Factors Influencing Habitat Selection Research Articles

Multi‐scale resource selection and spatial ecology of the Indian fox in a human‐dominated dry grassland ecosystem

Resource selection by animals is a scale-dependent hierarchical process of behavioural responses to environmental factors. Lack of information on such habitat selection dynamics can hamper the conservation management of species and habitats. For example, little is known about the space-use patterns of species in the semi-arid grasslands of peninsular India. The Indian fox Vulpes bengalensis, a poorly studied, yet reportedly widespread carnivore of the Indian subcontinent, represents an example of such lack of information. We determined the factors influencing habitat selection by Indian foxes at two levels in a multiple-use human-dominated landscape. Indian foxes are found in the highest densities in dry-grassland habitats, but are also reported to be opportunistic omnivores. Thus, we hypothesized that foxes select mainly for native grassland over human-modified habitats at a landscape level, but may not avoid human-modified habitats at the home-range level to take advantage of increased rodent availability in agricultural areas. We analysed radio-telemetry data from 32 Indian foxes using (1) a utilization distribution-weighted compositional analysis to determine the main components of home-range selection at the landscape level; (2) a discrete-choice analysis to determine the factors influencing the selection of habitat within the home ranges. At the landscape level, Indian foxes selected for native grasslands, forestry plantations and fallow land over human-dominated habitats such as agricultural land and human settlements. The presence of native grasslands was also the dominant predictor of habitat selection at the home-range scale across all seasons. Our results show that natural grasslands are the most important predictor of space use at multiple scales. This has important conservation implications as the threatened semi-arid short grasslands are poorly represented in India's protected area network. Although Indian foxes are not currently considered endangered, failure to conserve remaining native grassland habitats may threaten this species along with other grassland obligates.

Breeding Habitat Selection of Reeves's Pheasant (<I>Syrmaticus reevesii</I>) in Dongzhai National Nature Reserve, Henan Province, China

Reeves's Pheasant (Syrmaticus reevesii) is a threatened pheasant species endemic to China. The habitat use of territorial male birds was surveyed by the help of live decoys in a core area of Dongzhai National Nature Reserve. The breeding habitat selection of this pheasant was examined at two scales (115 m and 250 m scale, i.e. 4.15 hm(2 ) and 19.63 hm(2 ), respectively), including the characteristics at distance scale. Investigation was based on line transect, RS and GIS in Dongzhai National Natural Reserve from 2001 to 2003. Moreover, a range of habitat variables were compared between used and control points at each scale, and stepwise logistic regression was applied to select the key scale and the key habitat factors in relation to breeding habitat selection of this bird. Our results stated that the territorial males at Baiyun occurred mostly in mixed forests, followed by fir forests, pine forests, shrubs, and broadleaf forests. The area of conifer forests was the key factor influencing habitat selection of this bird in breeding period at the scales of 115 m and 250 m, and the proximity of farmland was important for habitat selection in breeding seasons. Furthermore, Reeves's Pheasants attached great importance to the scale of 115 m. When considering a range of habitat variables at all scales within a multivariate regression, the leading factors having effect on habitat selection in the breeding period were areas of conifer forests at 115 m scale and the distance to farmland. In addition, these above results suggested that strengthening the management of suitable habitat, and optimizing the habitat configuration are important in promoting conservation of this bird. However, it also highlighted the importance of initiating future researches on the conifer forests and their impact on the population of Reeves's Pheasants, which would be beneficial to promote the habitat conservation of this pheasant more effectively.

Stochasticity as an alternative to deterministic explanations for patterns of habitat use by birds

Stochasticity is rarely explicitly investigated as a determinant of patterns of habitat use, even though evidence of its influence would undermine support for deterministic models of habitat selection. To assess the role of stochasticity in generating patterns in habitat use, we compared observed patterns of year‐to‐year variation in habitat use of 20 bird species over five years with patterns randomly generated from null models with different biological constraints (i.e., abundance, territoriality, exclusion of unused habitat, site fidelity, and habitat preference). We were able to recreate patterns of variability in spatial distributions with one or more null models for 18 species, suggesting an important role of stochasticity. Although year‐to‐year variability could be modeled as a purely stochastic process for only four species, null models in which random variability was constrained by the influences of vegetation or site fidelity collectively matched the observed patterns of variability of all 18 species. Support for these two models suggested that factors that increase the likelihood of returning to a previously used area and thus limit the spatial extent of random territory placement can generate patterns similar to those we observed. Greater support for models with preference constraints (i.e., models that included bird–vegetation associations) over models with avoidance constraints (i.e., models that excluded areas that were never occupied) indicated that preference was the primary mode of habitat selection. Stochastic patterns in habitat use may have resulted from a weak relationship between habitat selection and habitat quality, influence of non‐vegetation habitat features (e.g., climatic fluctuations), nonequilibrium conditions, and a greater influence of stochastic variation at small spatial and temporal scales. Alternatively, responses to environmental cues may have been deterministic, but in summation, these responses may have created variability in spatial distribution patterns that was indistinguishable from random variation. In such cases, we suggest that it may be easier to model variation in habitat use as a random process rather than using deterministic models that account for a multitude of environmental factors influencing habitat selection of birds. Regardless, stochasticity may play a larger role in generating patterns of habitat use than is often considered, and it deserves wider attention.

