Bustard Population Research Articles

Temporal trends of land-use favourability for the strongly declining little bustard: assessing the role of protected areas.

The little bustard (Tetrax tetrax) is a steppe bird strongly and negatively influenced by agricultural intensification in Europe. Here, we use the little bustard as a model species to examine how favourability (relative occurrence likelihood of a species based on environmental characteristics, such as habitat availability) varies regionally with degree of protection in north-western Spain. The Natura2000 network is one of the main biodiversity conservation tools of the European Union, aiming to protect areas hosting species of conservation concern from unfavourable land-use changes. The network covers many landscapes across the continent, including farmland. Additionally, we examine the relationship between trends in land-use favourability and little bustard population trends over a decade in the Nature Reserve of Lagunas de Villafáfila, a protected area also in the Natura2000 network where active and intense management focused on steppe bird conservation is carried out. Favourability was much greater in Villafáfila than in both protected areas with lower degree of protection and in non-protected areas. Land-use favourability increased slightly between 2011 and 2020 both in and out of protected areas, whereas little bustard populations declined sharply in that period, even in Villafáfila. Spatial variations in little bustard abundance within Villafáfila depended on social attraction (increasing with the number of neighbouring males) but not significantly on small-scale variations in land-use favourability. These results suggest that land-use management in Natura2000 areas needs to be more conservation-focused, favouring natural and seminatural habitats and traditional farming practices to improve land-use favourability for little bustards and other steppe birds. Additional factors, such as field-level agricultural management or social interaction variables that may cause an Allee effect, should be incorporated in little bustard favourability models to improve their use in conservation planning.

Abundance and demographic structure of the great bustard (<i>Otis tarda</i>) (Otididae, Aves) population at lek areas in the Saratov and Volgograd Trans-Volga region

The results of our studies of the great bustard population in the Saratov and Volgograd Trans-Volga region are presented. For the first time in this territory, censuses of the numbers of bustards were carried out in their lek areas in the spring for 3 years. This made it possible to obtain more reliable data on the numbers of individuals of this species, as well as on the demographic structure in the model area and compare them with those obtained during autumn population counts. In our opinion, as a result of agriculture intensification, the nesting habitats of the bustard have been sharply reduced, which was caused by changes in the structure of crop areas and the massive use of pesticides. In the absence of necessary protection measures, this has led to a reduction in the numbers of birds in the Saratov Trans-Volga region by almost 10 times over 20 years. This trend is observed throughout almost the entire world range of the great bustard, where there are no long-term effective measures aimed at preserving the natural habitats of the species. In the Trans-Volga region, the number of lek areas has decreased by approx. half and the numbers of individuals of the species in the remaining leks have decreased. The demographic structure of the bustard population when studied in lek areas shows a significant predominance of males over females, which contradicts the stability of the population. Due to the reduction in the number of habitats suitable for bustards to nest, the success of their reproduction has significantly decreased. Spring treatment of crop areas with pesticides by ground and aerial methods coincides with the nesting period of birds, which is a powerful factor of disturbance and leads to the loss of clutches. Females whose clutches have been preserved, have the problem of acute food shortage after their chicks hatched, which also leads to elimination of some part of the broods.

Modelling the effectivity of a land sparing strategy to preserve an endangered steppe-land bird population in cereal farmland: Scopes and limits

Agricultural intensification and the disappearance of fallow land have been identified as a major driver of biodiversity loss in European farmland. In particular, the dramatic population decline of the little bustard (Tetrax tetrax), a flagship bird species in western European cereal farmland, has been largely attributed to the loss of this crucial habitat. Demographic modelling showed that low breeding success and reduced female survival were co-responsible for the little bustard population decline in a NE Iberian cereal pseudo-steppe. An equilibrium finite rate of change can be achieved by raising either female adult survival or fecundity. In both cases, the required increases fall within a biological meaningful range, but a combination of both would be more feasible in practice. Setting farmland aside as managed fallow can boost fecundity to the required equilibrium value, but the potential of this management action is seriously reduced as mortality increases. Socio-economically acceptable amounts of spared-land can only be achieved if actions to reduce mortality are undertaken in combination with providing fallow land. Actions to reduce both natural and anthropogenic mortality have so far been neglected by little bustard conservation programs. Both are needed if we seek to guarantee the long-term viability of the species and an acceptable share of conservation effort from stakeholders. Our results show that the holistic adaptive management approach adopted here can be used to evaluate the effectiveness and limitations of conservation decisions and to provide insights for conservation projects.

