Vol. 45: 55–69, 2021 ENDANGERED SPECIES RESEARCH Published May 27 https://doi.org/10.3354/esr01126 Endang Species Res OPEN ACCESS Devil is in the detail: behaviorally explicit habitat selection by the Critically Endangered great Indian bustard Sutirtha Dutta*, Yadvendradev Jhala Department of Animal Ecology Conservation Biology, Wildlife Institute of India, Chandrabani PO Box 18, Dehradun 248001, India ABSTRACT: Habitat management to accommodate ecological needs of threatened species can help abate biodiversity decline. Some species require contrasting microhabitats for different func- tions, and may prefer patches with ample, diverse microhabitats. We examined this problem for the Critically Endangered great Indian bustard Ardeotis nigriceps in 175 km2 breeding habitat in Kachchh, India. We developed behaviorally explicit resource selection functions (RSFs) by com- paring used vs. available microhabitats using binomial generalized linear models that tested hypothesized habitat responses in an information theoretic framework. We identified suitable resource units based on fitted RSF values. We examined if availability of complementary resource units influenced density/usage at the patch level, using line transect distance sampling. Birds pre- ferred agro-vegetation mixture, grassland, high fruit abundance and intermediate grazing den- sity, and they avoided Prosopis thickets for foraging. They preferred moderately tall sward for day resting but shorter sward and less Prosopis for roosting. Nesting females preferred grasslands with relatively tall sward and abundant insects, while displaying males preferred grasslands with shorter sward, far from settlements. Thus, microhabitat selection differed between behaviors and differed from habitat availability. The RSF without behavioral segregation failed to capture these nuances and was non-informative for habitat management. Density/usage at the patch level was correlated with the availability of complementary microhabitats. Thus, protected area manage- ment to accommodate diverse life-history requirements may reduce species’ movements over large hostile landscapes and associated mortality. Overall, species requiring complementary microhabitats will benefit from management that promotes habitat heterogeneity. However, habi- tat use analysis based on behaviorally inexplicit occurrence cannot capture the habitat quality of such species. KEY WORDS: Ardeotis nigriceps · Conservation · Grasslands · Habitat restoration · Behavior · Foraging · Resource selection function · Distance sampling 1. INTRODUCTION ma nipulation can abate these trends. Hence, under- standing resource selection and supplementing pre- Fourteen percent of the world’s birds are threatened ferred resources in breeding areas have benefited (IUCN 2018), with particularly steep declines among many birds. For instance, a study highlighting the im- Indo-Malayan species (Butchart et al. 2004). Reduced portance of tall marsh vegetation and late mowing for fitness in altered habitats has caused much of these corncrake Crex crex (Green 1996) recommended ac- de clines (Tilman et al. 1994), but corrective habitat tions such as delayed mowing that facilitated the re- © The authors 2021. Open Access under Creative Commons by *Corresponding author: [email protected] Attribution Licence. Use, distribution and reproduction are un - restricted. Authors and original publication must be credited. Publisher: Inter-Research · www.int-res.com 56 Endang Species Res 45: 55–69, 2021 covery of this species (O’Brien et al. 2006). However, vation applications (Boyce & McDonald 1999). These information on habitat use is lacking for many threat- statistical models can explain species−habitat rela- ened species. This is particularly concerning for grass- tionships and predict where species are distributed, lands that are rapidly changing and require urgent and they are frequently applied to manage habitats conservation interventions (White et al. 2000). Bird of endangered species (Rushton et al. 2004). Despite populations are declining faster in grasslands than the growth of resource selection analysis, even in - other biomes of many regions owing to habitat loss, af- volving machine learning approaches (Shoemaker et forestation, mismanagement, land-use intensification al. 2018), their application is not behaviorally expli - and fragmentation (Hovick et al. 2014, SoIB 2020). cit. Their inferences can be biased towards more de - Grassland birds may select complementary habitats tectable behaviors, ignore resource requirements for to meet their diverse ecological needs (Law & Dick - elusive behaviors and run the risk of recommending man 1998). Habitat selection differs between nesting measures that do not encompass the diversity of