Western burrowing owls (Athene cunicularia hypugaea) are endangered in Canada and several western U.S. states. Population declines have been linked with control measures aimed at burrowing mammals and loss of nesting habitat. The owls frequently associate with irrigated agriculture throughout portions of their western U.S. range. To determine potential factors driving the association of burrowing owls with agriculture, we examined availability of suitable nest burrows (burrow availability hypothesis), abundance of potential prey (prey availability hypothesis), and predation of nest burrows (predation hypothesis) for owls nesting in the Snake River Birds of Prey National Conservation Area in southwestern Idaho during 2001–2002. Nest burrow availability did not differ between agricultural and nonagricultural habitats, and occupancy rates of owls in artificial burrows were greater near agriculture. More rodent prey species were live‐trapped in agricultural habitat compared with nonagricultural habitat, and there was no difference in relative abundance of prey between habitat types. Pellet remains indicated greater abundance and biomass of prey being consumed in agricultural habitat compared with nonagricultural habitat. Finally, predation rates of dummy nests in agricultural and nonagricultural habitat did not differ. These findings allow us to reject the burrow availability and predation hypotheses, while the prey availability hypothesis remains tenable. Thus, burrowing owls may nest near irrigated agriculture in southwestern Idaho because of increased diversity or availability of prey. We suggest that research is needed to determine how widespread this prey availability relationship may be and how management of burrowing owls in agricultural landscapes may take advantage of this apparent rich prey resource.
ABSTRACT. The Short-eared Owl (Asio flammeus) is an open-country species breeding in the northern United States and Canada, and has likely experienced a long-term, range-wide, and substantial decline. However, the cause and magnitude of the decline is not well understood. We set forth to address the first two of six previously proposed conservation priorities to be addressed for this species:(1) better define habitat use and (2) improve population monitoring. We recruited 131 volunteers to survey over 6.2 million ha within the state of Idaho for Short-eared Owls during the 2015 breeding season. We surveyed 75 transects, 71 of which were surveyed twice, and detected Short-eared Owls on 27 transects. We performed multiscale occupancy modeling to identify habitat associations, and performed multiscale abundance modeling to generate a state-wide population estimate. Our results suggest that within the state of Idaho, Short-eared Owls are more often found in areas with marshland or riparian habitat or areas with greater amounts of sagebrush habitat at the 1750 ha transect scale. At the 50 ha point scale, Short-eared Owls tend to associate positively with fallow and bare dirt agricultural land and negatively with grassland. Cropland was not chosen at the broader transect scale suggesting that Short-eared Owls may prefer more heterogeneous landscapes. On the surface our results may seem contradictory to the presumed land use by a "grassland" species; however, the grasslands of the Intermountain West, consisting largely of invasive cheatgrass (Bromus tectorum), lack the complex structure shown to be preferred by these owls. We suggest the local adaptation to agriculture represents the next best habitat to their historical native habitat preferences. Regardless, we have confirmed regional differences that should be considered in conservation planning for this species. Last, our results demonstrate the feasibility, efficiency, and effectiveness of utilizing public participation in scientific research to achieve a robust sampling methodology across the broad geography of the Intermountain West.Recensement de Hiboux des marais (Asio flammeus) dans la région Intramontagnarde Ouest nordaméricaine : utilisation de la participation citoyenne pour effectuer un suivi à grande échelle RÉSUMÉ. Le Hibou des marais (Asio flammeus), espèce de milieux ouverts nichant dans le nord des États-Unis et au Canada, a vraisemblablement subi une baisse importante de longue date et à grande échelle. Toutefois, la cause et la magnitude de cette baisse ne sont pas bien comprises. Nous avons choisi d'étudier les deux premières de six priorités de conservation proposées antérieurement pour cette espèce : 1) mieux établir l'utilisation de l'habitat; et 2) améliorer le suivi de la population. Nous avons recruté 131 bénévoles pour inventorier plus de 6,2 millions d'ha dans l'État de l'Idaho durant la saison de nidification 2015 du Hibou des marais. Nous avons inventorié 75 transects, dont 71 à deux reprises, et avons détecté le Hibou des marais dans 27...
The Short-eared Owl (Asio flammeus) is a species of conservation concern in the western USA, with evidence for declining population sizes. Monitoring of Short-eared Owls is complicated because of their low site fidelity and nomadic movements. We recruited community-science participants to implement a multi-year survey of Short-eared Owls across eight states in the western USA, resulting in a program of sufficient temporal and spatial dimensions to overcome many of the challenges in monitoring this species. We implemented both multi-scale occupancy and colonization/extinction modeling to provide insights into land-cover use, and to identify which cover types supported higher occurrence. Short-eared Owls were associated with native and anthropogenic land-cover types, but site occupancy varied among these categories and at different scales. Native grasslands, marsh/riparian, hay/fallow agriculture, and cultivated croplands were occupied most consistently across years. Occupancy rates differed at different scales (e.g., marsh/riparian was the only land-cover type positively associated with occupancy at both transect and point scales). Contrary to expectations, native shrubland was negatively associated with occupancy at the point scale, and exhibited low colonization and high extinction rates. Our results suggest that conserving native landscapes in general, and grasslands, marsh, and riparian areas specifically, would benefit Short-eared Owls. Furthermore, Short-eared Owl occupancy was positively associated with hay/fallow land-cover types, suggesting that some nonnative land-cover types can function as Short-eared Owl habitat. Lastly, our results highlight how developing a broad-scale community science survey can inform conservation for a species not well monitored by existing survey programs.
For a colonial‐nesting bird, like the white‐faced ibis (Plegadis chihi), the landscape surrounding the breeding colony can be important. White‐faced ibis must rely on areas outside their breeding colony for foraging, but this part of their life history has received little attention, and the management of this landscape even less so. To address this knowledge gap, we conducted road‐based driving surveys and a randomly selected, spatially balanced sample survey of agricultural fields within a 22‐km radius of the 2 largest white‐faced ibis breeding colonies in Idaho, USA: Market Lake Wildlife Management Area and Mud Lake Wildlife Management Area. Our study took place in 2012 and the primary objective was to quantify patterns of foraging habitat use of this marsh‐nesting species, particularly associations with specific irrigation practices and crop types. We documented the majority of foraging birds in flood‐irrigated and wheel‐line sprinkler‐irrigated agricultural fields (76%) and natural wetlands (13%), which were limited in our study area (3% of land cover). Even though 70% of the agricultural landscape included center pivot sprinkler irrigation, only 11% of foraging observations came from this irrigation type. Most agricultural fields (>85%) used by foraging ibis were flood‐irrigated and all had standing water or recent moisture at the time of use. Though ibis used many crop types when foraging in flooded agricultural fields, ibis use of alfalfa (58%) was greater than availability (38%). We also observed distinct distribution patterns around the 2 breeding colonies. Whereas birds foraged in all directions around Mud Lake (~80%) within a 12‐km radius from the colony, we observed over half of birds around Market Lake foraging within 12–22 km, and almost exclusively to the south and southeast of the colony, reflecting the distribution of flood‐irrigated agriculture in the area. The most common foraging distance (12–22 km) around Market Lake is greater than found in existing literature, suggesting that the foraging habitat is limited within 12 km of the colony and that the birds may need to travel farther to find adequate foraging habitat. Flood‐irrigated agriculture and natural wetlands provide foraging habitats for white‐faced ibis in eastern Idaho and should be considered in future management and conservation of wetland birds.
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