Summary
The South African Fynbos biome, a global biodiversity hotspot with high endemism and species rich ness, has six endemic bird species. These are important not only intrinsically, but also for ecological functioning and as flagships for South Africa’s economically valuable avitourism sector. Little is known about population sizes or realised distribution ranges of these six species, but projected range model ling based on occurrence from the South African Bird Atlas Project (SABAP) has suggested these species are vulnerable to climate change. We estimate global population sizes for these six endemics based on densities calculated from two intensive biome-wide point count surveys in 2012. We modelled regions of suitable climatic space, from which we established that mean annual tempera ture and the temperature of the warmest quarter of the year appear to limit Cape Rock-jumper Chaetops frenatus and Protea Canary Serinus leucopterus ranges. Both species have seen an appar ent > 30% decrease in range and reporting rates (a proxy for abundance) in the twenty years between SABAP atlas periods (1987–1991 and 2007–ongoing). The Cape Rock-jumper result is unexpected: encounter rates are higher in shorter vegetation, dry slopes and habitats with more recent occurrence of fire – all proxies for proximate causes of climate change on the Fynbos. Although coastal plains are highly transformed, mountain Fynbos is the best protected of all the world’s Mediterranean-climate habitats, with relatively little anthropogenic land transformation. Long term weather datasets from the Fynbos demonstrate significant warming since 1960. We conclude from these lines of evidence that these decreases are consistent with the loss of suitable climate space and inability of these species to adjust physiologically to increasing temperatures.
Introduction
The Fynbos region at the south-western tip of Africa is one of five Mediterranean-type biomes of the world. All five are considered global conservation priority areas owing to high plant species diversity and density, as they cover just 2% of the Earth but account for 20% of the Earth’s vas cular plant species (Cowling et al. 1996 , Myers et al. 2000 , Olson and Dinerstein 2002 ). By 2100, the Mediterranean biomes are projected to experience the largest proportional loss of biodiversity of all terrestrial biomes due to their significant sensitivity to multiple biodiversity threats and interactions among these threats (Sala et al. 2000 ). For example, the biomes’ mild climate and proximity to the ocean makes them attractive to humans, resulting in disproportionately high conversion for agriculture, development, and other human uses. In addition, extensive global cli mate change modelling on the impacts on avian biodiversity suggests that the south-western corner of South Africa is an area at risk (Foden et al. 2013 ). Furthermore, modelling exercises of all the five Mediterranean-climate habitats suggests the Fynbos is one of the two facing greatest potential changes in climate (Klausmeyer and Shaw 2009).
Species that are both highly climate change vulnerable and threatened, as well as the regions in which they are concentrated, deserve particular conservation attention to mitigate current threats and to plan for future climate change adaptation interventions. Africa (excluding the Sahara and Congo basin) has been identified as one of these regions (Foden et al. 2013 ). Several African bird species have been identified as being potentially vulnerable to climate change due to restriction to upper-montane areas or other life-history traits (Monadjem et al. 2013 , Simmons et al. 2004 ). To date there have been few studies that have validated these predictions from Africa.
Climate in the Fynbos is predicted to get drier and hotter (Klausmeyer and Shaw 2009 ) and is already experiencing an increase in extreme weather events (Kruger and Sekele 2013 ). While fires are an important natural disturbance essential to the life-history strategies of many Fynbos plant species, there are also indications from several sources that climate changes are resulting in detri
mental increases in fire frequency (Kraaij et al. 2012 , Southey 2009 , Wilson et al. 2010 ). Previous studies of the probable impacts of climatic change on plants of the Fynbos biome have highlighted a likely reduction in biome extent, species’ range displacements and potential extinctions (Midgley et al. 2002 ). Huntley and Barnard ( 2012 ) projected similar outcomes for birds associated with the Fynbos and grassland biomes in southern Africa. Du Plessis et al. ( 2012 ) and Cunningham et al.
( 2013 ) have also shown that in arid environments of South Africa, increasing temperatures have repercussions for behaviour, foraging success, body mass maintenance, and ultimately reproduc tive output for at least two bird species.
The Fynbos is an important habitat type in terms of avian species richness for South Africa. It supports six endemic passerine bird species (Barnes 1998 , BirdLife International 2013 ) and a fur ther six of South Africa’s 18 endemics are frequently encountered here (Lee unpubl. data). The avian community of mature mountain Fynbos is dominated by the endemic nectarivores Cape Sugarbird Promerops cafer and Orange-breasted Sunbird Nectarinia violacea (Siegfried and Crowe 1983 ). Insectivorous Victorin’s Scrub-warbler Bradypterus victorini is associated with rank vegetation of mesic mountain Fynbos (Fraser 1997a ), while Cape Rock-jumper Chaetops frenatus prefers open, rocky habitats associated with ridges or mountain tops (Maclean 1993 ). Granivorous Cape Siskin Crithagra totta occurs in habitats dominated by Restios (Fraser 1997b ), while Protea Canary Serinus leucopterus is associated with open, often arid, Fynbos with a dis persed canopy of tall Protea (Milewski 1976 ). We aim to provide information that will inform decision-making processes regarding the conservation status of these species, with special reference to the vulnerability of some of them to climate change. To do so we calculate population sizes, global ranges, and examine population trends from bird atlas data. Climate change may influence species’ distributions directly, through species’ intolerance for temperature extremes, or indirectly through modifications of habitat (specifically vegetation) by temperature, rainfall and vulnerability to fire. We predict species will differ in their responses to climate-related influences on vegetation, but that all will display thermal intolerance for warm temperatures as this is a trend observed for high-elevation bird species (Sekercioglu et al. 2008 ), and Fynbos biota evolved under mainly cooler conditions (Midgley et al. 2005 ).