Irruptive Migration of Chestnut-Backed Chickadees to Southwestern Idaho

I document irruptive movements of the Chestnut-backed Chickadee to Lucky Peak in southwestern Idaho, over 80 km from its regular range. Chestnut-backed Chickadees were captured and/or observed at Lucky Peak in 2000, 2004, and 2008. To evaluate the context for this phenomenon, I also examined data on capture of all chickadees and other irruptive species at Lucky Peak and numbers of irruptive species recorded on Idaho Christmas Bird Counts (CBC) from 1997 to 2011. Though CBCs in the winter of 2004–05 (following the largest movement of Chestnut-backed Chickadees at Lucky Peak in fall 2004) found high numbers of many irruptive species, relatively low numbers of Chestnut-backed Chickadees were detected on Idaho CBCs that winter. Overall, I observed little correspondence between capture totals at Lucky Peak and Idaho CBC data for potentially irruptive species in general, and little correspondence between years with Chestnut-backed Chickadees and patterns of any irruptive species in CBC data for the the subsequent winter. The seasonal movement patterns of this species, their regularity, and their causes warrant greater attention

Towards the Establishment of Landbird Migration Monitoring Networks in the United States

Migration monitoring of landbirds, in its various forms, is a well-established research endeavor across much of North America. While monitoring efforts at individual sites have contributed much to our knowledge of the biology of migrants, these studies have limited potential for population monitoring and for addressing certain broader questions about migrants. Meanwhile, there is still much to be learned about the habitat use, conservation needs, population trends, demographics, and general stopover ecology of migrants. As a model for migration monitoring networks, the establishment and operation of monitoring and research networks for other purposes in avian research has met with much success. We suggest that the involvement of many monitoring sites in a larger network can provide unique and necessary research, conservation, and monitoring opportunities for the study of birds during migration. While many are willing and eager to participate in such networks, the critical issue has been the ability of institutions to afford personnel to coordinate them. Here we review historical and present networks devoted to avian research and consider applications to the development of migration monitoring networks in the Americas

Stopover Ecology of Autumn Landbird Migrants in the Boise Foothills of Southwestern Idaho

The topography of western North America provides a complex landscape for landbird migrants, and stopover patterns in this region are poorly understood. We examined seven years of stopover data (1997–2003) from a montane area in southwestern Idaho to determine whether this area provides suitable stopover habitat. We compared the proportion of birds recaptured, stopover duration, and changes in energetic condition within and among species and between two mist-netting sites located in different habitats. The proportion of birds recaptured ranged from zero to over 20%, and fewer than 5% of individuals were recaptured in most species. Mean minimum stopover durations from recapture data ranged from 1 to 10 days; most species averaged less than 6 days. Stopover duration estimates from open-population models were comparable but generally greater than estimates from recapture data. As found in stopover studies from other regions, stopover metrics varied within and among species in Idaho. However, most migrants in this study exhibited an ability to gain mass, evidenced both by recapture data and by regression of energetic condition against time since sunrise. These data imply that montane habitats in Idaho are suitable stopover sites. It follows that these habitats might serve an important role for many landbird migrants during the period of late summer molt and autumn migration, a time when many lowland areas of the West, including some riparian systems, are especially arid. We suggest that including montane nonriparian habitats in future stopover ecology studies will allow for a more complete understanding of migrant habitat needs in the West

Effects of Regional Cold Fronts and Localized Weather Phenomena on Autumn Migration of Raptors and Landbirds in Southwest Idaho

Weather has a significant effect on avian migration, but whether the influence is similar across diverse geographic regions and across all species remains to be determined. We evaluated the effect of regional cold fronts and localized weather phenomena on the timing of autumn migration of multiple species of landbirds and raptors in southwest Idaho. The focus of the analysis was on total landbirds and the ten most common landbird species, along with total raptors and the eight most common raptor species. Using 13 years of data from the Idaho Bird Observatory in southwest Idaho (1997–2009), including standardized mist-net captures of landbirds and counts of raptors during autumn migration, we determined significant patterns that advance our understanding of the variables influencing avian migration in the West. Our data show a depression of numbers of most migratory species on the days immediately before, during, and after the passage of a cold front, with peak flights of most species occurring several days prior to or after cold fronts. This pattern was further substantiated by a detailed analysis of many weather variables illustrating that the majority of species choose to migrate during calmer winds, high pressure, and between cold fronts when the opportunity presents itself. In the Intermountain West, cold fronts are fewer in fall than in much of the rest of North America, so migrants may have greater choice of conditions under which to migrate and this behavior may be more common