A túzok (Otis tarda L.) ízeltlábú táplálékforrás kínálatának vizsgálata alföldi előfordulási területein

We have carried out the tests in the four lowland regions where the Great Bustards are found: (1) Apajpuszta – Csepeli-plain (1985), (2) Mezőnagymihály – Borsodi Mezőség (1991), (3) Nagyiván – Hortobágy (1988) and Dévaványa – Dévaványai-plain (1985, 1987) (Map 1). We have collected the Arthropods in the study areas with BARBER pitfalls. Each of the annually selected habitats had 5 pitfalls in operation, which we have placed along a line at five meters from each other. The traps were in operation from May to July, sometimes until August. We emptied them in two-week (14-14 day) periods. During laboratory processing, we have determined the number of individuals and measured the total mass of individuals of each taxon per period. The individual and mass data were recorded in tables for each measurement (=every two-week period) and the dominance relationships were calculated, then the basic data were used to calculate the various community-ecological indicators (diversity, evenness, etc.). In addition to the calculated individual and mass ratios, we have also calculated the energy value and dominance of the samples. We have applied cluster analysis to group the animal food sources of each habitat. We have used the BRAY-CURTIS index as a similarity index. Based on the results obtained – regardless of the place and time of the examination – if we want to generalize, then we can say the following facts: (1) The mass and energy ratios that most characterize the food source prove that agricultural habitats are more favourable. (2) The food supply of the habitats changes during the reproduction period, partly for biological (seasonal dynamics of the taxa), partly for reasons of cultivation (mowing, harvesting) and with the maturation of the plants (disappearance of green phytomass), shows fluctuations, decreases or increases. The decrease is typical for cereals and natural grasslands, and the cyclical change is typical for mowed grasslands and alfalfa. We have experienced an increase in spring-sown (e.g. maize) habitats. (3) We cannot generally talk about the goodness of food sources within the same year, we must determine and prioritize the food supply in each period. (4) The extent and quality of the supply of Arthropod food sources is also different in the topographically different places of the Great Hungarian Plain. (5) It can be concluded that, based on the trappings, the decisive role of those taxa in the food supply of Arthropods can be demonstrated, which also play a decisive role in the animal food spectrum of the Great Bustards, so above all the Coleoptera and the Orthoptera. (6) Taking all of this into consideration, we should establish that regardless of the year, place, or period, the more favourable Arthropod food supply of agricultural habitats was one of the motivating factors for the habitat change of Great Bustard, and even today it is one of the explanations for the settlement and nesting of Great Bustards on arable land. (7) The examination of the Arthropod food sources of the Great Bustard showed that the Arthropod resource sets of the agricultural habitats are still suitable for the maintenance of Great Bustard populations. (8) Environmentfriendly farming, the restrained use of chemicals, and the increase in the diversity of food weeds increase the diversity and mass of phytophagous Arthropods and their predators, thus increasing the resources of the habitat.

