Surveys of wintering Little Bustards Tetrax tetrax in central Spain: distribution and population estimates at a regional scale

Abstract

SummaryDeveloping a standardized survey methodology to census and estimate the size of wintering populations is a main conservation priority for the endangered Little Bustard. We present a standard and repeatable methodology to census wintering Little Bustard populations at a regional scale, and the first statistically reliable population estimate of a Little Bustard wintering population in Spain. We carried out two surveys, in 2003 and 2004, using UTM 10 km 6 10 km squares as census units, which were subjected to stratified sampling over the species' potential distribution range in the region of Madrid (Central Spain). Only the areas of potentially suitable habitat within squares of known winter presence of the species were considered. The species' winter distribution in Madrid was fairly constant between years, showing a fragmented pattern in three main nuclei. The number of Little Bustards observed was consistent between surveys (752 and 786 birds, respectively), with birds grouped in an average of 32 flocks (1 to 350 birds, mean 5 27.9 birds). No between-winter differences in flock size were observed, although differences between sectors were significant. The highest densities were observed in the Tagus valley (mean density 5 2.9 birds km 22 , 293 birds), followed by north-eastern farmland (mean density 5 0.6 bird km 22 , 269 birds). The estimated size of the Little Bustard population wintering in the Madrid region was 1,051 (95% CI 5 1,043-1,231). This calculation was based on recorded population density, measured as the number of birds per square kilometre, and considers the potential habitats available in each sector. We propose this methodology as adequate for surveying any Little Bustard wintering area, at both regional and smaller spatial scales. Survey results are consistent with previous tentative estimates for the region of Madrid, and with available information on Little Bustard movements. Sixty-five per cent of squares with Little Bustard presence were outside any protected area, which makes the wintering Little Bustard population of Madrid highly vulnerable to habitat disappearance and may affect the viability of breeding nuclei whose individuals winter in the region.

Diet composition of a declining steppe bird the Little Bustard (Tetrax tetrax) in relation to farming practices

“…1; García de la Morena et al 2007, Ponjoan et al 2012, Tarjuelo et al 2013. Irrigated farmlands were covered by a large variety of crops, although dominated by winter-sown cereal and maize crops, as well as alfalfa fields and fruit-tree orchards (Table 1).…”

Migration of wild and captive‐bred Little BustardsTetrax tetrax: releasing birds from Spain threatens attempts to conserve declining French populations

“…(1996). The survey in our study covered the wintering areas where French PTT‐fitted birds had been recorded in previous years and sites where Bustards were known to overwinter (García de la Morena et al. 2002, 2007).…”

“…The procedures used for scanning the frequencies and manoeuvring the aircraft to locate the transmitters followed those detailed in Kenward (2001) with adaptations proposed by Gilmer et al (1981) and Alonso et al (1996). The survey in our study covered the wintering areas where French PTT-fitted birds had been recorded in previous years and sites where Bustards were known to overwinter (García de la Morena et al , 2007.…”

“…Once continuously distributed from Iberia to Russia, this species experienced a drastic decline in its range during the 20th century (Cramp & Perrins 1994), and Western European populations ( T. tetrax ) are now restricted to Portugal, Spain, France and Italy, with an estimated 110 000–280 000 individuals, primarily in Iberia (Birdlife International 2000). Numbers are currently declining in all these countries (García de la Morena et al. 2006, 2007, Jolivet & Bretagnolle 2002, Cabral et al.…”

Distance to international border shapes the distribution pattern of the growing Little BustardTetrax tetraxwinter population in Northern Iran

“…Agricultural intensification, habitat loss and degradation across the species’ geographical range are thought to be the main factors depleting its populations (e.g. Silva et al 2004, García de la Morena et al 2007, Suárez-Seoane et al 2008, De Juana 2009, Delgado et al 2009, Iñigo and Borov 2010).…”