Jason M. Townsend

Ancient islands and modern invasions: disparate phylogeographic histories among Hispaniola's endemic birds.

With its large size, complex topography and high number of avian endemics, Hispaniola appears to be a likely candidate for the in situ speciation of its avifauna, despite the worldwide rarity of avian speciation within single islands. We used multilocus comparative phylogeography techniques to examine the pattern and history of divergence in 11 endemic birds representing potential within‐island speciation events. Haplotype and allele networks from mitochondrial ND2 and nuclear intron loci reveal a consistent pattern: phylogeographic divergence within or between closely related species is correlated with the likely distribution of ancient sea barriers that once divided Hispaniola into several smaller paleo‐islands. Coalescent and mitochondrial clock dating of divergences indicate species‐specific response to different geological events over the wide span of the island’s history. We found no evidence that ecological or topographical complexity generated diversity, either by creating open niches or by restricting long‐term gene flow. Thus, no true within‐island speciation appears to have occurred among the species sampled on Hispaniola. Divergence events predating the merging of Hispaniola’s paleo‐island blocks cannot be considered in situ divergence, and postmerging divergence in response to episodic island segmentation by marine flooding probably represents in situ vicariance or interarchipelago speciation by dispersal. Our work highlights the necessity of considering island geologic history while investigating the speciation–area relationship in birds and other taxa.

Winter Territoriality and Spatial Behavior of Bicknell's Thrush (Catharus bicknelli) at Two Ecologically Distinct Sites in the Dominican Republic

ABSTRACT. We used radiotelemetry to investigate the spatial behavior of wintering Bicknells Thrushes (Catharus bicknelli) at a mid-elevation rainforest site and a high-elevation cloud-forest site in the Dominican Republic. We also analyzed blood stable carbon isotopes and fecal samples to compare thrush diets at these two floristically and climatically distinct sites. Birds consumed a primarily fruit-based diet at the mid-elevation site and a primarily arthropod-based diet at the high-elevation site. Despite these dietary differences, individuals at both sites defended and maintained exclusive, minimally overlapping core use areas and home ranges. The mean size of both core use areas and home ranges was similar between males and females and between adults and first-winter birds. Presence of nonterritorial or “floater” individuals was low at both sites (2.7% and 5.6%). Birds at the arthropod-dominated site were observed significantly more often on or within 1 m of the ground than birds at the fruit-heavy site, which were more often observed in the mid-canopy structure above 2 m. Birds at both sites displayed agonistic behaviors toward conspecifics and toward playback of conspecific vocalizations. Exclusive territoriality was the predominant winter social system, and we suggest that both arthropods and fruit are defensible resources for wintering Bicknells Thrushes.

Avian, salamander, and forest floor mercury concentrations increase with elevation in a terrestrial ecosystem

High-elevation ecosystems of the northeastern United States are vulnerable to deposition and environmental accumulation of atmospheric pollutants, yet little work has been done to assess mercury (Hg) concentrations in organisms occupying montane ecosystems. The authors present data on Hg concentrations in ground-foraging insectivorous songbirds, a terrestrial salamander, and forest floor horizons sampled along a forested elevational gradient from 185 m to 1273 m in the Catskill Mountains, New York, USA. Mean Hg concentrations in Catharus thrushes and the salamander Plethodon cinereus increased with elevation, as did Hg concentrations in all forest floor horizons. Mean Hg concentrations in organic soils at approximately 1200 m elevation (503.5 ± 17.7 ng/g, dry wt) were 4.4-fold greater than those at approximately 200 m. Montane ecosystems of the northeastern United States, and probably elsewhere, are exposed to higher levels of atmospheric Hg deposition as reflected in accumulation patterns in the forest floor and associated high-elevation fauna. This information can be used to parameterize and test Hg transport and bioaccumulation models of landscape-specific patterns and may serve as a monitoring tool for decision makers considering future controls on Hg emissions. Further investigation is needed into the potential effects of increased Hg concentrations on high-elevation fauna.

Phylogeography and conservation of the endemic Hispaniolan Palm-Tanagers (Aves: Phaenicophilus)

The Gray-crowned Palm-Tanager (Phaenicophilus poliocephalus), sometimes considered conspecific with its more widespread congener P. palmarum, is restricted to Haiti’s Tiburon Peninsula, a biodiversity hotspot threatened by extensive habitat loss. We used a multilocus phylogeographic approach to identify evolutionarily distinct populations of Phaenicophilus. Mitochondrial haplotypes formed two reciprocally monophyletic groups separated by 5% uncorrected divergence. Genealogical patterns of differentiation at nuclear intron alleles were congruent with those of mtDNA, and the two species also differed in body size and shape. An ancient sea channel between the Tiburon Peninsula and mainland Haiti was likely a dispersal barrier that led to allopatric divergence, a hypothesis supported by our estimates of divergence times. Our results support the recognition of two Palm-Tanager species, confirming P. poliocephalus as Haiti’s only endemic bird species and underscoring the need to protect the Tiburon Peninsula’s single primary forest reserve.

A winter distribution model for Bicknell's Thrush (Catharus bicknelli), a conservation tool for a threatened migratory songbird.