Biased adult sex ratios in Western Europe populations of Little BustardTetrax tetraxas a potential warning signal of unbalanced mortalities

SummaryAdult sex ratios (ASRs) have proved to correlate with population trends, which make them potential useful indicators of a species’ population trajectory and conservation status. We analysed ASRs and proportion of juveniles in flocks of an endangered steppe bird, the Little BustardTetrax tetrax, using surveys made during the non-breeding period in seven areas within its Western European range (one in Portugal, four in Spain, and two in France). We found overall male-biased ASRs, as all the seven surveyed areas showed a male-biased ASR mean value. Five areas were below the threshold median value (female sex ratio = 0.4) considered to be consistent with an increased probability of extinction, according to earlier population viability analyses for the species. We also found a significant positive correlation between female ratio and the proportion of young individuals in the non-breeding flocks surveyed. Our results (strongly male-biased ASRs) support the hypothesis that the viability of Little Bustard populations in Western Europe is threatened by an excess of female mortality, something that should be quantified in the future, and emphasise the value of monitoring sex ratio as a population viability indicator in species where monitoring survival is difficult to achieve.

Assisted Reproduction Techniques to Improve Reproduction in a Non-Model Species: The Case of the Arabian Bustard (Ardeotis arabs) Conservation Breeding Program.

Simple SummaryArtificial reproduction technologies such as artificial insemination and semen cryopreservation are important tools for species conservation and long-term genetic management. As with many bird species, Arabian bustard (Ardeotis arabs) populations are declining and are already extinct in some regions. The International Fund for Houbara Conservation (IFHC) has started a conservation breeding program for the Arabian bustard in the United Arab Emirates (UAE). Birds were housed by pairs to allow natural reproduction. Out of 1253 eggs laid, 1090 were incubated, of which 379 were fertile (i.e., 34.8%). In total, this led to the production of 251 chicks. Due to lower than desired fertility, we introduced assisted reproduction techniques to increase fertility and develop zootechnical knowledge for the species. This paper presents the results of semen collection, artificial insemination, and semen cryobanking in Arabian bustards. Inseminations with both fresh and preserved semen led to a significant increase in fertility to 84.3% of incubated eggs (i.e., 43 out of 51 incubated eggs laid by previously artificially inseminated females). Furthermore, we confirmed the viability of cryopreserved semen and its fertilizing capacity. Our results demonstrate the usefulness of artificial reproduction techniques for the conservation of Arabian bustards and suggest that these techniques can be applied to closely related critically endangered species with a minimum of adaptation.Artificial reproductive technologies are highly valuable for ex situ conservation. While Arabian bustard populations are declining and extinct in some parts of the range, the International Fund for Houbara Conservation in the United Arab Emirates implemented a conservation breeding program. Since 2012, a total of 1253 eggs were laid through natural reproduction, 1090 were incubated and 379 of these were fertile (fertility rate of 34.8%), leading to the production of 251 chicks. To improve fertility and acquire crucial knowledge for other endangered large birds, artificial reproduction was implemented in 2018 using fresh, refrigerated, and frozen sperm. A total of 720 ejaculates were collected from 12 birds. We analysed these samples for concentration, volume, motility score (0 to 5), viability (eosin/nigrosine), length, and morphology. The first age at collection was 35.7 ± 18.8 months, mean volume was 89.2 ± 65.3 µL, mean concentration was 928 ± 731 sptz/mL and mean motility score was 2.61 ± 0.95. Morphology analyses revealed a bimodal distribution of sperm length. Five hundred and thirty-five ejaculates were cryopreserved and the initial motility score was 3.4 ± 0.7 and 2.0 ± 0.6 after thawing, while the percentage of normal and intact membrane sperm cells decreased from 88.8 ± 7.5% to 52.9 ± 1%. Sixty-five artificial inseminations were performed, leading to a global fertility rate of 84.3%—more precisely, 85.2% and 83.3%, respectively, for fresh and cryopreserved semen. All methods successfully produced fertile eggs, indicating that artificial insemination is an efficient tool for the conservation and genetic management of the species.

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.