Population size, breeding performance and habitat use of the Black-winged Pratincole Glareola nordmanni

SummaryThe population of the Black-winged Pratincole Glareola nordmanni has declined significantly during the course of the 20th century, resulting in a classification as ‘Near Threatened’ and ‘Endangered’ in the Global and European Red Data Books, respectively. Reasons for the decline are largely unknown due to a lack of information on the breeding ecology of the species. We studied breeding performance and habitat use of the Black-winged Pratincole in two areas in Kazakhstan and evaluated a new world population estimate. Colony size ranged from two to 180 pairs and differed significantly between the study areas. Mean breeding success was 1.30 ± 0.16 (mean ± SE) fledged chicks per breeding pair in Central Kazakhstan, and 0.59 ± 0.13 (mean ± SE) fledged chicks per breeding pair in NE Kazakhstan. Habitat types preferred were intensively grazed natural steppe, abandoned and fallow fields, shores of freshwater and brackish lakes and solonchaks (salt pans). Factors influencing habitat selection were quantified the first time for this species: the probability of occurrence of breeding colonies was highest near human settlements, within 3km of open water and where sward heights were low or intermediate, indicating a reliance on heavy grazing and water.Using data from six surveys across the whole breeding range, we calculated a new world population estimate of 76,000–95,000 breeding pairs, which is substantially higher than previous estimates. We discuss colony size, habitat use and population trends in the light of changing landscape conditions in the steppe zone and suggest an increase in habitat available to Black-winged Pratincole due to an increase in the area of fallow fields and a change in grazing regimes since the collapse of the Soviet Union in 1991.

The influence of river functionality on habitat selection by Ephemeroptera in spatially and temporally diverse lowland rivers, with particular reference to the River Bug

Abstract The purpose of this work is the designation of changes in the environmental preferences of mayflies in the prevailing conditions in a large lowland river little changed by human activity. During the study, the occurrence of the following species were recorded: Cercobrachys minutus (54.2%); Procloeon nana (24.5%); Pseudocentroptiloides shadini (7.6%); Ametropus fragilis (2.9%), which were numerously represented and formed a permanent element of the fauna, and Baetopus wartensis (0.1%) and Oligoneurisca borysthenica which were noted very rarely and were accidental species. The differences and similarities in the functionality of the psammophilous and other mayfly assemblages were assessed. The data from the last fifteen years of study was investigated and compared with those from other rivers which were more managed. PCA was used to distinguish the main factors influencing habitat selection at particular stages of life history and the tendency for drifting.

Improving the value of field margins as foraging habitat for farmland birds

1. Uncropped field margins are important foraging habitats on farmland for many declining bird species and are a key component of Agri-Environment Schemes across Europe. Maximizing the value of foraging habitats requires detailed knowledge of the factors influencing habitat selection and food availability. 2. We firstly conducted an observational study of foraging habitat selection by breeding yellowhammers Emberiza citrinella L. on lowland mixed farmland, in relation to underlying invertebrate and vegetation characteristics. 3. There was a clear seasonal shift in the relative use of field margins and cereal crops. Margins were used less than crops in late summer, despite supporting higher invertebrate abundance relative to cereals. Seasonal increases in vegetation height were most marked in margins, suggesting the seasonal decline in margin use may reflect reduced food accessibility. 4. In the second phase of the study, field margins were cut experimentally to create short, open patches within taller margin swards. The use of cut patches by foraging yellowhammers increased significantly between early and late summer, and patches were used more frequently with increasing height of adjacent uncut margin. These findings strongly support the theory that tall vegetation reduces margin accessibility in late summer. 5. Synthesis and applications. Provision of invertebrate-rich field margins is a core component of Agri-Environment Schemes, but current prescriptions may result in them having limited value in late summer. More effective management, such as more frequent cutting, may be required to maximize the benefits for foraging birds by creating short, open vegetation patches. Measures to increase accessibility to invertebrates on farmland are likely to benefit a range of bird species across a variety of crop types.

