A. Lawrence Bryan

DEVELOPMENT OF EXPECTATIONS OF LARVAL AMPHIBIAN ASSEMBLAGE STRUCTURE IN SOUTHEASTERN DEPRESSION WETLANDS

We surveyed larval amphibians and fish in 25 relatively pristine depression wetlands on the upper Atlantic coastal plain of South Carolina to examine relationships among hydroperiod length, fish presence/absence and larval amphibian assemblage structure. Our goals were to test the application of general models of lentic community structure to Southeastern depression wetlands and to develop expectations of larval amphibian assemblage structure at reference sites. Amphibian species richness showed a unimodal pattern along a hydroperiod gradient, with wetlands that contained water for 8–10 mo/yr having the highest species richness. Wetlands that contained water for longer periods (i.e., dried only during severe drought) often contained fish and had relatively low amphibian species richness. Most species occurred along a restricted portion of the hydroperiod gradient, and some species were found almost exclusively in wetlands with fish. Associations among the occurrence of species led to relatively discrete breaks in assemblage structure along the hydroperiod gradient. Canonical correspondence analysis of catch-per-unit-effort data identified four groups of wetlands with similar assemblage structure: (1) short (drying in spring), (2) medium (drying in summer), and (3) long (drying in fall or semi-annually) hydroperiod wetlands without fish; and (4) long hydroperiod wetlands with fish. Our results suggest that general models of community structure in lentic systems are applicable to southeastern isolated wetlands and should form the basis for developing expectations of larval amphibian assemblage structure in these systems.

The Effects of Drought on Foraging Habitat Selection of Breeding Wood Storks in Coastal Georgia

Little is known about the feeding ecology and breeding success of the Lesser Flamingo (Phoeniconaias minor) and Greater Flamingo (Phoenicopterus ruber roseus) on the ephemeral salt lake of the Makgadikgadi, Botswana. Some observations of large numbers of both species have been recorded breeding on the Makgadikgadi salt pans, and it is believed that this site is among the most important breeding sites for both species of flamingo in Africa. This paper addresses the importance of the Makgadikgadi salt pans by revising some of the observations made in the past and also introduces a long-term research project that is currently underway to determine more about the ecology of the pans and the flamingo breeding success at this important site.

Low levels of genetic variability in north American populations of the Wood Stork (Mycteria americana)

The breeding population of Wood Storks (Mycteria americana) in the southeastern United States has declined since the 1930s, resulting in the listing of all United States populations of the species as endangered in 1984. We assessed genetic structure within and among nine colonies of Wood Storks from Georgia and Florida. Levels of band sharing based on multilocus oligonucleotide DNA fingerprinting of individuals from seven colonies ranged from 58% among nests within the same tree to approximately 55% within the same colony. Levels of band sharing were similar to those reported for other populations of birds that have experienced drastic reductions in population size. A more thorough analysis of four polymorphic microsatellite loci for 136 individuals from nine colonies indicated low levels of allelic diversity and low genetic divergence among colonies. Genetic differentiation (F ST = 0.015) was similar to levels detected from allozymes for 15 colonies of Wood Storks in Florida (F ST = 0.019). These data, together with demographic studies of these populations, indicated high levels of gene flow among colonies (N m = 16.4). In agreement with previous studies, we recommend that all colonies of Wood Storks in the southeastern United States be managed on a regional basis as a single interbreeding population. Similar genetic surveys of the disjunct breeding populations of Wood Storks in South America and Central America would be beneficial in understanding the total genetic differentiation in the species.

