Sidney A. Gauthreaux

The Ecological Significance of Behavioral Dominance

In a discussion of the evolution of gene flow, Wilson (1975, p. 103) pointed out that a tendency for different sexes and age groups to migrate differentially can exert a profound influence on social structure. In this paper, I suggest that the reverse is equally true: a basic social structure—namely, the dominance hierarchy—can strongly influence the differential dispersal and migration of different sexes and age groups and thereby serve an important function in population dynamics.

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.

Characteristics of important stopover locations for migrating birds: remote sensing with radar in the Great Lakes basin.

A preliminary stage in developing comprehensive conservation plans involves identifying areas used by the organisms of interest. The areas used by migratory land birds during temporal breaks in migration (stopover periods) have received relatively little research and conservation attention. Methodologies for identifying stopover sites across large geographic areas have been, until recently, unavailable. Advances in weather-radar technology now allow for evaluation of bird migration patterns at large spatial scales. We analyzed radar data (WSR-88D) recorded during spring migration in 2000 and 2001 at 6 sites in the Great Lakes basin (U.S.A.). Our goal was to link areas of high migrant activity with the land-cover types and landscape contexts corresponding to those areas. To characterize the landscapes surrounding stopover locations, we integrated radar and land-cover data within a geographic information system. We compared landscape metrics within 5 km of areas that consistently hosted large numbers of migrants with landscapes surrounding randomly selected areas that were used by relatively few birds during migration. Concentration areas were characterized by 1.2 times more forest cover and 9.3 times more water cover than areas with little migrant activity. We detected a strong negative relationship between activity of migratory birds and agricultural land uses. Examination of individual migration events confirmed the importance of fragments of forested habitat in highly altered landscapes and highlighted large concentrations of birds departing from near-shore terrestrial areas in the Great Lakes basin. We conclude that conservation efforts can be more effectively targeted through intensive analysis of radar imagery.

Priority research needs for the conservation of Neotropical migrant landbirds

Abstract Partners in Flight (PIF) is a consortium of professional and volunteer scientists and educators that promotes the conservation of landbird species. Central to the PIF conservation effort is the development of Bird Conservation Plans specific to each physiographic region of the United States. Without a coordinated prioritization of research needs, land managers, researchers, and funding agencies seeking to conserve landbirds lack direction. To address this issue, we (the Research Working Group of Partners in Flight) identified research priorities that have emerged recently as a result of Bird Conservation Plan development. Research priorities for the coming decade focus on habitat, specifically the identification of high-quality habitats and landscapes for breeding, migration, and wintering. Identification of the scale of breeding and natal dispersal and describing linkages between wintering and breeding populations are also research priorities for the coming decade. A summary of research priorities for each of the PIF regions (Northeast, Midwest, West, and South) is also provided. Specific research needs associated with priority species and habitats in each physiographic area can be accessed in a searchable database: http://www.partnersinflight.org/pifneeds/searchform.cfm.

An Estimate of Avian Mortality at Communication Towers in the United States and Canada

Avian mortality at communication towers in the continental United States and Canada is an issue of pressing conservation concern. Previous estimates of this mortality have been based on limited data and have not included Canada. We compiled a database of communication towers in the continental United States and Canada and estimated avian mortality by tower with a regression relating avian mortality to tower height. This equation was derived from 38 tower studies for which mortality data were available and corrected for sampling effort, search efficiency, and scavenging where appropriate. Although most studies document mortality at guyed towers with steady-burning lights, we accounted for lower mortality at towers without guy wires or steady-burning lights by adjusting estimates based on published studies. The resulting estimate of mortality at towers is 6.8 million birds per year in the United States and Canada. Bootstrapped subsampling indicated that the regression was robust to the choice of studies included and a comparison of multiple regression models showed that incorporating sampling, scavenging, and search efficiency adjustments improved model fit. Estimating total avian mortality is only a first step in developing an assessment of the biological significance of mortality at communication towers for individual species or groups of species. Nevertheless, our estimate can be used to evaluate this source of mortality, develop subsequent per-species mortality estimates, and motivate policy action.

Using a Network of WSR-88D Weather Surveillance Radars to Define Patterns of Bird Migration at Large Spatial Scales

Only one study has examined nocturnal bird migration at a continent-wide scale in North America, and it was limited to four nights in October (Lowery and Newman 1966). Most radar studies of bird migration have been restricted to the surveillance areas of single radars. Few studies have examined simultaneously bird migration at multiple radar sites (e.g., Richardson 1972 gathered data simultaneously from three surveillance radars), and no studies have used a national network of surveillance radars to simultaneously detect, quantify, and monitor migration nightly during migration seasons. The following chapter details a methodology developed in the year 2000 for using the network of 140 Doppler weather surveillance radars (WSR-88D) in the United States (Fig. 1) to study the night-to-night patterns of bird migration in spring and fall at regional and national scales.

Detection and discrimination of fauna in the aerosphere using Doppler weather surveillance radar

Organisms in the aerosphere have been detected by radar since its development in the 1940s. The national network of Doppler weather radars (WSR-88D) in the United States can readily detect birds, bats, and insects aloft. Level-II data from the radar contain information on the reflectivity and radial velocity of targets and on width of the spectrum (SD of radial velocities in a radar pulse volume). Information on reflectivity can be used to quantify density of organisms aloft and radial velocity can be used to discriminate different types of targets based on their air speeds. Spectral width can also provide some useful information when organisms with very different air speeds are aloft. Recent work with dual-polarization radar suggests that it may be useful for discriminating birds from insects in the aerosphere, but more development and biological validation are required.

Importance of the Daytime Flights of Nocturnal Migrants: Redetermined Migration Following Displacement

The daytime flights of nocturnal migrants are examined in relation to the principal axes of migration (P.A.M.) based on calm nights during spring and fall in northwest South Carolina. When nocturnal flights were to the east or west of the calm night directions (30° spring, 232° fall), flights occurred the next morning basically perpendicular to these directions. Because most migrants were displaced east of their P.A.M. in spring and fall, most daytime flights were directed toward the NW, but when nocturnal flights were west of the P.A.M., flights the next morning were to the SE. The daytime redetermined migrations permit the displaced migrants to regain their migratory route by flying the shortest distance.

Correlates of dominance in intraspecific and interspecific interactions of song sparrows and white-throated sparrows

Abstract Behavioural dominance interactions were observed in captive, wintering song sparrows, Melospiza melodia and white-throated sparrows, Zonotrichia albicollis , to determine the correlates of dominance status in interactions within and between these two species. In intraspecific interactions males were dominant to females in both species. Adults were dominant to immatures among white-throated sparrows but not among song sparrows. Interspecific trials showed that song sparrows were generally dominant to larger white-throated sparrows and sex was an important correlate of dominance in interactions between individuals of these two species. Dominance status was negatively correlated with weight loss in both the intraspecific and interspecific trials. These results support the view that behavioural dominance may effectively mediate competition within and between species.

Sun-Compass Orientation in Juvenile Largemouth Bass, Micropterus salmoides

Abstract Juvenile largemouth bass were tested for manifestations of sun-compass orientation. Fish captured from opposite sides of a pond were tested in a circular pool on clear days and on overcast days. When released from the center of the pool on clear days, the fish swam to the wall of the pool in the compass direction that would have taken them to deep water in the pond from which they had been captured the morning of the test. On overcast days the behavior of the fish from one side of the pond was not significantly different from those from the opposite side of the pond.