Fine-scale habitat selection by adult female swamp wallabies (Wallabia bicolor)

Animals typically use habitat in a non-random way, but the factors influencing habitat selection may change throughout the 24-h cycle. In this study, we quantified resources at used and available locations to test two predictions about the fine-scale habitat selection of seven adult female swamp wallabies (Wallabia bicolor). We predicted that selection would be (i) non-random and (ii) differ between diurnal and nocturnal periods with respect to both food and shelter. Variables quantifying food abundance and lateral cover were recorded at 56 diurnal, 17 nocturnal and 143 randomly selected available locations. Logistic regression indicated that diurnal habitat selection was positively correlated with lateral cover, and the cover of trees, shrubs and forbs, whereas nocturnal selection was positively correlated with forb cover only. Diurnal locations had more lateral cover than nocturnal locations. The data were consistent with our first prediction, but only partially supported our second. At a fine scale, diurnal habitat selection was influenced by the co-availability of shelter and food resources, whereas nocturnal selection was influenced by food availability only, indicating that factors influencing habitat selection changed throughout the 24-h cycle.

Conspecific Attraction is a Missing Component in Wildlife Habitat Modeling

Abstract Wildlife biologists use knowledge about wildlife‐habitat relationships to create habitat models to predict species occurrence across a landscape. Researchers attribute limitations in predictive ability of a habitat model to data deficiencies, missing parameters, error introduced by specifications of the statistical model, and natural variation. Few wildlife biologists, however, have incorporated intra‐ and interspecific interactions (e.g., conspecific attraction, competition, predator‐prey relationships) to increase predictive accuracy of habitat models. Based on our literature review and preliminary data analysis, conspecific attraction can be a primary factor influencing habitat selection in wildlife. Conspecific attraction can lead to clustered distributions of wildlife within available habitat, reducing the predictive ability of habitat models based on vegetative and geographic parameters alone. We suggest wildlife biologists consider incorporating a parameter in habitat models for the clustered distribution of individuals within available habitat and investigate the mechanisms leading to clustered distributions of species, especially conspecific attraction.

Influence of thermal fronts on habitat selection by four rorqual whale species in the Gulf of St. Lawrence

Understanding the factors influencing habitat selection is critical to improving manage- ment and conservation plans for large whales. Many studies have linked the distribution of cetaceans to basic environmental features such as underwater topography and sea surface temperature (SST), but the mechanisms underlying these relationships are poorly understood. Dynamic mesoscale pro- cesses like thermal fronts are prime candidates to link physiographic factors to whale distribution because they increase biological productivity and aggregate prey. However, previous studies of large whales have found little evidence of such associations, possibly because they were not at the appro- priate spatio-temporal scales. We quantified the relationship between SST fronts and the distribution of blue Balaenoptera musculus, finback B. physalus, humpback Megaptera novaeangliae and minke B. acutorostrata whales in the northern Gulf of St. Lawrence. We compared the distribution of 1094 whale sightings collected from boat surveys conducted in 1996 to 2000 to the locations of frontal areas determined from 61 satellite maps. The distributions of whales and thermal fronts were highly corre- lated (random resampling and Mantel tests of matrix similarity). Spatial distributions differed among species, probably reflecting differences in feeding strategies. Identification of surface fronts from satellite imagery thus effectively complemented field observations of whales. These findings signifi- cantly increase our understanding of habitat quality in rorqual whales, and encourage a greater use of dynamic environmental variables in future studies of whale habitat use.

The potential impact of tourism development on habitat availability and productivity of Malaysian plovers Charadrius peronii

