Conservation in a changing world: assessing the conservation status of an agruculturally adapted species, the Blue Crane. Chapter 2: Population Trends

<p dir="ltr">Data analysed for Chapter 2 in Craig CA. 2024. <a href="http://hdl.handle.net/11427/40848" rel="noreferrer" target="_blank">Conservation in a Changing World: Assessing the Conservation Status of an Agriculturally Adapted Species, the Blue Crane</a>. PhD. University of Cape Town.</p><p dir="ltr">Understanding the population demographics, distribution and habitat use of a species is key to its conservation. Using aerial survey, road count and ad-hoc sighting data, I detail the population estimates, flock demographics, distribution, and habitat use of Blue Crane <i>Anthropoides paradiseus</i>. I analyse citizen science data from the Coordinated Avifaunal Roadcounts (CAR) and Southern African Bird Atlas Projects (SABAP) to assess population trends across the Blue Crane range. I conducted winter and summer aerial surveys in the Western Cape wheatlands (Overberg and Swartland), using transects/distance sampling and one in winter 2021 in the Karoo. A quadrat design was used in the Karoo because Blue Crane distribution is patchier than the Western Cape. Using distance modelling, I estimate there to be 25458 (95% CI 21883–29618) Blue Cranes in the Overberg and 6072 (5211–7076) in the Swartland. In the Karoo, the total count was 9331, and a crude stratified extrapolation gave an estimate of 16464. Given the grassland population of some 4000 cranes, I estimate a population of 51000 (range 34000–68000) Blue Cranes in South Africa, which is double the last estimate from 2002. Across all CAR precincts, summer counts of Blue Cranes increased by 24% (95% CI 3.4–51%) between 2000 and 2019 and SABAP reporting rates increased by 6.3% between SABAP1 (1989–1994) and SABAP2 (2007–2022). However, in 2010, the CAR population trend changed from positive to negative; since 2011, summer counts have declined by 19% (95% CI –31 to –5.2%), driven primarily by Overberg numbers declining by 22% from 2011–2019 (–37 to –1.9%). Continued CAR counts will be important to ascertain whether the population has stabilised at a lower density or is continuing to decrease. In winter, Blue Cranes select for pastures (especially lucerne and lupin fields) in the Karoo and Western Cape wheatlands. Flock sizes were significantly larger in the Karoo than the Western Cape, with flocks up to 1200 counted on irrigated lucerne fields. In both areas there is occasional conflict between farmers and cranes, as cranes can trample lucerne, damage sweet lupins and be perceived as a nuisance at feedlots. Selecting for pastures is a potential ecological trap for the species, particularly if social factors lead to lowered tolerance among farmers. Coupling these risks with observed declines in the last 10 years, raises concerns about the status of the Blue Crane population.</p>