Thomas P. Hodgman

Survival in an Intensively Trapped Marten Population in Maine

Marten (Martes americana) are susceptible to overharvesting, and forestry practices may compound this problem by reducing habitat quality and increasing accessibility of trappers via forest roads. From May 1989 through December 1991, we estimated ageand sex-specific survival of marten in a logged area with road access. We tested for ageand sex-specific differences in survival, combined estimates of survival with published natality rates to evaluate whether harvests were sustainable, and simulated population response to management options. Trapping accounted for 90% of all documented mortalities (n = 49) among 38 radiocollared female (26 ad, 12 juv) and 36 radio-collared male (24 ad, 12 juv) marten. Most (93%) trappingcaused mortality occurred during the first 14 days of the season, during which vulnerability of adult females to trapping was 1.45-1.75 times less (P < 0.01) than for other age-sex classes. Survival from 1 May to 15 December was higher (P = 0.03) for adult females (0.39) than adult males (0.12). Harvests of female marten were not sustainable, and shortening the trapping season from 6 to 2 weeks would be ineffective at achieving a finite rate of population change (X) _1.0. Unless immigration compensated for emigration and trappercaused mortality, we estimated that survival of females would need to nearly double to sustain the population. Access by trappers via logging roads increases the potential for declines in marten populations. Regulations to reduce trapping-caused mortality may be needed to maintain viable marten populations in landscapes with extensive forest harvesting and intensive trapping. J. WILDL. MANAGE. 58(4):593-600

Mercury in Sharp-Tailed Sparrows Breeding in Coastal Wetlands

Current levels of anthropogenic mercury (Hg) in the environment can cause harm to humans and wildlife. Well-documented negative effects on birds are described, but there is presently limited information for passerine exposure to mercury. Some investigations have used insect-eating birds as potential bioindicators of mercury exposure. However, our understanding of methlymercury (MeHg) availability to birds in coastal wetlands, tidal systems that may be especially conducive to Hg methylation, remains poor. Two species of sharp-tailed sparrow breed in coastal wetlands in eastern North America and are suitable candidate indicators for contaminants in these habitats. We measured blood Hg from breeding Saltmarsh (Ammodramus caudacutus) and Nelson’s (Ammodramus nelsoni) sharp-tailed sparrows in five Maine salt marshes to determine if these species could be used to assess the extent of MeHg availability in salt marshes. Blood Hg for both species differed among the five marshes with concordance between species and...

REDEFINING RANGE OVERLAP BETWEEN THE SHARP-TAILED SPARROWS OF COASTAL NEW ENGLAND

Abstract With the designation of Nelsons Sharp-tailed Sparrow (Ammodramus nelsoni) and Saltmarsh Sharp-tailed Sparrow (A. caudacutus) as species of high conservation priority in the northeastern United States, the need to document fully their abundance, distribution, and the extent of range overlap has become increasingly important. We surveyed saltmarshes in coastal New England for both species from 1997 to 2000. The current overlap zone extends from Parker River, Massachusetts, north to Weskeag River, Maine, which expands the previously reported range overlap of 48 km to 208 km. Among the 49 sites surveyed within the current overlap zone, both species were present at 25 sites. It is possible that the species have experienced range expansion over the last several decades, especially the Nelsons Sharp-tailed Sparrow. Our findings indicate that the nominate subspecies of the Saltmarsh Sharp-tailed Sparrow warrants the greatest conservation concern given its limited geographic range, a potentially expanding hybrid zone with A. n. subvirgatus, and the potential for habitat degradation from an oil spill associated with the urban/industrial centers of the Northeast.

CONCORDANCE BETWEEN MORPHOLOGICAL AND MOLECULAR MARKERS IN ASSESSING HYBRIDIZATION BETWEEN SHARP-TAILED SPARROWS IN NEW ENGLAND

Abstract Hybridization is pivotal in framing ideas about species concepts and has the potential to produce novel genotypes that may serve as starting points for new evolutionary trajectories. Presently, Nelson’s Sharp-tailed Sparrows (Ammodramus nelsoni subvirgatus) and Saltmarsh Sharp-tailed Sparrows (A. caudacutus caudacutus) are in contact in salt marshes of Maine, New Hampshire, and northern Massachusetts. These two species hybridize, but the extent and direction of introgression has not been determined. We assessed morphological and genetic variation of 123 sharp-tailed sparrows from 5 salt marshes in New England. We used six morphological variables, including a plumage-scoring index, and five mic-rosatellite primers to assess the extent of introgression and to determine whether there was concordance between phenotypic and genotypic variation. We identified apparent hybrids and each of the two sharp-tailed sparrow species using a plumagescoring index. In general, we found that hybrids were more similar morphologically and genetically to Saltmarsh Sharp-tailed Sparrows. The alleles of hybrids were 62% Saltmarsh and 38% Nelson’s Sharp-tailed Sparrows, supporting the asymmetrical hybridization hypothesis. Concordancia entre Marcadores Morfológicos y Moleculares al Evaluar la Hibridación entre Ammodramus nelsoni subvirgatus y A. caudacutus caudacutus en Nueva Inglaterra

