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The forage maturation hypothesis (FMH) states that energy intake for ungulates is maximised when forage biomass is at intermediate levels. Nevertheless, metabolic allometry and different digestive systems suggest that resource selection should vary across ungulate species. By combining GPS relocations with remotely sensed data on forage characteristics and surface water, we quantified the effect of body size and digestive system in determining movements of 30 populations of hindgut fermenters (equids) and ruminants across biomes. Selection for intermediate forage biomass was negatively related to body size, regardless of digestive system. Selection for proximity to surface water was stronger for equids relative to ruminants, regardless of body size. To be more generalisable, we suggest that the FMH explicitly incorporate contingencies in body size and digestive system, with small‐bodied ruminants selecting more strongly for potential energy intake, and hindgut fermenters selecting more strongly for surface water.

Feral burros (Equus asinus) and horses (E. ferus caballus) inhabiting public land in the western United States are intended to be managed at population levels established to promote a thriving, natural ecological balance. Double‐observer sightability (MDS) models, which use detection records from multiple observers and sighting covariates, perform well for estimating feral horse abundances, but their effectiveness for use in burro populations is less understood. These MDS models help minimize detection bias, yet bias can be further reduced with models that account for unmodeled variation, or residual heterogeneity, in detection probability. In populations containing radio‐marked individuals, residual heterogeneity can be estimated with MDS models by including a covariate that corresponds to the marked status of a group (MH models). Another approach is to use information from detections missed by both observers to account for the characteristics that make groups more or less likely to be detected, or recaptured, by the second observer (MR models). We used aerial survey data from 3 burro populations (Sinbad Herd Management Area, UT [2016–2018], Lake Pleasant Herd Management Area, AZ [2017], and Fort Irwin National Training Center, CA [2016–2017]) to develop MDS models applicable for feral burros in the southwestern United States. Our objectives were to quantify precision and bias of standard MDS surveys for feral burros and to examine which model type for incorporating residual heterogeneity (MH or MR) would result in the least‐biased estimates of burro populations relative to the minimum number known alive (MNKA) within the Sinbad Herd Management Area. Standard MDS model estimates achieved a mean coefficient of variation of 0.08, while underestimating MNKA by an average of 27.1%. Accounting for residual heterogeneity through recapture probability in MR models resulted in estimates closer to MNKA than MH models (9.5% vs. 16.5% less than MNKA). Our results indicate that MDS models can achieve precise enough estimates to monitor feral burro populations, but they routinely produce negatively biased estimates. We encourage the use of radio‐collars to reduce bias in future burro surveys by accounting for residual heterogeneity through MR models.

Imperiled species recovery is a high‐stakes endeavor where uncertainty surrounding effectiveness of conservation actions can be an impediment to implementation at necessary scales, especially where habitat restoration is required. Gunnison sage‐grouse (Centrocercus minimus) represents one such species in need of large‐scale habitat restoration. It is a federally threatened sagebrush (Artemisia spp.) obligate bird with a limited range in Colorado and Utah. Threats to recovery of Gunnison sage‐grouse include conifer expansion into sagebrush along with additional habitat loss and degradation attributed to human development and agricultural conversion. Recovery of Gunnison sage‐grouse and other sensitive species can be aided by spatial tools that forecast plausible outcomes of conservation actions. We illustrate this by using a novel framework for predicting outcomes of proactive tree removal and subsequent sagebrush restoration for the Gunnison sage‐grouse. To assess threats on Gunnison sage‐grouse lek presence, we developed a spatially explicit breeding habitat model to compare active lek and random pseudo‐absence locations from 2015. Models identified land cover, climatic, and abiotic variables at landscape‐level scales (0.56 and 4 km) most important for predicting breeding habitat. Our model correctly differentiated between lek and pseudo‐absence locations 94% of the time. All but one of the active leks (n = 94) were in areas with >0.65 probability of lek occurrence. Using this probability value as a threshold, we predicted 15% of the current grouse range as high‐quality breeding habitat. Simulated removal of trees in areas with ≤30% tree canopy cover (0.56‐km scale) increased extent of high‐quality habitat fourfold (59%). Hypothetical restoration of sagebrush cover in the same areas increased habitat quality an additional 11%. Our breeding habitat model indicated that targeted tree removal and sagebrush restoration have potential to improve Gunnison sage‐grouse breeding habitat. While our habitat treatment scenarios were not meant to be prescriptive, they highlight that considerable uplift in Gunnison sage‐grouse breeding habitat may be possible across much of its range with cooperation from multiple stakeholders and illustrates the utility of this approach for predicting biological return on investment.