Summary Increased human pressure on coastal habitats has contributed to the global population decline in waders. Although coastal development can be particularly rapid and poorly regulated in tropical countries, very little research has been conducted to assess the extent of these impacts in the tropics. We examined the potential effects of human disturbance and tourism‐related habitat changes on Malaysian plovers breeding on sandy tropical beaches. In 2004 and 2005, we monitored 54 and 79 pairs of Malaysian plovers in the Gulf of Thailand, and used logistic habitat models to identify factors influencing habitat selection and breeding success. These models included variables affected by anthropogenic changes such as human disturbance and vegetation structure, as well as other natural factors such as prey availability and predator densities. We also assessed causes of nest failure and conducted 372 h of behavioural observations to identify mechanisms that relate important habitat variables to plover productivity. Plovers selected wide beaches with low levels of human disturbance that had a low percentage cover of tall trees backing the beach. The likelihood of hatching clutches and fledging chicks was greater in territories with low levels of human disturbance, low conspecific density and high percentage cover of 0·5–5 m tall vegetation backing the beach. Nest monitoring and behavioural observations suggested that heightened vulnerability to tidal inundation, trampling, heat stress, predators and territorial conflicts may have contributed to the results from the habitat models. We conclude that tourism development on Thai beaches affects both habitat availability and productivity of Malaysian plovers by enhancing beach erosion rates, converting medium vegetation into tall monocultures and intensifying human disturbance. These direct effects of habitat loss may be exacerbated by density‐dependent reductions in productivity. Synthesis and application. This study demonstrates the value of combining three approaches: habitat modelling, nest monitoring and behavioural observations, for identifying impacts of anthropogenic changes on breeding birds and assigning ultimate causes. In understudied regions where there are pressing threats to wildlife, this approach may focus research efforts so that the necessary data can be obtained rapidly in order to assess and predict human impacts.

Habitat selection at multiple spatial scales by foraging Glossy Black‐cockatoos

Abstract: Habitat selection among vertebrates entails decision making at a number of spatial scales. An understanding of factors influencing decisions at each of these scales is required for the effective management of wildlife populations. This study investigates the foraging ecology of a population of Glossy Black‐cockatoos in central New South Wales. We took advantage of the characteristic feeding sign produced by Glossy Black‐cockatoos to examine factors influencing habitat selection at multiple spatial scales. Birds preferred to forage at sites where food was abundant and avoided open sites where the predation risk may be greater. Their two food species,Allocasuarina diminutaandAllocasuarina gymnanthera, differed in profitability (kernel intake rate as measured by the ratio of seed weight to total seed and cone weight), as did trees within a species. Both species were utilized extensively, although foraging intensity was greater at sites where the more profitable species was present. In order to maximize their food intake, birds selected individual trees on the basis of cone abundance and profitability. Cones produced in the previous year were preferred.

Quantitative analysis of bottlenose dolphin movement patterns and their relationship with foraging

1. Broad-scale telemetry studies have greatly improved our understanding of the ranging patterns and habitat-use of many large vertebrates. However, there often remains considerable uncertainty over the function of different areas or the factors influencing habitat selection. Further insights into these processes can be obtained through analyses of finer scale movement patterns. For example, search behaviour may be modified in response to prey distribution and abundance. 2. In this study, quantitative analysis techniques are applied to the movements of bottlenose dolphins, recorded from land using a theodolite, to increase our understanding of their foraging strategies. Movements were modelled as a correlated random walk (CRW) and a biased random walk (BRW) to identify movement types and using a first-passage time (FPT) approach, which quantifies the time allocated to different areas and identifies the location and spatial scale of intensive search effort. 3. Only a quarter of the tracks were classed as CRW movement. Turning angle and directionality appeared to be key factors in determining the type of movement adopted. A high degree of overlap in search effort between separate movement paths indicated that there were small key sites (0.3 km radius) within the study area (4 km(2)). Foraging behaviour occurred mainly within these intensive search areas, indicating that they were feeding sites. 4. This approach provides a quantitative method of identifying important foraging areas and their spatial scale. Such techniques could be applied to movement paths for a variety of species derived from telemetry studies and increase our understanding of their foraging strategies.

Thermal quality influences habitat selection at multiple spatial scales in milksnakes

:Factors influencing habitat selection may be scale dependent, leading to different selection patterns at different spatial scales. By limiting habitat-selection studies to a single scale, important selection patterns could be missed. Despite this danger, many studies investigate habitat selection at a single scale, often ignoring macro-habitat selection: the selection of a home range within the study area. We investigated macro- and micro-habitat selection in milksnakes. Because of the importance of thermoregulation to ectotherms, we predicted that snakes would select habitats of high thermal quality at both microand macro-habitat scales. In 2003–2004, we located 25 individuals 890 times and characterized the habitat in detail at 279 locations used by milksnakes and at 279 paired random locations. Open habitats (fields, rocky outcrops, marshes) and edges have environmental temperatures that deviate less from the preferred body temperature range of milksnakes and offer characteristics that facilitate thermoregulation compared to forest. At the macro- and micro-habitat scales, milksnakes preferred habitats of high thermal quality: they used fields and rocky outcrops more than forests. Milksnakes also preferred edges at both scales. In addition, milksnakes preferred locations with open canopy and many rocks at the micro-habitat scale. These results support the notion that thermal quality influences habitat use in ectotherms and strengthen the idea that habitat-use studies should be conducted at more than one spatial scale to gain a complete understanding of the factors affecting selection.