eco- and feeding usage for short-toed larks Ca landrella logical needs of a species. Rahmani (1989) qualitati - brachydactyla (Serrano & Astrain 2005) and black vely described different microhabitats used by great kites Milvus migrans (Sergio et al. 2003). Hence, habi- Indian bustards. However, a comprehensive assess- tat choice should be assessed across multiple behav- ment of the species’ resource selection across behav- iors and scales for comprehensive understanding and iors, and the interplay of space-use decisions across holistic management. Species depend on landscape scales, is lacking. These insights will directly help in complementation when their abundance at larger designing and managing their breeding habitats. scales is constrained by the availability of comple- Here, we examined habitat selection by great In - mentary resources at smaller scales (Dunning et al. dian bustards in a semiarid multiple-use landscape, 1992). For these species, availability of complemen- to demonstrate how to manage breeding reserves. tary resources can enable higher usage of an area, by Specifically, we asked: (1) Do these birds select dif- reducing energetic costs of movements, diminishing ferent habitats at fine-grained scales (hereafter predation risk and attracting birds (Choquenot & Rus- referred to as microhabitat or resource units) to fulfil coe 2003). Alternatively, usage by birds may be con- their daily ecological needs, and what are the impli- centrated if complementary resources are available in cations for resource selection studies that ignore proximity, but diffused over a larger area if comple- these behavioral differences? (2) Does density/usage mentary resources are spatially disjoint. Bustards (number of birds per unit area) at larger grain sizes (family Otididae), a group of globally threatened depend on the availability of complementary grassland birds, offer an ideal system to test this pos- resource units at finer scales such that strategic inser- tulate because of their requirement for heterogeneous tion of missing resource units can promote greater habitats and growing de pendence on conservation patch usage? To this end, we collected microhabitat efforts (Collar et al. 2017). data from 100 m radius plots at locations used by The great Indian bustard Ardeotis nigriceps is Criti- great Indian bustards for foraging, day resting, night cally Endangered with around 100−150 birds left in In- roosting, courting and nesting, along with available dia and Pakistan (Dutta et al. 2011, BirdLife Inter- (random) locations. We developed resource selection national 2018). Its habitats, mainly arid−semiarid functions (RSFs) for each behavior and a common grass lands, are marginalized as ‘unproductive waste- RSF for all behaviors by testing ecological predic- lands’ and are experiencing infrastructural develop- tions with used vs. available habitat data using bino- ment and intensive land uses (Dutta 2018). The Indian mial generalized linear models (GLMs) in an infor- government is implementing recovery actions for this mation-theoretic framework (Man ly et al. 2002). We species that include re storation of breeding habitats compared inferences be tween behaviorally explicit (Dutta et al. 2013). En closures are being established in and common RSFs, to answer the first question. For Thar (Rajasthan), Kachchh (Gujarat) and other range the second question, we classified random locations areas, to reduce anthropogenic disturbances, increase as ‘suitable’ or ‘un suitable’ for a behavior based on herbaceous cover and improve breeding success. fitted RSF values, and computed microhabitat diver- Since the species faces high mortality risk due to sity at a larger scale (transects) from the frequency of power-line collisions, habitat management to increase ‘suitable’ locations for various behaviors. Finally, we bird density/ usage in infrastructure-free protected en- examined if the spe cies’ density in transects, esti- closures can aid in the recovery of this species. mated using distance sampling (Burnham et al. Inferences on habitat suitability by comparing used 1980), depended on microhabitat diversity, using vs. available locations have a long history in conser- GLM. Dutta & Jhala: Habitat selection by great Indian bustards 57 2. MATERIALS AND METHODS (Dutta 2012). The regional climate is semiarid with high temperature variations (0−5°C in January to 2.1. Study area 40−45°C in May) and scant rainfall (mean 384 mm, range 78−888 mm during 2000−2010). Tropical thorn We conducted fieldwork from 2007 through 2011 in forest/scrub and grasslands (Champion & Seth 1968) Abdasa tehsil (precinct) of Kachchh, Gujarat, India. are grazed by free-ranging livestock, and are inter- This landscape harbors a small and declining popu-