Frank R. Thompson

Landscape And Edge Effects On The Distribution Of Mammalian Predators In Missouri

Raccoons (Procyon lotor), opossums (Didelphis virginiana), and striped skunks (Mephitis mephitis) are predators of forest songbird eggs and nestlings. We examined the relative abundance of these predators at landscape and local scales to better understand predation risks. At the landscape scale, we examined the relationship between detection rates of raccoons, opossums, and striped skunks on 25 scent-station routes distributed across Missouri and surrounding landscape characteristics. Raccoon abundance was related to latitude, stream density, and mean patch size of agricultural lands. Opossum abundance was related to stream density, contagion, mean nearest-neighbor distance between forest patches, and latitude. Striped skunk abundance was not related to landscape characteristics we examined. At a local scale, we used sooted-plate scent stations to compare the relative abundance of raccoon and opossums in forest interiors to forests adjacent to agricultural fields, roads, clearcuts, and streams. Raccoons were more abundant in forest edges adjacent to agricultural fields and streams. Opossum abundance varied greatly among years and there was no consistent edge effect on abundance. Local features such as proximity to some types of edge as well as large-scale factors such as landscape patterns in land use may affect predator abundance and potentially sonngbird-nest predation rates.

Video identification of predators at songbird nests in old fields

That we always clearly detected a small dose of dyed sugar solution in the color of feces of hand-fed chicks, and that we failed to detect any color changes in chick fecal sacs during our feeder presentation, suggest hat parent sunbirds feed none or only negligible amounts of feeder sugar solution to their chicks. Moreover, no detectable amounts of sugar occurred in nestling esophagi or excreta fluid samples, despite the fact that we could simulate such a measurable effect through hand-feeding chicks with nectar. Therefore, we conclude that nectar is an exclusively parental food type in Orange-tufted Sunbirds. It has been suggested that hummingbirds feed nectar to their chicks (Hainsworth 1977). To our knowledge, however, no one has documented this empirically. Therefore, we suggest that our methodology can be used to determine whether adult hummingbirds feed nectar to their nestlings. Acknowledgments.--This study was funded by a grant from the Mitrani Center for Desert Ecology and is paper number 258 of the Mitrani Center.

Forest bird response to regeneration practices in central hardwood forests

We studied breeding songbird populations in a managed, predominantly forested landscape, in southeastern Missouri. We determined differences in the relative abundance of breeding birds in forest stands that had been harvested by the clearcut (n = 12), shelterwood (n = 12), group selection (n = 12), and singletree selection (n = 10) forest regeneration methods, and mature even-aged stands (n = 12). Five migrant songbirds, the blue-winged warbler (Vermivora pinus), prairie warbler (Dendroica discolor), rufous-sided towhee (Pipilo erythrophthalmus), white-eyed vireo (Vireo griseus), and yellow-breasted chat (Icteria virens), were more abundant in clearcut treatments than other treatments (P 0.30). Nest success of species nesting in clearcut and shelterwood treatments was 18-50%. The percent of the site in gaps, shrub stem density, and tree-diameter distribution differed among forest regeneration methods (P < 0.001). We believe habitat requirements of birds in managed forests can be best met by a mixture of evenand uneven-aged forest management that creates a range of disturbance sizes. J. WILDL. MANAGE. 61(1):159-171

POSTFLEDGING DISPERSAL, HABITAT USE, AND HOME-RANGE SIZE OF JUVENILE WOOD THRUSHES

Although the availability of suitable postfledging habitat potentially is piv- otal to juvenile Neotropical migratory birds, data on dispersal, habitat use, and home-range size are limited. We used radio telemetry to study the postfledging ecology of juvenile Wood Thrushes (Hylocichla mustelina) in the Ozark Mountains of southern Missouri. Natal home ranges were in mature oak-hickory forest, and natal home-range size ranged from 2.6 to 24.8 ha. Juveniles dispersed independently from their natal home ranges to post-dispersal ranges, with a mean dispersal direction of 185.2 + SD of 77.20 and a mean distance of 2.08 ? 1.48 km. Habitats used after dispersal differed from natal habitats and included early succes- sional oak-hickory and pine forests, mid-successional pine forest, mature riparian forest, and forest/field edges. These habitats were characterized by a dense understory and thick ground cover. Post-dispersal home-range size averaged 1.53 ha. Our data suggest that in large tracts of mature deciduous forest, a mosaic of early and mid-successional forest stands, along with mature riparian forest, will accommodate both the breeding and post-dispersal habitat requirements of Wood Thrushes and other Neotropical migratory birds. Received 21

Conserving migratory land birds in the New World: Do we know enough?