MERCURY IN BALD EAGLE NESTLINGS FROM SOUTH CAROLINA, USA

Bald eagles (Haliaeetus leucocephalus) may be at risk from contaminants in their diet and young birds may be particularly sensitive to contaminant exposure. To evaluate potential risks from dietary mercury exposure to eagle nestlings in South Carolina (USA), we surveyed mercury concentrations in 34 nestlings over two breeding seasons (1998 and 1999). Samples were also obtained from several post-fledging eagles in the region. Nestling feather mercury ranged from 0.61–6.67 μg Hg/g dry weight, nestling down mercury from 0.50–5.05 μg Hg/g dry weight, and nestling blood mercury from 0.02–0.25 μg Hg/g wet weight. We did not detect significant differences in tissue mercury between nestlings from coastal and inland regions in contrast to some other studies of piscivorous birds. Mercury concentrations were much higher in the post fledging birds we sampled. Our data show that nestling eagles in South Carolina are accumulating mercury, and that concentrations in older birds may exceed regulatory guidelines.

Mercury Concentrations in Nestling Wading Birds Relative to Diet in the Southeastern United States: A Stable Isotope Analysis

Mercury (Hg) is a ubiquitous environmental contaminant that is transferred trophically through aquatic and terrestrial food webs. To better understand the routes of Hg uptake in organisms that rely on both aquatic and terrestrial food resources, we analyzed feather and down samples from nestling wading birds of varying trophic positions in both inland and coastal colonies. We used stable nitrogen and carbon isotope analyses to evaluate trophic positions of individual species (δ15N) and differences in foraging habitat use (δ13C). Inland, aquatic species had higher trophic status than the single terrestrial species examined, and the expected positive relationship between δ15N and Hg content of feathers was observed. However, the same was not true for all species from coastal colonies. Feathers from species that primarily consumed saltwater prey were relatively high in δ15N value and low in Hg content, which is opposite of the trend expected due to Hg biomagnification in food chains. In contrast, coastal species foraging in freshwater or a combination of freshwater and saltwater habitats displayed greater Hg contents in feathers. The apparent differential use of the two aquatic systems (freshwater and saltwater) in coastal environments by wading bird species results in variations in δ15N values and Hg contents in nestling feathers not found in species associated with only freshwater systems.

Satellite Tracking Large-scale Movements of Wood Storks Captured in the Gulf Coast Region

Abstract Wood Storks (Mycteria americana) breeding in the southeastern United States exhibit lengthy inter- and intra-regional movements in response to resource availability. One type of movement, post-breeding dispersal, has resulted in storks from this population temporarily moving into the Gulf Coast states of Alabama and eastern Mississippi. Concurrently, other Wood Storks, presumably of Mexican/Central American origin, are frequently observed in large numbers in the Mississippi River Valley and nearby western states during the late-summer months and the proximity of dispersing storks from the two regions might result in population mixing. In a preliminary examination of the origins of Wood Storks observed in Gulf Coast states and the likelihood of population mixing, we deployed ten satellite transmitters on storks in those areas in June-July of 2003 and monitored their movements. All storks captured in eastern Mississippi moved into southern Florida. Storks captured in western Mississippi went to eastern Mexico or western Guatemala. One stork from Louisiana went to Mexico and the other went to southern Florida, suggesting that population mixing may be occurring on their non-breeding season habitats.

A Preliminary Model of Wood Stork Population Dynamics in the Southeastern United States

Abstract We modeled population dynamics and extinction probabilities for the endangered Wood Stork (Mycteria americana) using count data from synoptic aerial surveys, annual measures of productivity from throughout the southeastern U.S., and survival data from satellite-tagged juveniles. Using a simple, count-based diffusion approximation approach we were able to quantify an increasing population trend since 1976. High inter-year variability resulted in wide confidence intervals and we could not eliminate the possibility of long-term population decline in spite of recently measured population increases. We also used a stage-based population matrix model to incorporate observed differences in survival rates among age classes. Fledging success, and survival of fledglings, one, and two-year-old birds were estimated using data from the satellite telemetry study. Because the survival rates of three-year-olds and adults are presently unknown, we analyzed population dynamics over a range of these values. Long-term population growth was most sensitive to changes in adult survivorship. This deterministic matrix model indicated that adult survival rates >0.94 were necessary to maintain a growing population, an estimate considerably higher than that observed in the European White Stork (Ciconia ciconia). This study underscores the need for reliable estimates of juvenile and adult survival in Wood Storks, and for a conservation focus on the factors that affect adult survival. It also provides a tool for understanding and projecting potential trajectories of the Wood Stork population in the Southeastern United States.