Patterns of abundance reveal evidence of translocation and climate effects on Houbara bustard population recovery

AbstractPopulation reinforcement, through translocations of individuals, aims to restore populations of threatened species. The increase in population size or geographic distribution is often used as positive facts when assessing the recovery of a species, making abundance monitoring a major criterion. Based on 8‐year monitoring of a reinforced population of North African Houbara bustard (Chlamydotis undulata undulata), over an area of 50 170 km² in the eastern region of Morocco, we assessed the success of management actions by assessing spatial and temporal variation in abundance as well as the factors driving this variation. We used count data to estimate and spatialize population abundance. We then assessed environmental (climate) and management covariates (release effort and hunting management) associated with temporal and spatial variation in abundance. The overall estimate of abundance in the study area was 16 918 individuals (95% CI = 13 629–21 027) over our study period, with strong variation between years (range = 10 409–32 401). Our results highlighted strong spatial heterogeneity over the study area, linked to spatial variation in local climate and management conditions. Local abundances were negatively associated with local temperature, were higher in hunting than in non‐hunting areas, and were positively influenced by the number of birds released around the focal point. In addition to describing the spatio‐temporal variation in the abundance of the species on a large scale, we estimated two major proxies of its conservation status: population size and population trend. The determination of these proxies and the comparison with the counterfactual state of the species confirms the beneficial impact of the restoration and protection program on the dynamics of the North African Houbara bustard, while underlining the dependence of these dynamics on ongoing management.

The Perilous Plight of Great Indian Bustard (<i>Ardeotis nigriceps</i>) in the Thar Desert of Rajasthan

This paper summarizes the population dynamics and distribution of the Great Indian Bustard (Ardeotis nigriceps), in the Thar Desert of Rajasthan from 2018 to 2020. The Scan and focal sampling along with the intensive seasonal survey methodology was adopted to assess the population dynamics and movement pattern of the state bird of Rajasthan. The entire study area is divided into 231 grids consisting of 3 blocks and covered using a transect of 3875.49 km, which helped systematic assessment of the Great Indian Bustard (GIB) population. A total of 54 potential grids for GIB has been identified based on the presence and absence of the species and associated habitat of the region. The authors had observed 42 distinct GIB individuals and a record sighting of 11 GIB in a flock at the Thar landscape of Rajasthan. This paper depicts the importance of seasonal migration, and land use utilization for GIB. Authors had also identified two distinct resident populations of GIB i.e. one each from the Khetoloi-Ramdevra belt and Sudashree-Chohani-Sipla belt. The paper had implicated the transboundary movement of this bird towards the Cholistan Desert of Pakistan and raises concern over the same.

Are trellis vineyards avoided? Examining how vineyard types affect the distribution of great bustards

A significant restructuring of vineyards is currently taking place in the European Union (EU) as a result of the implementation of a restructuring and conversion of vineyards regulation (CE 1493/1999) in southwest Europe, so that trellis vineyards are rapidly replacing traditional vineyards (e.g., surface area from 18.1 % in 2010 to 34 % in 2015 in Castilla-La Mancha, Central Spain). These changes may influence patterns of space use in birds, which may avoid modified habitats. We assess how the location of traditional and trellis vineyards might influence the distribution of great bustard (Otis tarda), a globally threatened species. We estimate Resource Selection Functions (RSFs) to quantify the relative probability of use of different areas by the great bustards, and use the RSF’s to simulated scenarios of conversion from traditional to trellis vineyards (low - 10 %, medium - 30 %, and high rate - 60 %) to quantify the potential impact of such modifications on the availability of suitable great bustard habitat. Our results revealed that great bustards significantly avoid trellis vineyards, especially at closer distances. Transition scenarios show how an increase in the proportion of traditional vineyards converted to trellis vineyards greatly decrease the proportion of suitable habitat for great bustard. Compared to current conditions, the percentage loss of suitable habitat increased steadily with higher rates of converted vineyards, up to 60 % loss of suitable habitat at the highest rate of conversion. Because the effect of transforming traditional vineyards to trellis vineyards depends both on the amount of habitat available for bustards before the transformation occurs and on the overall area covered by vineyards, a correct estimation of transformable vineyard area will require a case-by-case assessment to assure a low impact on bustard populations. We identified alternative vineyard management options that would mitigate impacts on the great bustard populations.

