Wales A. Carter

Context: Islands can be used to aid conservation efforts for rare species by providing a safe refuge. Over the past decade, islands have been used to aid in conserving New England cottontail (NEC; Sylvilagus transitionalis), by serving as a source for translocations to mainland release sites. The success of the first breeding colony island led to the initiation of Nomans Land Island National Wildlife Refuge (NWR) as a second island colony. Nomans Land Island NWR is 255 ha of wildlands uninhabited by people and managed by the United States Fish and Wildlife Service. The release of NEC on the island occurred from 2019 to 2021, with the translocation of 26 NEC. Aims: Our objectives were to monitor the initial founding NEC released on Nomans Land Island NWR by (1) estimating their home range area, (2) determining their overlap in home ranges among individuals, and (3) assessing their fine-scale resource selection. Methods: We deployed Global Positioning System radio collars on the founding NEC released in two subsequent years. We first used a continuous time movement modeling approach to estimate NEC home ranges and core-use areas. Next, we estimated NEC resource selection with a used–available framework. Environmental layers included habitat classifications and normalized difference vegetation index values derived from aerial imagery. Key results: We found high amounts of variability among individuals in both their home ranges and resources selected, with individual-level resource selection often differing from population-level selection. We suspect their home ranges were initially larger than what has been estimated for mainland NEC because the island was uninhabited by rabbits prior to the release of NEC. Their average home range decreased the second year, which was likely to be a result of the increased density of NEC on the island. Conclusions: The founding NEC used a wide variety of different vegetation cover types on the island, which indicates that they will likely populate the entire island. Monitoring translocated animals is key in determining their ability to establish self-sustaining populations. Implications: Islands have played an integral role in NEC conservation and there are plans to increase the number of breeding colony islands. Breeding colony islands also could be used to aid in the conservation of other imperiled, small mammals.

Herbivores are challenged when selecting a diet because many plants have limited nutritional value and some use defenses to avoid being eaten. Understanding diet selection of herbivores in most landscapes also involves choices between native versus nonnative plant species which, in turn, informs management actions to conserve the species. The New England Cottontail, Sylvilagus transitionalis (Bangs 1895)—a species on the decline—is the focus of a large conservation consortium. We conducted microhistological analyses of field collected fecal samples and field surveys of plant species available to determine winter diet of New England cottontails on Patience Island, Rhode Island. Energy density (total nitrogen, crude fat, energy, neutral detergent fiber, acid detergent fiber, ash, and total phenolics) was measured for each of the available plants. A used-available framework was used to determine the selection of each species identified in their feces and how this related to the measured nutritionally relevant constituents. We hypothesized that New England cottontails would select plant species with higher protein and energy values and select native versus nonnative plant species. Unexpectedly, New England cottontails did not select plants with higher protein or energy content but rather plants with higher phenolic and ash levels. In addition, New England cottontails strongly selected native plant species. Our results support previous research that New England cottontails are generalist herbivores, but that plant defenses and whether the plants are native play a role in diet selection.

Islands have a long history in species conservation, as they often have fewer predators and competitors than mainland sites. In some instances, islands have been used as breeding colonies to support mainland translocations. In the past decade, 2 islands in New England have been selected to establish island breeding colonies of New England cottontail ( Sylvilagus transitionalis ), a species of conservation concern. The 2 islands, Patience Island and Nomans Land Island National Wildlife Refuge (NWR), were initiated in 2012 and 2019, respectively. Our main objective was to monitor the genetic diversity and population size response of the removal of New England cottontails from Patience Island for translocation to mainland sites. This allowed us to test theoretical predictions about the species' change in genetic diversity over time on an island system. As expected, the mitochondrial DNA haplotype diversity of New England cottontail decreased at a faster rate than their nuclear DNA heterozygosity, the latter remaining stable for over a decade. We also radio‐collared founders released on both islands to estimate their individual survival, which decreased as additional founders were released on Patience Island. We tested the influence of outcrossing parents from different populations on the survival of their released offspring on Patience Island, which had similar survival as offspring with parents from the same population. The survival of Nomans Land Island NWR founders was higher than that of Patience Island founders, likely because of the lack of mammalian predators on Nomans Land Island NWR. Islands have played a critical role in supporting New England cottontail conservation and, in the right circumstances, islands could be used to support the conservation of other lagomorphs of conservation concern. However, careful consideration is needed before an animal is introduced to an island to reduce the possible negative impacts to the island's fauna and flora and maximize the potential success of the island population in supporting the focal species' conservation.