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Probability-based sampling designs for aerial surveys are useful for estimating wintering waterfowl abundances in large areas with contiguous habitat (e.g., Mississippi Alluvial Valley). The effectiveness of these approaches for estimating abundance of nonbreeding waterfowl in small areas with discontinuous habitat has rarely been assessed. Surveys conducted within riverine areas introduce sampling design difficulties because of discontinuous bottomland habitat and irregularity of flooding events. Therefore, we implemented and evaluated a generalizable grid-based, stratified random sampling design to estimate weekly duck abundance within the Wabash River floodplain in southeastern Illinois and southwestern Indiana, USA, during midwinter and early spring 2012 and 2013. We used aerial and ground-based counts to generate abundance estimates and evaluate within-week variation of counts. Peak duck abundance totaled 279,717 (SE ¼ 69,101) in 2012 and 742,027 (SE ¼ 296,563) in 2013. Dabbling ducks were the most abundant duck guild detected and abundance estimates for this group met our precision goal (CV 0.25) in 4 of 18 surveys ( x ¼ 0.33, range ¼ 0.20-0.51). We compared the grid-based approach with a traditional aerial inventory and found that estimates from the grid-based approach were on average 75,175 (SE ¼ 46,768) greater than inventory counts. Desired levels of precision were often not met, yet design improvements in 2013 notably increased precision, suggesting that further modifications may allow this method to be useful in riverine areas with discontinuous and ephemeral habitat. Ó 2017 The Wildlife Society.

Feral horse (Equus ferus caballus) populations on public rangelands in the western United States threaten forage production for livestock and wildlife habitat. Interference competition between feral horses and heterospecifics at watering sources can have negative effects on livestock and wildlife. Researchers have documented altered timing and behavior of wild ungulates at water sources when horses were present. The few studies examining these interactions have infrequently occurred within areas specifically managed for feral equids and have not occurred in sites with cattle. We used motion-sensitive cameras at 8 watering sources to document watering activity patterns and construct indices of temporal overlap among feral horses, cattle, elk (Cervus canadensis), mule deer (Odocoileus hemionus), and pronghorn (Antilocapra americana) within the Adobe Town Herd Management Area in southern Wyoming, USA, between June and September 2018 and 2019. Feral horses, cattle, and pronghorn exhibited a high degree of temporal overlap (>79%) in water use, with feral horses and pronghorn exhibiting the highest estimated percent overlap (88.1%, 95% CI = 86.5-89.6%). Mule deer and elk watering activity also overlapped with horses and cattle but to a lesser degree (<55%). Feral horses spent a mean of 16.7 ± 30.5 (SD) minutes during a watering event and were present at a given water source on average 4.5 ± 6.3% and up to 34.9% of the day, which is less than reported in previous studies. Cattle spent on average 23.5 ± 44.9 minutes during a watering event, and were present on average 4.2 ± 7.7% and up to 42.4% of the day at a single water source. Results of generalized linear mixed-effects models indicated that number of conspecifics was the strongest predictor of visit duration for pronghorn and horses; hour of the day and group size of heterospecifics were informative, but less important, variables. There was no difference in peak visitation time for any species between sites of high versus low horse or cattle use. Despite temporal overlap, we did not find evidence of interference competition between feral horses, cattle, and pronghorn. We recommend future examination of interference competition and its biological consequences between introduced and native ungulates at water sources of varying size across sites, equid population levels, and livestock stocking rates.

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