Inter-individual consistency in habitat selection patterns and spatial range constraints of female little bustards during the non-breeding season

BackgroundIdentifying the factors that affect ranging behavior of animals is a central issue to ecology and an essential tool for designing effective conservation policies. This knowledge provides the information needed to predict the consequences of land-use change on species habitat use, especially in areas subject to major habitat transformations, such as agricultural landscapes. We evaluate inter-individual variation relative to environmental predictors and spatial constraints in limiting ranging behavior of female little bustards (Tetrax tetrax) in the non-breeding season. Our analyses were based on 11 females tracked with GPS during 5 years in northeastern Spain. We conducted deviance partitioning analyses based on different sets of generalized linear mixed models constructed with environmental variables and spatial filters obtained by eigenvector mapping, while controlling for temporal and inter-individual variation.ResultsThe occurrence probability of female little bustards in response to environmental variables and spatial filters within the non-breeding range exhibited inter-individual consistency. Pure spatial factors and joint spatial-habitat factors explained most of the variance in the models. Spatial predictors representing aggregation patterns at ~ 18 km and 3–5 km respectively had a high importance in female occurrence. However, pure habitat effects were also identified. Terrain slope, alfalfa, corn stubble and irrigated cereal stubble availability were the variables that most contributed to environmental models. Overall, models revealed a non-linear negative effect of slope and positive effects of intermediate values of alfalfa and corn stubble availability. High levels of cereal stubble in irrigated land and roads had also a positive effect on occurrence at the population level.ConclusionsOur results provide evidence that female little bustard ranging behavior was spatially constrained beyond environmental variables during the non-breeding season. This pattern may result from different not mutually exclusive processes, such as cost–benefit balances of animal movement, configurational heterogeneity of environment or from high site fidelity and conspecific attraction. Measures aimed at keeping alfalfa availability and habitat heterogeneity in open landscapes and flat terrains, in safe places close to breeding grounds, could contribute to protect little bustard populations during the non-breeding season.

Long lasting breeding performance differences between wild-born and released females in a reinforced North African Houbara bustard (Chlamydotis undulata undulata) population: a matter of release strategy

The success of translocation programmes is reflected by the ability of translocated individuals to survive and reproduce in their new environment. However, it has previously been reported that translocated individuals have lower demographic performance than their wild-born conspecifics, due to management and individual factors (such as release conditions or age). Here, we study six breeding parameters in free-ranging females of the North African Houbara bustard (Chlamydotis undulata undulata) and compare these parameters between captive-bred released (n = 204) and wild-born (n = 101) birds, considering the age of individuals and the period of release (autumn versus spring). Our results indicate that (1) captive-bred released females successfully breed in the wild; (2) for three out of the six breeding parameters studied, released females show lower performances than wild-born females; but, (3) Although we observed consistently reduced breeding performances in 1 year old females relative to older females, we did not uncover any interaction between age and the origin of females, suggesting that the impairment of breeding parameters in released females is long lasting; and, (4) interestingly, this impairment of breeding parameters depends on the period of release, with lower breeding performances for spring releases compared to autumn releases. Overall, our study highlights the capacity of captive-bred females to reproduce in the wild, contributing to the dynamics of the population beyond their individual history. Our results also uncover complex variations of breeding parameters in translocated birds, but suggest that these differences can be minimized through an appropriate translocation strategy.

The Probable Strong Decline of the Great Bustard Otis tarda tarda Population in North-Western China

The Great Bustard population in Xinjiang Province, the Chinese stronghold of Otis tarda tarda, is suspect to be declining, but little is known about its trends and numbers. Using the same methods, we compared two former published counts from the province (1988 and 1992) with ours (2013–2016), exhaustively covering the two known bustard areas of Tacheng (summer) and Qapqal (winter). A strong decline (92%) is reported, with a minimum 19 birds found in Tacheng and none in Qapqal. Cooperation between scientists is needed to study the causes of decline in O. T. tarda in Xinjiang and elsewhere.—Wang, M., Gonzalez, M.A., Yang, W., Neuhaus, P., Blanco-Fontao, B. & Ruckstuhl, E.K. (2018). The probable strong decline of the Great Bustard Otis tarda tarda population in north-western China. Ardeola, 65: 291–297.