Ecologically relevant factors such as exercise and diet quality can directly influence how multifaceted physiological systems work; however, little is known about how such factors directly and interactively affect key components of the antioxidant system in multiple tissues of migratory songbirds. We tested 3 main hypotheses across three tissues in European starlings fed diets with more or less antioxidants (anthocyanins) and long‐chain omega‐6 polyunsaturated fats (18:2n6) while being flight‐trained in a wind tunnel. Stimulatory effect of flight : flight‐training stimulated the antioxidant system in that 1) plasma oxidative damage (dROMs) was reduced during a given acute flight, and contrary to our predictions, 2) antioxidant capacity (OXY or ORAC) and oxidative damage in plasma (dROMs), flight‐muscle, and liver (LPO) of flight‐trained birds were similar to that of untrained birds (i.e. not flown in a wind tunnel). Flight‐trained birds that expended more energy per unit time (kJ min ⁻¹ ) during their longest, final flight decreased antioxidant capacity (OXY) the most during the final flight. Dietary fat quality effect: contrary to our predictions, dietary 18:2n‐6 did not influence oxidative status even after flight training. Dietary antioxidant effect : flight‐trained birds supplemented with dietary anthocyanins did not have higher antioxidant capacity in plasma (OXY), or liver and flight‐muscle (ORAC) compared to untrained birds. Counterintuitively, oxidative damage (dROMs) was higher in flight‐trained supplemented birds compared to unsupplemented birds after an acute flight. In sum, the antioxidant system of songbirds flexibly responded to changes in availability of dietary antioxidants as well as increased flight time and effort, and such condition‐dependent, individual‐level, tissue‐specific responses to the oxidative costs of long‐duration flights apparently requires recovery periods for maintaining oxidative balance during migration.

Translocations are an established element of restoration plans for threatened species, but success in establishing new populations is often limited, highlighting the need for careful evaluation of translocation efforts. Variation among individuals may contribute to poorly placed translocations, particularly when there is variation in the spatial ecology of target species. As a test of this we investigated the spatial ecology of imperiled New England cottontail ( Sylvilagus transitionalis (Bangs, 1895)) in Rhode Island, USA. We combined telemetry data with remotely-sensed vegetation data to evaluate the home ranges, resource selection, and survival of translocated cottontails at three sites, including one where we also tracked resident cottontails. Despite instances of alignment among individuals, we found a wide span of home range estimates and high individual variability on resource selection. Both of these results suggest that population-level inferences of translocated individuals may fail to capture important aspects of animal ecology at the individual level. Further, we found lower survival compared to residents at one of our sites and literature values for other resident populations. Our results suggest that there are benefits to considering variation among individuals when designing management plans to support translocations.

Ecologically-relevant factors such as exercise and diet quality can directly influence how multifaceted physiological systems work; however, little is known about how such factors directly and interactively affect key components of the antioxidant system in multiple tissues of migratory songbirds. We tested 3 main hypotheses across three tissues in European Starlings fed diets with more or less antioxidants (anthocyanins) and long-chain polyunsaturated fats (18:2n6) while being flight-trained in a wind tunnel. Stimulatory effect of flight: Flight-training stimulated the antioxidant system in that a) plasma oxidative damage was reduced during a given acute flight, and b) antioxidant capacity and oxidative damage in plasma and tissues of flight-trained birds were similar to that of untrained birds. Flight-trained birds that expended more energy per unit time (kJ/min) during their longest, final flight decreased the non-enzymatic component of their antioxidant system the most during the final flight. Dietary antioxidant effect: Flight-trained birds that consumed more dietary anthocyanins had similar antioxidant capacity in liver and flight-muscle compared to untrained birds, and oxidative damage was prevented in the flight-muscle and reduced in the liver of flight-trained birds compared to untrained birds. Dietary fat quality effect: Contrary to our predictions, dietary 18:2n-6 did not influence oxidative status even after flight training. We found limited evidence that circulating and tissue-level oxidative capacity and damage were tightly regulated in flight-trained starlings, in contrast to the precise regulation on gene expression and enzyme activity that were observed in companion studies. In sum, the antioxidant system of songbirds flexibly responded to changes in availability of dietary antioxidants as well as increased flight time and effort, and such condition-dependent, individual-level, tissue-specific responses to the oxidative costs of long-duration flights apparently requires recovery periods for maintaining oxidative balance during migration.