Factors affecting habitat selection by a small spawning charr population, bull trout, Salvelinus confluentus: implications for recovery of an endangered species

AbstractBull trout, Salvelinus confluentus (Suckley), populations are declining in many streams of North America and are listed under the Endangered Species Act in the United States. Many small populations are isolated in fragmented habitats where spawning conditions and success are not well understood. Factors affecting habitats selected for redds by spawning bull trout and redd habitat characteristics within Gold Creek, a headwater stream in the Yakima River within the Columbia River basin, Washington State, USA, were evaluated. Most spawning (>80% of the redds) occurred in upstream habitats after dewatering of downstream channels isolated fish. Habitats were selected or avoided in proportions different to their availability. For example, most bull trout selected pools and glides and avoided riffles despite the latter being more readily available. Although preferences suggest influences of prolonged fish entrapment, site fidelity could be important. A habitat with redds commonly contained abundant cover, gravel substratum and higher stream flows. The major factors influencing habitat selection by spawning fish and their persistence in streams of the Yakima and Columbia River regions include entrapment of fish by dewatering of channels and geographical isolation by dams. The goal of the US Government's recovery plan is ‘to ensure the long‐term persistence of self‐sustaining bull trout populations’. Recovery plans linked to provisions for protecting and conserving bull trout populations and their habitats were recommended. Landscape approaches are needed that provide networks of refuge habitats and greater connectivity between populations. Concurrent recovery efforts are encouraged to focus on protecting small populations and minimizing dangers of hybridization.

Shifts in habitat associations of dung beetles in northern Spain: Climate change implications

:We examined whether dung beetle species shift their habitat associations (vegetation types) with different climatic conditions, using altitudinal and seasonal gradients as analogues of future climate change scenarios. Dung beetle assemblages in Picos de Europa (northern Spain) were monitored by dung-baited pitfall trapping in three vegetation types (woodland, heathland, and pasture), three altitudinal zones (520-600 m, 950-963 m, and 1,230-1,275 m) and during two different seasons (summer and autumn) in 1994. Most species shifted their habitat use on the altitudinal and seasonal gradient in response to changes in microclimatic conditions (temperature). They were generally associated with heathland and woodland (shaded habitats) at lower altitudes, but they were increasingly associated with pastures (open habitat) as altitude increased. There was also a greater association with pastures in the coldest season (autumn) and with heathland and woodland in the warmest season (summer). These results suggest that climate change could be a major factor influencing habitat selection in dung beetles. The magnitude of habitat shifts was species specific, so climate warming also has the potential to generate new or different species interactions. The research presented here supports the feasibility of using microclimatic gradients within a region to study the potential effects of future climate change on both species and communities.

Habitat‐specific behavioural thermoregulation by black rat snakes (Elaphe obsoleta obsoleta)

Thermoregulation is thought to be the most important factor influencing habitat selection by terrestrial ectotherms, at least in temperate climates. The cost‐benefit model of thermoregulation predicts that ectotherms should invest more in thermoregulation when the costs of doing so are low (when the thermal quality of the habitat is high). However, the extent to which ectotherms vary their thermoregulatory behaviour according to the thermal quality of habitats is currently unknown. We studied the relationship between habitat use and thermoregulation in 53 black rat snakes using temperature‐sensitive radio‐transmitters. Among the habitats available to black rat snakes, edges had the highest thermal quality, retreat sites and forest were intermediate, and open habitats had the lowest thermal quality. Black rat snakes experienced more favourable body temperatures while in barns (retreat sites) than in edges, and in edges than in forest. During the day, the effectiveness and the extent of thermoregulation by the snakes were equal in barns and forest, but much lower in edges. In fact, black rat snakes selected thermally favourable microhabitats less than their availability while in edges. Therefore, more favourable body temperatures were not necessarily achieved in thermally superior habitats by increased thermoregulation, but simply because favourable temperatures were encountered more often in those habitats. This result is contrary to the central prediction of the cost‐benefit model of thermoregulation and we suggest that this model should be modified to put more emphasis on other costs of thermoregulation, such as increased predation risk or lost foraging opportunities.

