David N. Ewert

Impact of Hurricane Hugo on bird populations on St. John, U.S. Virgin Islands

Bird populations were surveyed in Virgin Islands National Park, St. John, U.S. Virgin Islands in 1987 (two years before Hurricane Hugo hit the Virgin Islands) and in 1990 (four months after the hurricane). Abundance was estimated using the fixed-radius point count method. The average number of individual permanent residents per survey point was significantly lower after the hurricane in both moist forest and dry evergreen woodland. Most of the resident species that showed substantial population declines feed primarily on fruit or nectar, a pattern which is consistent with the results of several other recent studies of the effect of hurricanes on forest bird communities. Also, an insectivorous winter resident (Parula americana) had significantly lower densities after the hurricane. Although many areas within the park were defoliated after the hurricane, most trees remained standing and they began to produce new leaves within a few weeks. Our results suggest that even relatively mild storm damage can result in a marked reduction in the numbers of some species of birds due either to mortality or dispersal from the affected area.

Positive Relationships Between Association Strength and Phenotypic Similarity Characterize the Assembly of Mixed-Species Bird Flocks Worldwide

Competition theory predicts that local communities should consist of species that are more dissimilar than expected by chance. We find a strikingly different pattern in a multicontinent data set (55 presence-absence matrices from 24 locations) on the composition of mixed-species bird flocks, which are important subunits of local bird communities the world over. By using null models and randomization tests followed by meta-analysis, we find the association strengths of species in flocks to be strongly related to similarity in body size and foraging behavior and higher for congeneric compared with noncongeneric species pairs. Given the local spatial scales of our individual analyses, differences in the habitat preferences of species are unlikely to have caused these association patterns; the patterns observed are most likely the outcome of species interactions. Extending group-living and social-information-use theory to a heterospecific context, we discuss potential behavioral mechanisms that lead to positive interactions among similar species in flocks, as well as ways in which competition costs are reduced. Our findings highlight the need to consider positive interactions along with competition when seeking to explain community assembly.

Song sharing and repertoires among migratory and resident rufous-sided towhees

Among oscines, song sharing with neighbors and large song repertoires may be enhanced in resident populations. This idea was explored with the Rufous-sided Towhee (Pipilo erythrophthalmus) by studying singing behavior in a resident Florida and a migratory New York population. Florida males (n = 15) sang an average of eight song types per male, but New York males (n = 15) sang only 3.5. Furthermore, unlike the New York males, the Florida males shared most song types in their larger repertoires with immediate neighbors. These marked differences in sharing and repertoires need further study in the towhees and other species in order to understand more clearly the processes that lead to such population differences.

SPATIAL VARIATION IN FORAGING OF THE BLACK-THROATED GREEN WARBLER ALONG THE SHORELINE OF NORTHERN LAKE HURON'

The Great Lakes strongly influence local climate, vegetation, and animal com- munities, all of which are important to both migrating and breeding birds. This influence can be considerable during springtime in nearshore habitats, as onshore winds depress air temperatures, delaying development of shoreline vegetation relative to inland areas. These developmental differences also may affect abundance, distribution, activity, and growth of insect prey, resulting in spatially-related differences in foraging by birds. Here we test the hypothesis that northern Lake Huron influences the foraging behavior of Black-throated Green Warblers (Dendroica virens) during both migratory periods and the breeding season. We detected spatial variation in a number of variables we used to describe foraging, with most differences occurring during spring migration. We suggest that birds primarily varied foraging in response to spatial differences in prey resulting from microclimatic influences of nearby Lake Huron. We also suggest that emerging aquatic insects in shoreline habitats, primarily midges (Diptera: Chironomidae), are important to birds and propose that this

Flocking behavior of migratory warblers in winter in the virgin Islands

We assessed the flocking behavior of birds on St. John and St. Thomas, U.S. Virgin Islands, with systematic surveys along trails in moist forests. Winter residents (species breeding in North America and that winter in the Virgin Islands), all of which were warblers, comprised 91% of the individuals found in 28 flocks but only 49% of solitary individuals. The average flock size was 4.0 individuals of 3.1 species, and did not differ between St. John and St. Thomas even though the average forest tract on St. John (1,000 ha) was much larger than on St. Thomas (62 ha). Northern Parula (Parula americana) and Black-andwhite Warbler (Mniotilta varia), the most common species in flocks, occurred in 76% and 79% of the flocks, respectively. Northern Parula flocked significantly more frequently on St. Thomas than on St. John, but no other species showed a difference in flocking behavior between the two islands. Each flock typically included one individual of each species.

KIRTLAND'S WARBLERS IN ANTHROPOGENICALLY DISTURBED EARLY-SUCCESSIONAL HABITATS ON ELEUTHERA, THE BAHAMAS

Abstract. To characterize the nonbreeding habitat of Kirtlands Warbler (Dendroica kirtlandii) on Eleuthera, The Bahamas, we quantified the habitat at sites where we captured the warblers and compared these traits with those of random sites and sites of tall coppice. On the basis of a chronosequence of satellite imagery, 153 capture sites ranged in age from 3 to 28 years after human disturbance, mean 14.6 years ± 6.3 (SD). Capture sites had been abandoned after clearing (65%), converted to goat pasture (26%), burned (2%), or were young second growth following unknown disturbance (7%). Canopies in 104 capture plots were lower (mean 1.8 m) than canopies in random plots (mean 2.7 m) and plots of late-successional tall coppice (mean 6.3 m). At seven sites mean foliage density in capture plots was consistently greatest at 0.5 to 1.0 m height, but the sites were heterogeneous for other foliage-height classes <3 m and for time since disturbance, canopy height, stem density, and five ground-cover traits. Plots did not differ by the sex of the captured bird except for a difference (P = 0.05) in foliage density at heights <3 m. Kirtlands Warblers frequently consumed fruit (69% of 499 observations), especially from Lantana involucrata, Erithalis fruticosa, and Chiococca alba. Foliage of these plants was more abundant in capture plots than random plots. Because the warblers consume fruit extensively and fruit is more abundant in early successional habitat, this species, like other nearctic—neotropical migrants that breed in early successional habitats, is absent from mature forests on the wintering grounds.