EU protected area network did not prevent a country wide population decline in a threatened grassland bird.

BackgroundFew studies have assessed the effectiveness of the Protected Area networks on the conservation status of target species. Here, we assess the effectiveness of the Portuguese Natura 2000 (the European Union network of protected areas) in maintaining a species included in the Annex I of the Bird Directive, namely the population of a priority farmland bird, the little bustard Tetrax tetrax.MethodsWe measured the effectiveness of the Natura 2000 by comparing population trends across time (2003–2006 and 2016) in 51 areas, 21 of which within 12 Special Protection Areas (SPA) that were mostly designated for farmland bird conservation and another 30 areas without EU protection.ResultsOverall, the national population is estimated to have declined 49% over the last 10–14 years. This loss was found to be proportionally larger outside SPA (64% decline) compared to losses within SPA (25% decline). However, the absolute male density decline was significantly larger within SPA .DiscussionIn spite of holding higher population densities and having prevented habitat loss, we conclude that Natura 2000 was not effective in buffering against the overall bustard population decline. Results show that the mere designation of SPA in farmland is not enough to secure species populations and has to be combined with agricultural policies and investment to maintain not only habitat availability but also habitat quality.

Tracking data of the Little Bustard Tetrax tetrax in Iberia shows high anthropogenic mortality

SummaryThe Little Bustard Tetrax tetrax (Linnaeus, 1758) is a medium-sized, ‘Near Threatened’ steppe bird, whose Iberian population has been alarmingly declining over recent decades. Although this population loss has been mainly attributed to agricultural intensification, there is no information on Little Bustard adult mortality levels and their drivers. Based on a joint effort combining all the tracking data on adult Little Bustards collected over a period of 12 years by all research teams working with the species in Iberia, we found that annual anthropogenic mortality is likely to have a critical impact on the species, with values almost as high as the mortality attributed to predation. Collision with power lines was found to be the main anthropogenic threat to the adult population (3.4–3.8%/year), followed by illegal killing (2.4–3%/year), which had a higher impact than initially foreseen. Our work shows how poorly understood and previously unknown threats are affecting the survival of the most important Little Bustard population in Europe.

Evidence of reproductive senescence of released individuals in a reinforced bird population

In free-ranging populations, age-dependent variation in fitness related parameters, in particular the pattern of senescence, has major eco-evolutionary implications and potential influence on population dynamics. Despite the recent surge of studies of senescence in the wild, senescence patterns in species for which population dynamics assessments are crucial, such as translocated populations, remain virtually unexplored. Based on a 15-year nest survey of a North-African Houbara bustard population in Morocco, we investigated age variation in the breeding performance of captive-bred females released in the wild. We identified 781 females, from 1 to 10years of age, on 1094 nests. We examined how age influenced nest initiation date, clutch size, egg volume, daily nest survival and daily brood survival, as well as whether age-dependent patterns varied according to environmental conditions. Most breeding parameters exhibited variation, suggesting an increase in breeding performance with age in young females (those from 1 to 3years old). In older females (>7–8years old), the egg volume and clutch size decreased with age, in concordance with expectations from senescence theories and previous empirical results obtained from captive Houbara bustards. Finally, our analysis uncovered a significant interaction between age and the amount of precipitation prior to the breeding season on clutch size, suggesting differential abilities of females of different ages to increase their breeding investment. Our study suggests that life histories in translocated individuals are not affected by translocation protocols and provides insights for implementing age dependencies in population viability assessments.

Abundance dynamics of the Trans-Volga great bustard (Otididae, Aves) population

The results of our study of the abundance dynamics of the great bustard population in the southern part of the Saratov Trans-Volga region for the period from 1998 to 2015 are presented on the basis of censuses carried out before the migration for wintering in the fall and on leks in the spring. The abundance dynamics was analyzed, and the factors causing it were identified. Data on the distribution of the great bustard population density over an account area of 12000 km2 are presented.