Predictors of specialist avifaunal decline in coastal marshes

Coastal marshes are one of the worlds most productive ecosystems. Consequently, they have been heavily used by humans for centuries, resulting in ecosystem loss. Direct human modifications such as road crossings and ditches and climatic stressors such as sea-level rise and extreme storm events have the potential to further degrade the quantity and quality of marsh along coastlines. We used an 18-year marsh-bird database to generate population trends for 5 avian species (Rallus crepitans, Tringa semipalmata semipalmata, Ammodramus nelsonii subvirgatus, Ammodramus caudacutus, and Ammodramus maritimus) that breed almost exclusively in tidal marshes, and are potentially vulnerable to marsh degradation and loss as a result of anthropogenic change. We generated community and species trends across 3 spatial scales and explored possible drivers of the changes we observed, including marsh ditching, tidal restriction through road crossings, local rates of sea-level rise, and potential for extreme flooding events. The specialist community showed negative trends in tidally restricted marshes (-2.4% annually from 1998 to 2012) but was stable in unrestricted marshes across the same period. At the species level, we found negative population trends in 3 of the 5 specialist species, ranging from -4.2% to 9.0% annually. We suggest that tidal restriction may accelerate degradation of tidal marsh resilience to sea-level rise by limiting sediment supply necessary for marsh accretion, resulting in specialist habitat loss in tidally restricted marshes. Based on our findings, we predict a collapse of the global population of Saltmarsh Sparrows (A. caudacutus) within the next 50 years and suggest that immediate conservation action is needed to prevent extinction of this species. We also suggest mitigation actions to restore sediment supply to coastal marshes to help sustain this ecosystem into the future.

Population estimates for tidal marsh birds of high conservation concern in the northeastern USA from a design-based survey

ABSTRACT Tidal marsh loss to anthropogenic environmental impacts and climate change, particularly sea level rise, has and will continue to cause declines in tidal marsh bird populations. Distribution patterns of tidal marsh birds are generally known, yet we lack detailed knowledge of local abundance and regional population sizes, which limits our ability to develop effective conservation strategies that will mitigate the impacts of marsh loss. We designed and implemented a probabilistic sampling framework to establish a regional marsh bird monitoring program, and collected baseline information for breeding tidal marsh birds in the northeastern USA (Maine to Virginia). We sampled 1,780 locations in 2011–2012 to provide regional population estimates for 5 tidal marsh–specialist birds. We estimated that there were 151,000 Clapper Rails (Rallus crepitans; 95% CI = 90,000–212,000), 117,000 Willets (Tringa semipalmata; 95% CI = 88,000–146,000), 5,000 Nelsons Sparrows (Ammodramus nelsoni; 95% CI = 1,000–9,000), 53,000 Saltmarsh Sparrows (A. caudacutus; 95% CI = 37,000–69,000), and 230,000 Seaside Sparrows (A. maritimus; 95% CI = 174,000–286,000) in northeastern tidal marshes. Our baseline assessment can be used to identify local habitat patches important to regional populations for each species and to prioritize conservation actions in targeted areas to maximize tidal marsh bird persistence. The flexibility and probabilistic design of our sampling framework also allow for integration with other monitoring programs (e.g., the U.S. Fish and Wildlife Service Salt Marsh Integrity Program and National Park Service Vital Signs Monitoring Program) so that inferences for these species can be made at multiple spatial scales.

Divergent oviposition preferences of sister species are not driven by nest survival: the evidence for neutrality

Both adaptive and neutral trait evolution can contribute to divergence, but the relative contributions of the two remain unclear. Oviposition preference, a trait that has been demonstrated to contribute to divergence among populations, is often presumed to be an adaptive trait. Few studies explicitly test this assumption, however, and several researchers have demonstrated non-adaptive oviposition preferences in wildlife populations. In this study, we test whether adaptive divergence can explain current differences in the oviposition preferences of two sister species. In 2012 and 2013, we conducted a demographic study of sympatrically breeding populations of two sparrow species (Ammodramus caudacutus and Ammodramus nelsoni) and measured vegetation characteristics at nest and non-nest points. We found evidence for oviposition preference in both species and significant differences between the species’ preferences. The vegetation characteristics that vary between species did not predict nest survival or offspring production, however. Our results provide an example of oviposition preference at a population level that appears non-adaptive as measured by productivity. We discuss other mechanisms by which oviposition preference can be adaptive, and make a case for the role of neutral evolution in shaping the oviposition preferences of these species. If divergence in oviposition preference is at least periodically neutral, as we hypothesize, such differences could provide fodder for future adaptation or reproductive isolation among populations.