Biotic influences on habitat selection by young-of-year walleye (Stizostedion vitreum) in the demersal stage

The influence of prey availability and predation risk on the distribution of young-of-year (YOY) walleye (Stizostedion vitreum) was investigated by comparing species associations with the relative abundance of YOY walleye across nine habitat types using an underwater visual assessment technique. During the early demersal period (mid-June to mid-July), YOY walleye were found primarily in areas of high macrophyte cover at 2–5 m depth. YOY walleye abundance was positively correlated with the abundance of prey fishes at this time. YOY walleye shifted to low-cover, shallow areas during the late demersal period (mid-July to late August), and the significant prey associations disappeared. Although the selected habitats are considered to have low predation risk, the distribution of YOY walleye was not related to our index of predator abundance in either time period. YOY walleye were not observed in three of the nine habitat types, suggesting that active habitat selection was occurring. High macrophyte cover and prey availability appear to be the major factors influencing habitat selection during the early demersal period. Although our results do not demonstrate the functional significance of the shift of YOY walleye into shallow water, we hypothesize that these habitats are selected as refugia from particular predators such as adult walleye.

Biotic influences on habitat selection by young-of-year walleye (<i>Stizostedion vitreum</i>) in the demersal stage

The influence of prey availability and predation risk on the distribution of young-of-year (YOY) walleye (Stizostedion vitreum) was investigated by comparing species associations with the relative abundance of YOY walleye across nine habitat types using an underwater visual assessment technique. During the early demersal period (mid-June to mid-July), YOY walleye were found primarily in areas of high macrophyte cover at 2–5 m depth. YOY walleye abundance was positively correlated with the abundance of prey fishes at this time. YOY walleye shifted to low-cover, shallow areas during the late demersal period (mid-July to late August), and the significant prey associations disappeared. Although the selected habitats are considered to have low predation risk, the distribution of YOY walleye was not related to our index of predator abundance in either time period. YOY walleye were not observed in three of the nine habitat types, suggesting that active habitat selection was occurring. High macrophyte cover and prey availability appear to be the major factors influencing habitat selection during the early demersal period. Although our results do not demonstrate the functional significance of the shift of YOY walleye into shallow water, we hypothesize that these habitats are selected as refugia from particular predators such as adult walleye.

Factors affecting habitat use by mule deer (Odocoileus hemionus) in the central part of the Chihuahuan Desert, Mexico: an assessment with univariate and multivariate methods

Habitat use by mule deer was studied in the Mapimí Biosphere Reserve in the Chihuahuan Desert, Mexico. The deer population in this area is distributed among isolated hills and sierra. Because of their similar soil and vegetation characteristics, these hills are a homogeneous element of the landscape. This study was carried out within this element, in order to understand the habitat variables that are important for deer in the selection of habitat. Univariate as well as multivariate analytical methods were used in a complementary fashion to identify habitat variables associated with habitat selection during wet and dry seasons. The univariate method detected a relationship between habitat use and variation in slope (measurements of unevenness in terrain), in both seasons, it also detected a relationship between habitat use and the distance to water in the dry season. The multivariate method detected higher use of sites with greater unevenness in the terrain, higher shrub diversity, greater visibility and that were closer to water sources. Unevenness in terrain seems to be the most important factor influencing habitat selection by mule deer. This factor is limited to isolated hills and sierra in this part of the Chihuahuan Desert, so it is a spatially well defined resource. Such areas should be considered as a high-priority for the conservation of this species.

Ovipositional Stimuli of Angoumois Grain Moth (Lepidoptera: Gelechiidae), a Primary Pest of Stored Grains

Ovipositional preferences of Sitotroga cerealella (Olivier) were measured in the laboratory to characterize the stimuli eliciting oviposition in this widespread pest of stored grains. Substrates used for oviposition included grains presenting both physical and chemical stimuli as well as surrogates presenting only physical stimuli. Chemical factors associated with grains stimulated oviposition, but physical stimuli, primarily the presence of crevices, were of much greater importance. Moths reared for approximately 15 generations in the laboratory were less sensitive to grain factors than were moths more recently collected from the field. Experiments with surrogrates presenting a precisely defined range of crevice sizes confirmed that ovipositional response increased as crevice size narrowed. The results suggest that factors influencing habitat selection are probably very important in this insect because of indiscriminate oviposition on substrates that present appropriate physical stimuli but are entirely unsuitable for larval consumption.