An update on the conservation status of the Little Bustard Tetrax tetrax: global and local population estimates, trends, and threats

Summary The Little Bustard Tetrax tetrax is an iconic species and an indicator of healthy grassland and farmland ecosystems. It formerly ranged almost continuously from north-western Africa and Iberia to central Asia, encompassing France, Italy, southern Russia, and the Middle East, occupying natural grass steppes, pastured grasslands, and extensive cereal farmland. Today, two main distribution sub-ranges persist: a western one comprising the Iberian Peninsula, France, and Sardinia, and an eastern one encompassing mainly southern Russia and Kazakhstan but reaching north-western China and isolated spots in Turkey. We describe the changes that occurred across the species’ range and were documented during the last and current centuries and revise the status and trends of Little Bustard populations throughout that range. We provide the first global estimate of the world population, as well as those of the two sub-ranges, discussing the main threats and global conservation implications of these estimates. Historically abundant in Europe and northern Africa, the Little Bustard has strongly declined over the second half of the 20th century, becoming extinct in at least 15 countries. Such spectacular regression is mainly associated with land-use change and agricultural intensification. Other threats are legal hunting, poaching, and collision with powerlines. In the last two decades, the species has severely declined (c.6% yearly rate) in its traditional population stronghold, the Iberian Peninsula. Conversely, there is evidence of recent population growth in some areas of the Eastern range, but increases are unquantified and require further study. Many populations are probably small and scattered, with no reliable information on size and trends. Nevertheless, the Eastern range may now be considered the species’ stronghold with more than half the world’s population. The diverging dynamics and ecological differences between the two sub-ranges require a global conservation strategy that treats each as a different conservation unit to assure the species’ recovery.

Taxonomic and ecological composition of the native groupings of the birds of the dry steppe zone of Ukraine

The classifications of the grouping of the birds reflect the faunistic or the ecological position of the species in certain habitats and landscapes. Most of them consider the species diversity of the birds of the studied regions in general, including synanthropic, invasive and widespread species. This approach prevents singling out the habitats which are important for supporting the existence of native (or autochtonous) species and their groupings. Native groupings of the birds in the dry steppe zone of Ukraine are almost not studied despite the rapid contraction in the range and population of most component species, especially Anthropoides virgo, Otis tarda, Tetrax tetrax and Burhinus oedicnemus. The definition of the taxonomic and the ecological composition of these grouping will help in understanding the strategy of the reproduction and the protection of native avifauna. In connection with this, the faunistic-topomorphic classification of native birds in the dry steppes zone of Ukraine according to the following scheme is proposed: ornithofaunistic complex (by priority landscapes and habitats) – the place of the feeding (by priority substrate on/in which a species’ diet is extracted) – the nesting place (by the priority substrate of the location of the nest for nesting individuals) – the place of rest (the priority substrate where non-nesting individuals rest). The classification is aimed at the definition of the general requirements of native birds and their groupings in terms of the landscapes and the habitats which provide the conditions for their preservation and the protection in the researched region. It has been determined that in the south of Ukraine 33 nesting species are dry-steppe autochthons (18.3% of nesting species of the region), of which 18 species form the ornithofaunistic complex of dry steppes (Buteo rufinus, Perdix perdix, Anthropoides virgo, Otis tarda, Tetrax tetrax, Burhinus oedicnemus, Glareola nordmanni, Galerida cristata, Calandrella cinerea, C. rufescens, Melanocorypha calandra, Anthus campestris, Motacilla feldegg, Saxicola rubetra, S. torquata, Oenanthe oenanthe, Oe. isabellina, Emberiza melanocephala), and 15 species form the complex of the sea coast (Phalacrocoraх aristotelis, Phoenicopterus roseus, Tadorna ferruginea, T. tadorna, Mergus serrator, Charadrius alexandrinus, Recurvirostra avosetta, Larus ichthyaetus, L. melanocephalus, L. genei, L. cachinnans, L. michahellis, Gelochelidon nilotica, Hydroprogne caspia, Thalasseus sandvicensis). The above-mentioned species are mainly xerophiles (54.6% of species) and hygrophils (24.2% of species), and they are in the most threatened position because they feed, nest and rest mainly or exclusively on the soil surface. According to the proposed classification, native birds of dry steppes require: for xerophiles – areas of soil without vegetation or with rarefied low grass, which does not prevent birds from moving freely, searching and obtaining food, leading their chicks, looking over their territories; for hygrophiles – shallow water bodies with islands, surface vegetation, shallows, adjacent meadows and salt-marshes; for dendrophiles – single shrubs and trees or small groves; for most xerophiles and dendrophiles – fresh or slightly saline water bodies for drinking. Unfortunately, in the protected natural territories of the researched region, most native birds do not have this combination of the above-mentioned habitats, which are simultaneously suitable for feeding, nesting and resting.

