Leonard R. Reitsma

Moisture as a determinant of habitat quality for a nonbreeding Neotropical migratory songbird

Identifying the determinants of habitat quality for a species is essential for understanding how populations are limited and regulated. Spatiotemporal variation in moisture and its influence on food availability may drive patterns of habitat occupancy and demographic outcomes. Nonbreeding migratory birds in the neotropics occupy a range of habitat types that vary with respect to moisture. Using carbon isotopes and a satellite-derived measure of habitat moisture, we identified a moisture gradient across home ranges of radio-tracked Northern Waterthrush (Seiurus noveboracensis). We used this gradient to classify habitat types and to examine whether habitat moisture correlates with overwinter mass change and spring departure schedules of Northern Waterthrush over the late-winter dry season in the tropics. The two independent indicators of moisture revealed similar gradients that were directly proportional to body mass change as the dry season progressed. Birds occupying drier habitats declined in body mass over the study period, while those occupying wetter habitats increased in body mass. Regardless of habitat, birds lost an average of 7.6% of their mass at night, and mass recovery during the day trended lower in dry compared with wet habitats. This suggests that daily incremental shortfalls in mass recovery can lead to considerable season-long declines in body mass. These patterns resulted in consequences for the premigratory period, with birds occupying drier habitats having a delayed rate of fat deposition compared with those in wet habitats. Taken together with the finding that males, which are significantly larger than females, are also in better condition than females regardless of habitat suggests that high-quality habitats may be limited and that there may be competition for them. The habitat-linked variation in performance we observed suggests that habitat limitation could impact individual and population-level processes both during and in subsequent periods of the annual cycle. The linkage between moisture and habitat quality for a migratory bird indicates that the availability of high-quality habitats is dynamic due to variation in precipitation among seasons and years. Understanding this link is critical for ascertaining the impact of future climate change, particularly in the Caribbean basin, where a much drier future is predicted.

White Phosphorus Poisoning of Waterfowl in an Alaskan Salt Marsh

The cause of the yearly death of an estimated 1,000 to 2,000 migrating dabbling ducks (Anas spp.) and 10 to 50 swans (Cygnus buccinator and C. columbianus) has remained a mystery for the last ten years in Eagle River Flats (ERF), a 1,000 ha estuarine salt marsh near Anchorage, Alaska, used for artillery training by the U.S. Army. We have gathered evidence that the cause of this mortality is the highly toxic, incendiary munition white phosphorus (P4). The symptoms of poisoning we observed in wild ducks included lethargy, repeated drinking, and head shaking and rolling. Death was preceded by convulsions. Farm-reared mallards dosed with white phosphorus showed nearly identical behavioral symptoms to those of wild ducks that became sick in ERF. White phosphorus does not occur in nature but was found in both the sediments where dabbling ducks and swans feed and in the gizzards of all carcasses collected in ERF. We hypothesize that feeding waterfowl are ingesting small particles of the highly toxic, incendiary munition P4 stored in the bottom anoxic sediments of shallow salt marsh ponds.

Habitat Selection and Site Fidelity of Canada Warblers (Wilsonia Canadensis) in Central New Hampshire

Abstract Habitat selection by migratory bird species affects their fitness. Studies of populations with marked individuals of known reproductive performance provide the greatest insight on the relationship between a species and the range of habitats it occupies. Canada Warblers (Wilsonia canadensis) have not been intensively investigated at the population level, despite significant regional declines in their numbers over the past 40 years (e.g., 4.6% year−1 in New Hampshire). We mapped 92 male territories over four years and quantified habitat structure and habitat composition for territories and nonterritory areas. Analyses revealed more shrubs (stems and foliage), more perch trees, and lower canopy height on territories. Birds returned at an average rate of 52.0 ± 2.96% (SE) and exhibited average between-year shifts of 32 m in territory locations. Over the four years, males had high pairing success (91.0 ± 5.61%). Three-quarters of paired males fledged at least one young. Pairing and fledging success did not influence site fidelity. Paired males had more shrub stems and song-perch trees. Territories of earlier-arriving males had more shrub stems. The high proportion of males pairing and successfully fledging young, together with the high average return rates, indicate that areas with dense subcanopy vegetation constitute prime Canada Warbler breeding habitat in New Hampshire. Timber harvest practices that result in high shrub density and residual standing trees, such as deferment or two-age harvest, have the potential to slow Canada Warbler population declines, but only if they are widely applied in forest management.

SITE FIDELITY AND EPHEMERAL HABITAT OCCUPANCY: NORTHERN WATERTHRUSH USE OF PUERTO RICAN BLACK MANGROVES DURING THE NONBREEDING SEASON

Abstract We studied the dispersion of Northern Waterthrushes (Seiurus novaboracensis) in southwestern Puerto Rico during four nonbreeding seasons, 1996–1999. Densities were high (up to 13 birds/ha) on a 3-ha mature black mangrove (Avicennia germinans) study plot, but were significantly lower during periods of high water levels. Individuals exhibited site fidelity within and between seasons. Feeding areas were small (mean = 0.074 ha ± 0.041 SD) and there was considerable overlap tolerated among conspecifics. Waterthrush density decreased when water submerged their primary foraging substrate: woody debris and pneumatophores. Interannual returns were similar to other Neotropical migrants (mean = 50%) but site persistence was low due to periodic flooding. In September 1998, hurricane Georges flooded the plot and blew down >90% of the black mangrove trees. This drastic habitat alteration was followed by a drastic decline in waterthrushes using the study area. Individuals left feeding areas for overnight roost sites in red mangroves (Rhizophora mangle). This latter finding, coupled with site fidelity and high return rates concurrent with low site persistence, suggests that waterthrushes exhibit high plasticity in their use of habitat during the nonbreeding season, but may rely upon mangroves for overwinter survival.