Impacts of land use and infrastructural changes on threatened Little Bustard Tetrax tetrax breeding populations: quantitative assessments using a recently developed spatially explicit dynamic modelling framework

SummaryWith the combination of worldwide landscape changes and the uncertainty about the impact on species abundance and distribution, the value of spatio-temporal modelling tools is increasingly obvious. The Little Bustard Tetrax tetrax breeds on low-intensity arable cultivation and pastoral land and is currently threatened by diverse landscape modifications. The aim of this research was to predict Little Bustard population trends in the face of realistic scenarios of land use and infrastructure changes, applying a recently developed spatially explicit framework, based on the stochastic dynamic methodology (StDM). The application of this approach provided some basis to analyse the responses of breeding populations’ spatial distribution and abundance to the scenarios implemented. Since some of these scenarios represent local and/or regional risks to the viability of Little Bustard breeding populations, the results obtained demonstrate the potential of the proposed framework for landscape planning in the scope of the conservation of this threatened species. This approach also provides a promising baseline to support ecological risk assessments for other species, derived from ecological models with increased predictive power and intuitiveness to decision makers and environmental managers.

Assessing the extinction risk of the great bustard Otis tarda in Africa

We studied the dynamics and trend of the last extant population of great bustards Otis tarda in Africa. Moroccan great bustards are the southernmost population of this species, and thus show the characteristics of a peripheral population: small size, isolation and low gene flow. Available counts indicate a severe population decline (62% in the last 15 yr), as well as a contrac- tion of the species' distribution. We used a population viability analysis (PVA) to evaluate the quasi-extinction risk and to identify the most important threats. The estimated geometric growth rate of the more realistic of a set of possible scenarios was 0.87 (95% CI: 0.85, 0.89). This implies a 13% annual decline over 50 yr. However, projections derived from these results should be inter- preted with caution, because models have a great deal of uncertainty and vital rates from Iberian populations may be different from those of the Moroccan population. PVA showed the negative consequence of human-induced mortality. According to the model that best fits our census data and if present threats remain in the coming years, this peripheral population could go extinct in ca. 20 yr. Agricultural intensification, infrastructure developments and new power lines in rural areas where the species occurs are causing habitat destruction and fragmentation and increasing artifi- cial mortality. Urgent conservation measures, especially to reduce human-induced mortality, are needed to save African great bustards from extinction. We suggest that these findings can be gen- eralized to other peripheral great bustard populations living in highly humanized landscapes.

Impacts of survival and reproductive success on the long-term population viability of reintroduced great bustards Otis tarda in the UK

AbstractReintroductions aim to re-establish species within their historical ranges through the release of wild- or captive-bred individuals following extirpation (or extinction) in the wild. There is no general agreement on what constitutes a successful reintroduction but the probability of the population achieving long-term persistence should be addressed. Here we review a 10-year trial reintroduction of the great bustard Otis tarda, a globally threatened bird species, to the UK and assess the long-term population viability. Despite changes in rearing and release strategy, initial post-release survival probability remained consistently low, with only 11.3% of bustards (n = 167) surviving from release to 1 year post-release. Nineteen breeding attempts were made by eight females; however, only one chick survived > 100 days after hatching, and no wild juveniles have recruited into the population. Using demographic rates from the UK population and wild populations elsewhere, and stochastic population modelling, we investigate the viability of this reintroduced population by predicting population size over the next 10 years. Under current demographic rates the population was predicted to decline rapidly. Self-sufficiency was predicted only using the highest estimates from the UK population for first-year and adult survival, and recruitment rates from wild populations elsewhere. Although changes have been made in rearing, release strategies, habitat management and release sites used, these changes appear to have a modest effect on long-term viability. Substantial improvements in survival rates and productivity are necessary to establish a viable great bustard population in the UK, and we consider this unlikely.