Little Bustard (Tetrax tetrax Linnaeus, 1758) Number Observation on the Rostov Nature Reserve Grounds the Middle of 20th Century to 2020

The purpose of the work. Elucidation of changes in the number and distribution of little bustard (Tetrax tetrax Linnaeus, 1758) on the territory of the Rostov Nature Reserve in the 20th-21st centuries and the reasons for their transformation. Place and methods of work. The reserve is located in the arid Eastern European steppes. The authors used their own observations from 1959 and publications on Tetrax tetrax L. The materials are collected using regular route methods and animal tracking at individual sites, as well as analysis of published information. Results. The little bustard is a characteristic steppe species that historically lived on the Don land. Since the mid-twentieth century, the steppes have experienced deep anthropogenic changes, which have had a great impact on this species. Currently, the little bustard in the steppe zone is a rare species. The creation of the reserve has had a positive impact on this species. In it, the little bustard is a small breeding species, and its number is constrained by a number of factors. The intensification of economic activity in the region and the aridization of the climate make it necessary to improve environmental protection work.

Changes in grassland management and linear infrastructures associated to the decline of an endangered bird population

European grassland birds are experiencing major population declines, mainly due to changes in farmland management. We analyzed the role of habitat availability, grazing management and linear infrastructures (roads and power lines) in explaining spatial and temporal variation in the population density of little bustards (Tetrax tetrax) in Portugal, during a decade in which the species population size halved. We used data from 51 areas (totaling ca. 1,50,000 ha) that were sampled in two different periods (2003–2006 and 2016). In 2003–2006, when the species occurred at high densities, habitat availability was the only factor affecting spatial variation in bustard density. In the 2016 survey, variation in density was explained by habitat availability and livestock management, with reduced bird numbers in areas with higher proportions of cattle. Population declines across the study period were steeper in areas that initially held higher densities of bustards and in areas with a higher proportion of cattle in the total stocking rate. Areas with higher densities of power lines also registered greater density declines, probably due to avoidance behavior and to increased mortality. Overall, our results show little bustards are currently lacking high quality grassland habitat, whose persistence depends on extensive grazing regimes and low linear infrastructure densities.

Power line routing and configuration as major drivers of collision risk in two bustard species

Collision with power lines is a major cause of mortality for many bird species. Understanding the biotic and abiotic factors that increase collision risk is therefore important for implementing mitigation measures to minimize mortality, such as power line rerouting or wire marking. Here, we used collision events registered during 2003–2015 along 280 km of transmission power lines in southern Portugal to analyse spatio-temporal patterns and collision risk factors in two sympatric, threatened, and collision-prone species: the great bustard Otis tarda and the little bustard Tetrax tetrax. The occurrence of collisions was not uniform across space and time, and variations could be explained by the species' ecological requirements, distribution patterns and behaviour. Although both species fly considerable distances between areas of suitable habitat, collisions were far more likely in power line sections with > 20% (for the little bustard) or > 50% (for the great bustard) of open farmland habitat in the surroundings. Power line configuration was also important: taller pylons and those with a higher number of wire levels posed a higher risk for both species. Wire marking had a small but significant effect for the little bustard, reducing collisions risk. There was, however, no similar effect for the great bustard, possibly a result of limited data. Mitigation measures should be implemented to prevent bustard collisions, including adequate route planning, ideally avoiding areas with > 20% of open habitat. Line configuration and wire marking are particularly important where such localities cannot be avoided and power lines cross areas with a high proportion of bustard habitat, including outside protected areas.