Breeding Success of Wood Storks Nesting in Georgia and South Carolina

Abstract Determination of breeding success rates of endangered species such as the Wood Stork (Mycteria americana) and reasons for their variation are vital information needed for monitoring recovery efforts. To provide information in the northern portion of their breeding range, breeding success rates were monitored for nine stork colonies in Georgia and South Carolina in 2004 and 2005. Overall success rates were very high in 2004 (N = 421, x̄ = 2.3 fledged young per nesting attempt), with slightly greater success in inland colonies as compared to coastal colonies. Overall success rates declined in 2005 (N = 359, x̄ = 1.6 fledged young per nesting attempt), with slightly greater success in coastal colonies as compared to inland colonies. Reduced success in 2005 may be due to elevated mid-breeding season rainfall and its negative effects on prey availability. Examination of longer-term breeding success at multiple Georgia stork colonies relative to annual rainfall showed no consistent trends between success and mid-season rainfall. A moderate positive association was found between pre-breeding season rainfall and success for coastal, but not inland, colonies.

Parental Activities of Nesting Wood Storks Relative to Time of Day, Tide Level and Breeding Stage

Abstract In 1995, parental activities of Wood Storks (Mycteria americana) were monitored in three coastal colonies during a series of 24-h long observation periods to document attendance, foraging, and other activities in relation to time of day, tide level, and breeding stage. During 5,400 nest-hours of observations, nest attendance declined and feeding rates increased with nestling developmental stage. Although some feeding arrivals occurred during darkness, the great majority of arrivals (including feeding) occurred during daylight periods. Mean times of return from feeding trips varied significantly among colonies and nestling developmental stages. Feeding arrivals were linked to tides, suggesting that most foraging occurred during the preceding low tide period. Inter-colony variation in foraging arrival times and interactions with tides were likely associated with differences in proximity to foraging sites and availability of both tidal and non-tidal (freshwater) foraging habitats.

Fine-scale assessment of home ranges and activity patterns for resident black vultures ( Coragyps atratus ) and turkey vultures ( Cathartes aura )

Knowledge of black vulture (Coragyps atratus) and turkey vulture (Cathartes aura) spatial ecology is surprisingly limited despite their vital ecological roles. Fine-scale assessments of space use patterns and resource selection are particularly lacking, although development of tracking technologies has allowed data collection at finer temporal and spatial resolution. Objectives of this study were to conduct the first assessment of monthly home range and core area sizes of resident black and turkey vultures with consideration to sex, as well as elucidate differences in monthly, seasonal, and annual activity patterns based on fine-scale movement data analyses. We collected 2.8-million locations for 9 black and 9 turkey vultures from June 2013 –August 2015 using solar-powered GSM/GPS transmitters. We quantified home ranges and core areas using the dynamic Brownian bridge movement model and evaluated differences as a function of species, sex, and month. Mean monthly home ranges for turkey vultures were ~50% larger than those of black vultures, although mean core area sizes did not differ between species. Turkey vulture home ranges varied little across months, with exception to a notable reduction in space-use in May, which corresponds with timing of chick-rearing activities. Black vulture home ranges and core areas as well as turkey vulture core areas were larger in breeding season months (January–April). Comparison of space use between male and female vultures was only possible for black vultures, and space use was only slightly larger for females during breeding months (February–May). Analysis of activity patterns revealed turkey vultures spend more time in flight and switch motion states (between flight and stationary) more frequently than black vultures across temporal scales. This study reveals substantive variability in space use and activity rates between sympatric black and turkey vultures, providing insights into potential behavioral mechanisms contributing to niche differentiation between these species.