Migration is an energetically challenging and risky life history stage for many animals, but could be supported by dietary choices en route, which may create opportunities to improve body and physiological condition. However, proposed benefits of diet shifts, such as between seasonally available invertebrates and fruits, have received limited investigation in free-living animals. We quantified diet composition and magnitude of autumn diet shifts over two time periods in two closely-related species of migratory songbirds on stopover in the northeastern U.S. (Swainson’s thrush [Catharus ustulatus], long-distance migrant, N = 83; hermit thrush [C. guttatus], short-distance migrant, N = 79) and used piecewise structural equation models to evaluate the relationships among (1) migration timing, (2) dietary behavior, and (3) morphometric and physiological condition indices. Tissue isotope composition indicated that both species shifted towards greater fruit consumption. Larger shifts in recent weeks corresponded to higher body condition in Swainson’s, but not hermit thrushes, and condition was more heavily influenced by capture date in Swainson’s thrushes. Presence of “high-antioxidant” fruits in fecal samples was unrelated to condition in Swainson’s thrushes and negatively related to multiple condition indices in hermit thrushes, possibly indicating the value of fruits during migration is related more to their energy and/or macronutrient content than antioxidant content. Our results suggest that increased frugivory during autumn migration can support condition, but those benefits might depend on migration strategy: a longer-distance, more capital-dependent migration strategy could require stricter regulation of body condition aided by increased fruit consumption.

Invasive species are widely implicated in the decline of songbird populations, potentially via indirect effects such as the restructuring of ecological communities by non-native plants. We used stable isotope analysis to investigate whether ground-foraging, generalist insectivore ovenbirds ( Seiurus aurocapilla (Linnaeus, 1766)) shifted diets following invasion by a non-native shrub, Japanese barberry ( Berberis thunbergii DC.), in a temperate woodland system in New York, USA where barberry was previously linked to trophic downgrading in the leaf litter arthropod community. Assimilated ovenbird diets were primarily composed of predatory invertebrates followed by sucking herbivores, chewing herbivores, and detritivores. The only notable changes in assimilated ovenbird diets were a modest 14.7% decrease in chewing herbivore contributions and a minor 7.0% increase in sucking herbivore contributions in forest patches with high barberry densities. Our results indicate that the effects of non-native plants on connections between higher trophic levels are context-dependent, and comparisons with other studies suggest that community complexity and time since introduction are key contextual differences that affect the outcome of an invasion. Our results may reflect compensatory shifts in individual foraging effort by ovenbirds, but, in combination with our previous research, provide little evidence that barberry affects ovenbird condition and therefore downstream outcomes.

Ongoing declines in the imperiled New England cottontail Sylvilagus transitionalis have coincided with the introduction and expansion of the closely related eastern cottontail Sylvilagus floridanus. These paired population trends have led to the inference of competition between the two species. Competition between native and introduced species has often involved overlapping use of food resources, but limited effort has been spent to analyze the diets of New England cottontail and eastern cottontail and to evaluate the potential for resource competition. We used microhistologic analysis of fecal pellets to assess the winter diets of both species and we compared diet composition with available plant communities to evaluate their preferences for dietary items across southern New England and southeastern New York. We found no differences in diets between New England cottontail and eastern cottontail, although diets did differ between regions within the study area. Diet preferences also were consistent between the species and largely excluded nonnative plant genera. Our results demonstrate that these species are generalist herbivores and that there is high potential for competition for food resources in the winter between them, although the present lack of diet partitioning may indicate the presence of other factors limiting competition. This study highlights the need for careful evaluation of interactions between native and nonnative species, a prerequisite for developing conservation plans that appropriately account for interspecific competition.