Conservation planning and implementation require identifying pertinent habitats and locations where protection and management may improve viability of targeted species. The winter range of Bicknell’s Thrush (Catharus bicknelli), a threatened Nearctic-Neotropical migratory songbird, is restricted to the Greater Antilles. We analyzed winter records from the mid-1970s to 2009 to quantitatively evaluate winter distribution and habitat selection. Additionally, we conducted targeted surveys in Jamaica (n = 433), Cuba (n = 363), Dominican Republic (n = 1,000), Haiti (n = 131) and Puerto Rico (n = 242) yielding 179 sites with thrush presence. We modeled Bicknell’s Thrush winter habitat selection and distribution in the Greater Antilles in Maxent version 3.3.1. using environmental predictors represented in 30 arc second study area rasters. These included nine landform, land cover and climatic variables that were thought a priori to have potentially high predictive power. We used the average training gain from ten model runs to select the best subset of predictors. Total winter precipitation, aspect and land cover, particularly broadleaf forests, emerged as important variables. A five-variable model that contained land cover, winter precipitation, aspect, slope, and elevation was the most parsimonious and not significantly different than the models with more variables. We used the best fitting model to depict potential winter habitat. Using the 10 percentile threshold (>0.25), we estimated winter habitat to cover 33,170 km2, nearly 10% of the study area. The Dominican Republic contained half of all potential habitat (51%), followed by Cuba (15.1%), Jamaica (13.5%), Haiti (10.6%), and Puerto Rico (9.9%). Nearly one-third of the range was found to be in protected areas. By providing the first detailed predictive map of Bicknell’s Thrush winter distribution, our study provides a useful tool to prioritize and direct conservation planning for this and other wet, broadleaf forest specialists in the Greater Antilles.

PREDATION OF A WINTERING MIGRATORY SONGBIRD BY INTRODUCED RATS: CAN NOCTURNAL ROOSTING BEHAVIOR SERVE AS PREDATOR AVOIDANCE?

Abstract. Many studies have demonstrated the deleterious effects of introduced predators on resident populations of island birds, but few have quantified their effect on the survival and space-use behavior of migratory species. We used radio telemetry to investigate the winter survival and roosting patterns of Bicknells Thrush (Catharus bicknelli) at two sites in the Dominican Republic. Depredation by introduced rats was the only cause of mortality among 53 radio-tagged individuals monitored between January and March over multiple years; five (9%) marked individuals were depredated. Predator trapping revealed the presence of both the black rat (Rattus rattus) and Norway rat (R. norvegicus) and that the density of rats was higher in broadleaf cloud forest than in nearby pine forest. Some thrushes that used cloud forest exclusively during the day roosted at night in adjacent pine habitat. We suggest that introduced rats exert predation pressure on wintering Bicknells Thrush in the Dominican Republic and that nocturnal arboreal rat predation could influence the thrushs space-use strategies.

SITE-SPECIFIC VARIATION IN FOOD RESOURCES, SEX RATIOS, AND BODY CONDITION OF AN OVERWINTERING MIGRANT SONGBIRD

ABSTRACT. Territorial social behavior of wintering Nearctic—Neotropic migrant songbirds places males and females in direct conflict over access to winter space and resources. Outcomes of this intersexual competition can vary by species and habitat, but information has been collected for only a small subset of migrant species. We investigated the available food resources, sex ratios, and body condition of territorial Bicknells Thrushes (Catharus bicknelli) wintering in the Dominican Republic between 1999 and 2008 at two ecologically distinct wet-forest sites, one in high-elevation cloud forest and the other in mid-elevation rainforest. Arthropod abundance was greater in cloud forest habitat, which was occupied by proportionally more males, the larger-bodied sex (74% male). By contrast, both sexes occurred at parity in rainforest habitat (53% male), where soft-bodied fruit was the predominant dietary resource. Body condition of cloud forest males was comparable to that of rainforest males, but cloud forest females were in poorer body condition than rainforest females. Females at the cloud forest site may face a greater likelihood of agonistic interactions with larger-bodied males and the thermoregulatory demands of roosting in colder night temperatures (0–12°C). We suggest that there are sex-specific advantages of wintering in these two habitats and that both are critical to supporting the full demographic structure of Bicknells Thrush populations. Rainforest habitats, which are highly vulnerable to agricultural development in the Dominican Republic, may be particularly important to female survival during the winter period.

SEX AND AGE RATIOS OF BICKNELL'S THRUSH WINTERING IN HISPANIOLA

Abstract We investigated sex and age ratios of wintering Bicknells Thrush (Catharus bicknelli) across a geographic gradient of sites on Hispaniola. The island-wide proportion male was 0.64 (n  =  127), which is comparable to the known male bias in breeding areas. The proportion male varied geographically on Hispaniola, suggesting some level of habitat segregation. Male-biased ratios occurred at two sites whereas sex ratios at five sites did not differ from parity. The island-wide proportion adult was 0.72 and age ratios were significantly adult-biased at two sites. We assessed vegetative structure at all sites and the proportion of male thrushes increased significantly with density of understory vegetation. Age ratios were not associated with vegetation characteristics. Neither sex nor age ratios varied significantly with elevation. Our data suggest the possibility of sexual habitat segregation with males preferentially occupying cloud forest sites characterized by a thick understory of vines and saplings occurring at densities >10,000 stems/ha.

Energy Return on Investment (EROI), Liquid Fuel Production, and Consequences for Wildlife

Current liquid-fuel supplies in the United States are derived primarily from relatively inexpensive fossil fuels. The low cost and widespread availability of petroleum has, over the last 150 years, facilitated enormous growth in the U.S. and global economies, in their respective human populations and resource consumption, and in their attendant impacts on ecosystems worldwide. Concerns are growing, however, as to whether alternative fuel sources can fill the void left by future declines in the supply of this inexpensive and energy-rich resource, concepts expressed in phrases such as “Peak Oil,” “end of cheap oil,” and “second half of the age of oil.”