Quantifying the importance of geographic replication and representativeness when estimating demographic rates, using a coastal species as a case study

Demographic rates are rarely estimated over an entire species range, limiting empirical tests of ecological patterns and theories, and raising questions about the representativeness of studies that use data from a small part of a range. The uncertainty that results from using demographic rates from just a few sites is especially pervasive in population projections, which are critical for a wide range of questions in ecology and conservation. We developed a simple simulation to quantify how this lack of geographic representativeness can affect inferences about the global mean and variance of growth rates, which has implications for the robust design of a wide range of population studies. Using a coastal songbird, saltmarsh sparrow (Ammodramus caudacutus), as a case study, we first estimated survival, fecundity, and population growth rates at 21 sites distributed across much of their breeding range. We then subsampled this large, representative dataset according to five sampling scenarios in order to simulate a variety of geographic biases in study design. We found spatial variation in demographic rates, but no large systematic patterns. Estimating the global mean and variance of growth rates using subsets of the data suggested that at least 10-15 sites were required for reasonably unbiased estimates, highlighting how relying on demographic data from just a few sites can lead to biased results when extrapolating across a species range. Sampling at the full 21 sites, however, offered diminishing returns, raising the possibility that for some species accepting some geographical bias in sampling can still allow for robust range-wide inferences. The sub-sampling approach presented here, while conceptually simple, could be used with both new and existing data to encourage efficiency in the design of long-term or large-scale ecological studies. This article is protected by copyright. All rights reserved.

Habitat selection, nest survival, and nest predators of Rusty Blackbirds in northern New England, USA

ABSTRACT Rusty Blackbird (Euphagus carolinus) populations have plummeted since the mid-20th century. Recent research in New England, USA, suggests that an ecological trap, created through timber harvesting on the breeding grounds, may be responsible. Red squirrels (Tamiasciurus hudsonicus) were hypothesized to be the primary nest predator, but definitive identification was lacking. The potential for mast cone crops to affect Rusty Blackbird nest predation via trophic interactions also remains unexamined. Our objectives were to identify the mechanisms by which an ecological trap may be operating in New England through a multiscale analysis of Rusty Blackbird habitat selection and nest survival, as well as predator identification and quantification. We located 72 Rusty Blackbird nests in Maine and New Hampshire in 2011 and 2012, and modeled habitat selection and nest survival as a function of habitat characteristics at the nest patch (5 m) and home range (500 m) scale. We placed camera traps at 29 nests to identify nest predators, and conducted ground surveys to obtain an index of squirrel abundance each year. We found that Rusty Blackbirds selected nest patches with a high basal area of small conifers and low canopy closure. Nest survival was not reduced in harvested stands, but increased with increasing basal area. Percent cover of wetlands and young softwood stands were the best predictors of Rusty Blackbird selection at the home range scale. At the home range scale, we found that nests that were closer to a road were less successful in 2011, but not in 2012. Red squirrels were the most frequent predator of Rusty Blackbird nests in 2012, when they were abundant following a mast year in 2011. These results suggest that dense cover of small softwoods is important for habitat selection and survival of Rusty Blackbird nests, and that precommercial thinning and possibly road-building could reduce habitat quality for this species.

Fine-Scale Mapping of Coastal Plant Communities in the Northeastern USA

Salt marshes of the northeastern United States are dynamic landscapes where the tidal flooding regime creates patterns of plant zonation based on differences in elevation, salinity, and local hydrology. These patterns of zonation can change quickly due to both natural and anthropogenic stressors, making tidal marshes vulnerable to degradation and loss. We compared several remote sensing techniques to develop a tool that accurately maps high- and low-marsh zonation to use in management and conservation planning for this ecosystem in the northeast USA. We found that random forests (RF) outperformed other classifier tools when applied to the most recent National Agricultural Imagery Program (NAIP) imagery, NAIP derivatives, and elevation data between coastal Maine and Virginia, USA. We then used RF methods to classify plant zonation within a 500-m buffer around coastal marsh delineated in the National Wetland Inventory. We found mean classification accuracies of 94% for high marsh, 76% for low marsh zones, and 90% overall map accuracy. The detailed output is a 3-m resolution continuous map of tidal marsh vegetation communities and cover classes that can be used in habitat modeling of marsh-obligate species or to monitor changes in marsh plant communities over time.