Molt Strategies and Age Differences in Migration Timing Among Autumn Landbird Migrants in Southwestern Idaho

Intraspecific patterns of autumn migration timing are not well known, particularly in the western United States. Here, we (1) describe autumn migration timing and age ratios of landbird migrants in southwestern Idaho, (2) examine differences in timing among age and sex classes, and (3) demonstrate how prebasic molt strategies affect migration timing differences between age classes. As a group, Neotropical migrants were most common from late July through early September, whereas temperate migrants were most common from mid-September into early October. Proportion of hatch-year birds was 74.5% for all migrants combined and ranged from 33.3% to 100% for individual species. Timing differences between sex classes were detected in only a few species and no general patterns emerged. In 22 of 31 Neotropical and temperate migrants examined, there were significant differences in timing between adults and hatch-year birds. In species in which adults begin fall migration before replacing flight feathers, adults migrated earlier than hatch-year birds. Conversely, in species in which adults molt flight feathers on or near the breeding grounds before departing on fall migration, hatch-year birds migrated earlier than adults in all but one case. Therefore, it appears that molt strategy is a powerful determinant of intraspecific migration timing differences and, to our knowledge, this is the first study to document this pattern among migrant passerines of North America

Species Richness and Nesting Success of Migrant Forest Birds in Natural River Corridors and Anthropogenic Woodlands in Southeastern South Dakota

Forest fragmentation is thought to be partially responsible for declines in many Neotropical migrant birds due to the combined effects of higher rates of brood parasitism and increased predation near forest edges. A majority of the forested habitat in the northern prairie region is found in riparian corridors, but this native habitat has been much reduced from its historical extent. However, additional woodland nesting habitat has been established within the last century in the form of isolated woodlots on farms. We compared abundance, species richness, and nesting success of migrant forest birds breeding in native riparian corridors and anthropogenic woodlots. The two habitats had similar bird abundances but native riparian woodlands were more species-rich than woodlots. We located a total of 650 nests, with 320 nests of 15 species in woodlots and 331 nests of 25 species in riparian corridors. Nesting success was not significantly different between the two habitats for all species combined or for individual species with ≥15 nests in each habitat. Nests above 5 m were more successful than lower nests, but distance to woodland edge did not influence nesting success. Nests initiated in the middle and late portions of the nesting season were more successful than early season nests, significantly so in woodlots. Thus, anthropogenic woodlots were as suitable as natural habitats for successful nesting. However, many of the Neotropical migrants occurring in riparian habitats were absent from woodlots, which suggests that riparian corridors are especially important habitats for breeding birds in the northern prairie region

Effects of Prey Abundance on Breeding Season Diet of Northern Goshawks (\u3cem\u3eAccipiter gentilis\u3c/em\u3e) Within an Unusual Prey Landscape

A critical element of diet analysis is species adaptability to alternative prey sources. The breeding-season diet of Northern Goshawks (Accipiter gentilis) includes both mammalian and avian species, varies geographically, and is often dependent upon tree squirrels of the genera Sciurus andTamiasciurus. We studied alternative prey sources of Northern Goshawks in the South Hills of south-central Idaho, an area where tree squirrels are naturally absent and other prey frequently important in the diet of goshawks, such as smaller corvids, are uncommon. We quantified the diet of goshawks using nest cameras and surveyed abundance of prey using line transects. We found that goshawks consumed roughly 18.5% birds and 78.7% mammals by biomass, with diet dominated by the Belding\u27s ground squirrel (Urocitellus beldingi, also known as Spermophilus beldingi; 74.8% of total biomass consumed); however, the percentages of mammals and birds in the diet varied between years. The diet was low in diversity, with high overlap among nests, indicating a strong local dependence on the dominant food item. Lastly, the proportion of mammalian prey in the diet was greater in larger broods than in smaller broods. This study provides new insight into the adaptability of the goshawk, particularly in areas with unique prey assemblages