Influence of Moisture and Food Supply on the Movement Dynamics of a Nonbreeding Migratory Bird (Parkesia Noveboracensis) in a Seasonal Landscape

ABSTRACT. We radiotracked Northern Waterthrushes (Parkesia noveboracensis) in four habitats in Puerto Rico during two winters (i.e., January–April) in 2003 and 2004 to determine the ecological determinants of diurnal space use and overwinter sitepersistence in this species. The majority of birds (69%) were sedentary and used a contiguous area within a single habitat over the winter period. A smaller percentage (31%) initially used a contiguous area within a single habitat but then permanently moved from that area to another disjunct location (mean = 418 m). Most of these movements were out of the two habitats (dry forest and Black Mangrove) that became the driest from January to mid-March and into wetter mangrove areas. The primary determinants of movement probability were moisture and food availability on each birds home range. Foraging areas of birds that eventually moved were drier and had lower food availability than areas used by site-persistent individuals. The sites that these itinerant birds moved to were wetter and had higher food availability, which suggests that individuals moved in response to changing resources. Our results (1) indicate that habitats used by this species differ in suitability and (2) support previous findings that turnover rates within a habitat could serve as an indicator of habitat quality. The ability to predict behavioral responses of individuals to habitat conditions that vary across space and time is essential for understanding individual and population responses to habitat loss and the effects of a changing climate in the New World tropics.

Multiple Space-Use Strategies and Their Divergent Consequences in a Nonbreeding Migratory Bird (Parkesia noveboracensis)

ABSTRACT. We investigated the relationships among space-use patterns, home-range attributes, and individual characteristics to determine the consequences of different space-use strategies for the overwinter physical condition of Northern Waterthrushes (Parkesia noveboracensis). We have elsewhere demonstrated that heterogeneity in food availability drives the movement decisions of site-persistent and itinerant individuals during the nonbreeding period. Here, we show that intraspecific competition played an important role in determining where individuals initially and eventually settled. Territoriality, characterized by aggression, site-persistence, and exclusive home ranges, was more often found in males. Territorial birds gained mass over the winter, whereas birds that made midseason home-range shifts or that had home ranges with high intraspecific overlap tended to lose mass over the winter. The benefits associated with territoriality may be the result of maintaining higher-quality territories that were both wetter and had higher food availability than less exclusive home ranges. Our results suggest that despotism in the form of territoriality drives patterns of habitat occupancy, and in this system, high-quality habitat appears to be limiting for the Northern Waterthrush. This may have long-term consequences for the success of individual birds, because continued destruction of naturally limited habitats such as coastal mangroves, and predictions of a drying climate on wintering areas, have the potential to severely affect populations.

Does age influence territory size, habitat selection, and reproductive success of male Canada Warblers in central New Hampshire?

Abstract The Canada Warbler (Wilsonia canadensis) is currently in decline in the northeastern United States and basic demographic parameters remain to be described. We studied marked populations (76 ASYs, 14 SYs, and 2 of unknown age) of Canada Warblers on two study sites from 2003 to 2006. We mapped 92 territories (including males returning in multiple years) of 71 males using handheld GPS and ArcMap. We compared the pairing and fledging success of older and younger males on both sites, a red maple (Acer rubrum) swamp and a young forest intensively harvested in 1985 with ∼10% residual standing trees used by males as song perch trees. Both sites had a high proportion of ASYs (84% ASY for all territorial males, 77.5% of all males including non-territorial individuals). Both pairing (91%) and fledging (78%) success was comparatively high suggesting these two sites were of high value to this species. A higher proportion of SYs were transients. Pairing success was lower for younger males which established territories, but paired SYs fledged at least one young at a rate comparable to older males. This study corroborates the benefits of age and experience to reproductive performance. The results suggest that both red maple swamps and post-harvest forests with thick subcanopy vegetation and emergent trees provide high quality habitat for breeding Canada Warblers.

Habitat Use of the Louisiana Waterthrush During the Non-Breeding Season in Puerto Rico

Abstract We used radiotelemetry to quantify habitat and spatial use patterns of neighboring Louisiana Waterthrush (Parkesia motacilla) along two streams in the Caribbean National Forest in Puerto Rico during 2005–2007. Home range sizes varied with younger birds having larger home ranges and core areas than older birds. All birds occupied some length of stream but a wide range of off-stream habitats were also used. Off-stream habitats included a range of disturbance from residential areas to small saturated pastures. Neighbors exhibited a wide range of overlap in home ranges (x¯  =  20%) and older birds had more overlap than younger birds. The greatest percent of foraging time was along streams (64.4%) followed by muddy substrate (26.5%), housing developments (7.4%), and roads (1.7%). The greater proportion of time foraging along streams indicates this is the preferred habitat for this species. Use of off-stream habitat indicates a strategy of exploiting food-rich ground substrates, and in particular those with high moisture.

Community–based conservation in East Africa: a case study of Western Usambara Mountains, Tanzania

Multiple regions in East Africa face challenges due to increased rates of resource consumption and species extinction. We examined how well community–based conservation minimizes habitat loss for wildlife and marginalization of under–represented people. Using ecological field work and ethnographic techniques, we focused on how current land use in the Usambara Mountains, Tanzania, affects the ecology and social fabric of the area. We found low recruitment potential of non–native agricultural crops into adjacent forest reserves. We also found that certain agricultural practices that increase sustainability are slowly being integrated while others are still met with resistance. Communication between stakeholders has begun; however, without cooperation amongst key players the long–term future for wildlife and local people will be increasingly threatened as resource pressure intensifies.