Migratory bird needs must be met during four phases of the year: breeding season, fall migration, wintering, and spring migration; thus, management may be needed during all four phases. The bulk of research and management has focused on the breeding season, although several issues remain unsettled, including the spatial extent of habitat influences on fitness and the importance of habitat on the breeding grounds used after breeding. Although detailed investigations have shed light on the ecology and population dynamics of a few avian species, knowledge is sketchy for most species. Replication of comprehensive studies is needed for multiple species across a range of areas, Information deficiencies are even greater during the wintering season, when birds require sites that provide security and food resources needed for survival and developing nutrient reserves for spring migration and, possibly, reproduction. Research is needed on many species simply to identify geographic distributions, wintering sites, habitat use, and basic ecology. Studies are complicated, however, by the mobility of birds and by sexual segregation during winter. Stable-isotope methodology has offered an opportunity to identify linkages between breeding and wintering sites, which facilitates understanding the complete annual cycle of birds. The twice-annual migrations are the poorest-understood events in a birds life. Migration has always been a risky undertaking, with such anthropogenic features as tall buildings, towers, and wind generators adding to the risk. Species such as woodland specialists migrating through eastern North America have numerous options for pausing during migration to replenish nutrients, but some species depend on limited stopover locations. Research needs for migration include identifying pathways and timetables of migration, quality and distribution of habitats, threats posed by towers and other tall structures, and any bottlenecks for migration. Issues such as human population growth, acid deposition, climate change, and exotic diseases are global concerns with uncertain consequences to migratory birds and even less-certain remedies. Despite enormous gaps in our understanding of these birds, research, much of it occurring in the past 30 years, has provided sufficient information to make intelligent conservation efforts but needs to expand to handle future challenges.

MODELING THE ECOLOGICAL TRAP HYPOTHESIS: A HABITAT AND DEMOGRAPHIC ANALYSIS FOR MIGRANT SONGBIRDS

Most species occupy both high- and low-quality habitats throughout their ranges. As habitats become modified through anthropogenic change, low-quality habitat may become a more dominant component of the landscape for some species. To conserve species, information on how to assess habitat quality and guidelines for maintaining or eliminating low-quality habitats are needed. We developed a source-sink population model that depicted the annual cycle of a generalized migratory songbird to address these questions. We determined how demographic factors, landscape composition (the percentage of highand low-quality habitat), and habitat selection interacted to promote population persistence or extirpation. Demographic parameters, including adult and juvenile survival, nesting success (probability of a nest successfully fledging one or more young), number of nesting attempts, and number of young fledged per nest, interacted to affect population growth. In general, population growth was more sensitive to adult and juvenile survival than to fecundity. Nevertheless, within typically observed survival values, nest success was important in determining whether the population increased, decreased, or was stable. Moreover, the number of nest attempts by females and the number of young fledged per nesting attempt influenced population stability. This highlights the need to obtain more complete demographic data on species than simple nest success to assess habitat quality. When individuals selected high- and low-quality habitats in proportion to habitat availability, populations persisted as long as low-quality habitat did not make up >40% of the landscapes. However, when individuals preferred low-quality habitats over high-quality habitats, populations were extirpated in landscapes with >30% low-quality habitat because low-quality habitat functioned as an ecological trap, displacing individuals from high-quality to low-quality habitat. For long-term conservation, we emphasize the need for basic information on habitat selection and life-history characteristics of species throughout their range.