Montana's IMBCR Program: Utility of Seven Years of Statewide Landbird Monitoring Data

The 2016 field season marks the 7th consecutive year of statewide implementation of the Integrated Monitoring in Bird Conservation Regions program (IMBCR) for monitoring bird populations in the state of Montana.  Using a spatially-balanced, hierarchical study design, the IMBCR program provides density and occupancy estimates for bird species at various geographic extents (strata) across the western U.S.  Based largely on agency investment, primary sampling occurs in all USFS R1 National Forests and extensive grassland/sagebrush habitats on Montana BLM lands statewide.  Significant sampling also occurs in various habitats on private lands.  Using these data, as well as tools available on the Rocky Mountain Avian Data Center web console, agencies and NGO partners can evaluate avian distribution and population dynamics statewide.  As an effective monitoring program, the IMBCR program informs research questions, landscape-level management and conservation action.  The design and current applications of the IMBCR program are summarized

Habitat Associations, Relative Abundance, and Species Richness of Autumn Landbird Migrants in Southwestern Idaho

We used count surveys and mist-net captures to compare habitat associations, relative abundance, species richness, and community similarity of migrant landbirds among four major habitats in the Boise Foothills of southwestern Idaho. Count surveys were conducted from August through October 1997–2000 in conifer forest, mountain shrubland, shrubsteppe, and riparian shrubland. We compared bird detections among habitats for all birds pooled, individual species, and three migration strategies: Neotropical, temperate, and resident (including irruptive migrants). Mountain shrubland supported the highest numbers of temperate migrants; both mountain shrubland and riparian shrubland had the highest numbers of Neotropical migrants; and conifer forest had the highest numbers of residents. Species richness was highest in riparian shrubland and lowest in shrubsteppe, whereas diversity and evenness were highest in conifer forest and mountain shrubland. Mist netting was conducted from mid-July to mid-October in two habitats: mountain shrubland (1997– 2002) and riparian shrubland (1998–1999). Captures (adjusted for effort) were compared among habitats in 1998–1999 and were similar for temperate migrants, whereas mountain shrubland had higher abundance of Neotropical migrants and riparian shrubland had higher abundance of irruptive migrants. Richness, diversity, and evenness were similar and there was high community similarity between mountain shrub and riparian shrubland habitats. These results emphasize the importance of montane habitats, especially deciduous shrub communities, to migrants in the Intermountain West

Predicting Nesting Habitat of Northern Goshawks in Mixed Aspen-Lodgepole Pine Forests in a High-Elevation Shrub-Steppe Dominated Landscape

We developed a habitat suitability model for predicting nest locations of breeding Northern Goshawks (Accipiter gentilis) in the high-elevation mixed forest and shrub-steppe habitat of south-central Idaho, USA. We used elevation, slope, aspect, ruggedness, distance-to-water, canopy cover, and individual bands of Landsat imagery as predictors for known nest locations with logistic regression. We found goshawks prefer to nest in gently-sloping, east-facing, non-rugged areas of dense aspen and lodgepole pine forests with low reflectance in green (0.53 - 0.61 μm) wavelengths during the breeding season. We used the model results to classify our 43,169 hectare study area into nesting suitability categories: well suited (8.8%), marginally suited (5.1%), and poorly suited (86.1%). We evaluated our model’s performance by comparing the modeled results to a set of GPS locations of known nests (n = 15) that were not used to develop the model. Observed nest locations matched model results 93.3% of the time for well suited habitat and fell within poorly suited areas only 6.7% of the time. Our method improves on goshawk nesting models developed previously by others and may be applicable for surveying goshawks in adjacent mountain ranges across the northern Great Basin