We assessed the current distribution and population status of the species through predictive modeling and trends in historical and recent colony counts across the species’ range. We examined climate and habitat change as potential causal factors contributing to the historical contraction in distribution, and projected the potential impact of future climate change predicted by global circulation models. Our study confirms that Southern Bald Ibis are of conservation concern. The loss of grasslands to expanding woody vegetation through bush encroachment was the most detrimental habitat transformation type associated with decreased colony growth and colony collapse. We recommend maintaining a minimum threshold of 50% or greater intact grassland habitat surrounding colonies to reduce colony extinction risk and promote colony persistence.

Modeling Future Potential Distribution of Buff-Bellied Hummingbird (Amazilia yucatanensis) Under Climate Change: Species vs. Subspecies

“…Future geographical distribution might be related to the tolerance to a wide range of climatic conditions that facilitates the occupation of large geographic areas (Atauchi et al, 2020;Freeman et al, 2019;Slatyer et al, 2013). Although range-restricted species are predicted to be more vulnerable to global warming (Colyn et al, 2020;Urban, 2015), our results showed that the effects of climate change are not restricted to rangerestricted or habitat specialist species (Dirnb€ ock et al, 2011;Malcolm et al, 2006), and depends on multiple factors, as shown for A. y. yucatanensis and A. y. chalconota. In this study, the subspecies with strong cinnamon coloration (A. y. yucatanensis) showed the highest increase in future distribution area, while the predicted area for the subspecies with less cinnamon coloration (A. y. chalconota) decreased in all future climate-change scenarios.…”

“…Several studies have evaluated the effects to climate change on current distribution of bird species and showed that the potential distributions in some species is reduced (Atauchi et al, 2020; Knudsen et al, 2011), expand northwards (Hitch & Leberg, 2007; Lara et al, 2012), shifted and contracted when exacerbated by habitat loss (Colyn et al, 2020), and in some cases the impacts of climate change on current distributions of birds were minimal, particularly in range-restricted species (Freeman et al, 2019; Lara et al, 2012). Hummingbirds, as pollinators, are often immersed in highly dependent interactions with plants (Correa-Lima et al, 2019; Ornelas et al, 2004), and constitute the most diverse ensemble of specialized nectarivorous birds in the Americas (Sonne et al, 2016; Zanata et al, 2017).…”

An improved conservation status of Southern Bald Ibis Geronticus calvus as informed by a diversity of citizen science projects suggests positive impacts of conservation attention

“…hunting is not permitted. In this manuscript we do not consider ne scale spatial modelling as conducted by Colyn et al (2020). In that study, declines in areas of occupancy (AOO) are evident due to encroachment by invasive alien vegetation and loss of grassland habitat.…”

“…The Southern Bald Ibis Geronticus calvus is a cliff-nesting species of the Threskiornithidae family, with a range restricted to the grassland biome of South Africa, Lesotho and Eswatini (Henderson 2015). This species favours high-altitude mesic grasslands and agricultural lands with high rainfall and rugged terrain, without the encroachment of trees, shrubs, and bushes (Henderson 2015;Colyn et al 2020).…”

“…Historical population estimates suggested a total breeding population of 2000 (Siegfried 1971) to 4000 (Manry 1985a) birds. More recent population estimates suggest a total breeding population of approximately 3000 birds (Henderson 2015;Colyn et al 2020). These estimates were derived from colony surveys, which further postulated that only 48.5% of the birds present at colonies during the breeding season were breeding individuals (Colyn et al 2020).…”