Predation of Songbird Nests Differs By Predator and Between Field and Forest Habitats

Our understanding of factors affecting nest predation and ability to mitigate high nest predation rates is hampered by a lack of information on the importance of various nest predator species in different habitats and landscapes. We identified predators of songbird nests in old-field and forest habitats in central Missouri, USA, with miniature video cameras. We used an information-theoretic approach to evaluate support for hypotheses that the importance of predator species varied among habitats and nest stage. We monitored 165 nests with cameras and 272 nests without cameras during 1997-1999, and identified predators at 61 of 74 depredated nests monitored by cameras. Model selection indicated the most support for a model with seperate rates for predation by birds, mammels, and snakes in field and forest habitats. Predation by snakes was greater than predation by mammels and birds in old fields; predation by mammels (mostly rccoons [Procyon lotor]) was greater than by snakes and birds in forest. We found little support for the hypothesis that monitoring nests with cameras effects predation. Nests could not be assigned reliably to a predator group based on condition of the nest. We believe that knowledge of the identity and abundance of dominant predators in a habitat or landscape is neccessary to target conservation efforts to reduce nest predation or to interpret results of research on factors affecting nest success.

Breeding bird populations in Missouri Ozark forests with and without clearcutting

Concern has arisen that forest management practices that create edge (such as clearcutting) are contributing to regional declines in neotropical migrant birds that inhabit forest interiors. Consequently, we studied breeding bird populations in an extensively forested region of southern Missouri to determine if the numbers of breeding birds differed between areas (n = 9) managed by the clearcutting method (CCM), and areas (n = 9) of mature forest with no recent timber harvest or other disturbances (NOHVST). Three forest interior migrants had lower mean densities on CCM sites than NOHVST sites; 3 had greater densities on CCM sites; and densities of 3 others did not differ between treatments. All early successional migrants had greater densities on CCM sites. Numbers of 2 avian nest predators and a brood parasite did not differ on CCM and NOHVST sites. Densities of 9 species differed among regeneration, sapling, and pole-sawtimber habitats on CCM sites.

SONGBIRD NEST PREDATORS IN FOREST–PASTURE EDGE AND FOREST INTERIOR IN A FRAGMENTED LANDSCAPE

Many studies have compared songbird nesting success between forest edge and interior, but few have addressed potential factors underlying variation in nest predation pressure in relation to edge. We examined the relative abundance and species richness of songbird nest predators and the abundance of Brown-headed Cowbirds (Molothrus ater) in forest edge and interior within a fragmented, agricultural landscape in central Missouri, USA. Avian predators and cowbirds were more abundant in forest edges. There were no differences in small- or medium-sized mammalian predator abundance between edge and interior. Almost twice as many snakes were captured in edge as in interior. Predator species richness was significantly higher in forest edge. Forest vegetation structure was very similar between edge and interior, suggesting that differences in predator abundance and species richness were not driven by variation in habitat structure. Nest predator distribution in relation to habitat edge may therefore depend on factors at larger spatial scales, such as landscape context. We suggest that in areas fragmented by agriculture, nest predator assemblages in forest edges may differ from those in forest interior. Edges may attract a greater number of predator species, and some nest predators may be more abundant near the edges of forest patches, although the trend does not apply across all predator taxa. Generalizations about nest predators and edges should thus be made with caution, and conservation plans should consider the composition of local nest predator assemblages in order to predict potential impacts on nesting birds in edge habitat.

Temporal and Spatial patterns of Breeding Brown-Headed Cowbirds in the Midwestern United States

Brown-headed Cowbirds (Molothrus ater) are an obligate brood parasite and a potential threat to some populations of migratory songbirds. I used radio-telemetry to study temporal patterns in behavior, habitat use, and sociality, as well as spatial patterns and movements among breeding, feeding, and roosting areas. I obtained a mean of 42 locations of 84 radio-tagged female cowbirds on three study sites in Illinois and Missouri. Radio-tagged females usually were located in forest and shrub-sapling habitats with a mean of 1.4 males during the morning breeding period. During midmorning to early afternoon, females commuted to short-grass, cropland, and feedlot habitats; they fed in small flocks. At dusk females roosted singly or in small groups near breeding or feeding areas, or commuted to a large communal roost. Behavior and time of day, behavior and habitat use, and habitat use and time of day were highly associated. For approximately 90% of the radio-tagged cowbirds, breeding, feeding, and roosting locations were distributed nonrandomly within home ranges, and came from distinct utilization distributions. Cowbirds moved an average of 3.6 km between roosting and breeding locations, 1.2 km between breeding and feeding locations, and 2.6 km between feeding and roosting locations. Midwestern cowbirds show the same pattern of commuting between disjunct breeding and feeding areas as elsewhere in their range.