SPATIAL FORAGING DIFFERENCES IN AMERICAN REDSTARTS ALONG THE SHORELINE OF NORTHERN LAKE HURON DURING SPRING MIGRATION

Abstract Lowland coniferous forests adjacent to northern Lake Huron provide important stopover habitat for landbirds during spring migration. Large numbers of aquatic insects emerging from nearshore waters of northern Lake Huron appear to be an important food source. In this study we compared the foraging behavior of a long-distance landbird migrant, the American Redstart (Setophaga ruticilla), in areas with high densities of emergent aquatic insects to areas with few or no emergent aquatic insects to assess the significance of these arthropods as an early spring food source. Redstarts foraged differently in shoreline habitats relative to inland habitats of similar vegetation composition. Both males and females gleaned significantly more in shoreline habitats as compared to inland areas of similar vegetation composition, and inland birds performed more sally strikes than birds at the shoreline. Both sexes also varied the use of tree species in which they foraged. Redstarts used northern white cedar (Thuja occidentalis) more at shoreline than inland, while inland redstarts foraged in deciduous trees more than at the shoreline. We suggest that differences in foraging between shoreline and inland locations were responses to differences in prey types and abundance, most notably the presence of emergent aquatic insects (Diptera: Chironomidae) in shoreline habitat. Our results complement those of previous work, suggesting that midges provide a critical early season resource for landbirds migrating through Michigans eastern Upper Peninsula during spring.

Distribution of Migratory Landbirds Along the Northern Lake Huron Shoreline

Abstract The distribution of landbirds during migration in forested landscapes of eastern North America is poorly known. We describe (1) the distribution of landbirds in northern white cedar (Thuja occidentalis) dominated forests as a function of distance from northern Lake Huron in Michigan during spring and autumn migration, and (2) discuss factors that may affect the distribution of these migrants. Both long- and short-distance migrants in spring and fall were concentrated within 0.4 km of the Lake Huron shoreline. This pattern was particularly pronounced during spring when aquatic-hatched insects such as midges and their predators (e.g., spiders) are most common and occur in largest numbers near the shoreline. Both long- and short-distance migrant abundance was associated with midge abundance, after controlling for date, during spring migration but not during fall migration. Migrants may concentrate near the shoreline because of the barrier effect of Lake Huron and relatively abundant food resources, especially during spring migration. Terrestrial habitats adjacent to bodies of water, where aquatic-dependent invertebrates are relatively abundant may provide important stopover sites for landbird migrants. Our results suggest coastal areas within the Great Lakes region provide critical stopover habitat for landbird migrants and should be a focus of conservation efforts, especially given the increasing development pressure that threatens these areas.

Duration and Rate of Spring Migration of Kirtland's Warblers

Abstract The duration of migration of the endangered Kirtlands Warbler (Setophaga kirtlandii) has not been previously documented. We estimated the average duration of spring migration for five male Kirtlands Warblers by observing uniquely color-banded individuals at or near both the beginning and end of spring migration in Eleuthera, The Bahamas, and Michigan, respectively. We estimated the average duration of spring migration for these five individuals to have been no more than 15.8 days (range 13–23 days) and the average distance traveled to have been 144.5 km/day (96.1–169.1 km/day).

Ecosystem management in the eastern Upper Peninsula of Michigan: A case history

Abstract In 1992, a group composed of state and federal government agencies, a non-government organization, and industrial land holders formed to coordinate management efforts in the eastern Upper Peninsula of Michigan (EUP). The EUP landscape, characterized by a variety of glacial landforms, encompasses 1.6 million ha. Members of the group represent organizations that manage two-thirds of the land in the EUP. The groups mission is to facilitate complementary management of public and private lands for all appropriate uses, using an ecological approach to sustain and enhance representative ecosystems, globally significant communities and landscapes, and threatened and endangered species. Several factors make this a challenging mission. First, the EUP contains a wide variety of ecological units, each with a unique suite of species and management considerations. Second, the management goals of the stakeholders are diverse, ranging from preservation of natural and cultural resources to economically profitable timber production. Finally, the group has to deal with many of the issues that have recently received national attention: threatened and endangered species management, forest fragmentation, old growth, deer browsing, fire management, forest conversion, effects of management decisions on local and regional economies, and maintenance of ecosystem function. This paper chronicles the efforts and group dynamics of the eastern Upper Peninsula Ecosystem Management Group. The complexity of managing a large and diverse area is illustrated by describing the areas ecology and biological significance, ownership patterns, and management goals of stakeholders. Partners work together informally, making decisions by consensus, stressing communication, understanding, and cooperation, rather than formal procedures and protocols. Working this way, the group communicates openly and honestly and has established working relationships built on trust. We also highlight accomplishments to date including the development of an ecological classification system that serves as a foundation for our efforts. We conclude with a discussion of the direction and projected activities of the group and obstacles the group faces.