Northeastern Naturalist 77 L. Nolfo-Clements 2018 Vol. 25, Special Issue 9 Mammals of the Boston Harbor Islands: Permanent and Ephemeral Residents Lauren Nolfo-Clements1,* Abstract - I monitored the mammals of the Boston Harbor Islands through various means from 2010 to 2016 in order to create a baseline inventory of species and assess the possibility of additional, focused, research. I employed camera trapping, visitor sightings, and animal-sign surveys to assess the presence of medium- and large-sized mammals. Small mammals were more closely monitored on 2 of the islands—Bumpkin and Peddocks— using short-interval mark–recapture trapping. Small mammals appear to be permanent residents on the islands and undergo significant population fluctuations, which is unusual for insular populations. Medium and large species likely move between islands and the mainland. Larger species, i.e. Canis latrans (Coyote) and Odocoileus virginianus (Whitetailed Deer), have been observed with offspring on some of the islands, while medium-sized mammals sighted were single adults. These islands offer a unique situation in which to study insular populations of mammals because the presence of larger animals varies while smaller species cannot move freely between islands or to the mainland. Introduction While numerous studies have focused on insular mammals, very few have focused on near-shore urban archipelagos. Most of these studies focus on the evolution, biogeography, extinction, and/or divergence of insular mammals (Alcover et al. 1998, Lawlor 1986, van der Geer et al. 2011). Island mammals are often isolated and are unable to move freely between individual islands and/or to the mainland; thus they tend to exhibit traits associated with genetic isolation and adaption to an insular environment. The so-called “island rule” postulates that larger animals exhibit dwarfism and smaller animals exhibit gigantism on islands (Foster 1964, Lomolino et al. 2013). In addition to morphological changes, insular mammals may also exhibit other unique characteristics when compared to their mainland counterparts including changes to social structure, ranging behaviors, animal density, and population fluctuations (Adler and Levins 1994). The Boston Harbor Islands (BHI) differ from many other marine archipelagoes in that some of the islands are close enough to the mainland for medium and large animals to swim between them. A few of the islands are within 0.5 km of the mainland, and Bumpkin Island is sometimes attached to the mainland via a land bridge during low tide. Portions of the harbor may freeze for short periods, allowing mammals to walk between islands and between the islands and mainland, as sometimes featured on the local news. 1Suffolk University, Biology Department, Boston, MA 02108; lnolfoclements@suffolk.edu. Manuscript Editor: James Cardoza Boston Harbor Islands National Recreation Area: Overview of Recent Research 2018 Northeastern Naturalist 25(Special Issue 9):77–89 Northeastern Naturalist L. Nolfo-Clements 2018 78 Vol. 25, Special Issue 9 Trocki et al. (2007) undertook an inventory of wildlife on the BHI, which included non-volant mammals. They utilized cubby boxes with track plates in addition to 2 wildlife cameras. They detected 10 species of mammals, only 1 of which was not noted in this study: Felis catus L. (Domestic Cat). To my knowledge, this is the first study to describe a marine island ecosystem in which larger species may move freely onto and off of islands while smaller species remain in place. This situation may have impacts not only on small-mammal species’ population dynamics but also the vegetation and insect communities of BHI. Methods The BHI are a group of 34 islands and peninsulas to the east of the city of Boston in Massachusetts Bay. They range in size from about 0.1 ha to 104 ha and encompass a wide variety of habitats from nearly bare rock to hardwood forest. For a full description of the vegetative communities of BHI, see Elliman (2005). The climate is temperate with distinct seasons; annual precipitation is about 1500 mm with no distinct wet or dry season (www.weather.gov). I documented presence/absence of mammal species through direct observations of individual animals, photographic evidence from wildlife cameras, and through the observation of animal sign including scat, tracks, or skeletal remains on 12 of the islands (Fig. 1). Some of the remains were near the shoreline, but most were Figure 1. Map of the Boston Harbor Islands indicating locations of mammal occurrences recorded from 2010–2016. CT = camera trapping, OB = observations, TR = transects, NA= no data available. Map courtesy of Mark. D. Clements. Northeastern Naturalist 79 L. Nolfo-Clements 2018 Vol. 25, Special Issue 9 further inland. I ran systematic transects for animal sign a single time on Grape Island during the winter 2012 and deployed wildlife cameras on Bumpkin, Grape, Long, Lovells, Peddocks, Spectacle, and Thompson islands at various times between 2011 and 2016. Due to the small number of camera units available for this study (4), I made an effort to set the cameras along wildlife trails and adjacent to areas with high mammal- activity, as indicated primarily by an abundance of tracks. I used Camtrackker game cameras [Digital Ranger; Watkinsville, GA] set to take pictures in response to motion. The cameras were typically set out and checked by interns and were not arranged in such a way as to standardize data collection. In most cases, the cameras were checked every 2–3 months for battery changes, picture downloading, and, frequently, site relocation. Cameras were deployed across seasons. I also made many incidental observations of animals and their sign, as did visitors, volunteers, and park employees. Visitors and employees were informally notified that we were keeping records of mammal observations. Records of animal presence were sent to the Natural Resource Partnerships Program Director of BHI. The animal species, island, type of sign, number of individuals, date, location, source, certainty of the sighting, and distance from the animal (if applicable) were noted for each record. Photographic evidence provided with sightings (when available) was archived in a dedicated database. I have conducted live trapping of small mammals at 2-week intervals on Peddocks Island in June and Bumpkin Island in July since 2011 and 2008, respectively. I set traps in grid patterns that covered roughly the same areas across years. I used single model LFATDG Sherman live traps baited with a mixture of peanut butter and oats and provided leaf litter as insulation. I checked traps daily. Young adult and adult animals were implanted with a passive integrated transponder tags (PIT; Biomark model TXP1485B) for individual identification. For a full description of these methods, see Nolfo-Clements and Clements (2015). Results and Discussion During the period 2011–2016, I received reports of 276 discrete mammal documentations including individual photos taken by wildlife cameras, identification of sign (tracks and scat), identification of remains, and visual identification of living animals. The majority of the documentations of mammals and their sign (261, 95%) were made on 7 of the islands: Bumpkin, Grape, Long, Lovells, Peddocks, Spectacle, and Thompson, all of which had wildlife cameras deployed on them for some period of time. I have incidental data from Calf, Georges, Great Brewster, Rainsford, and Webb islands (Fig. 1; Appendix 1). I received observations of 15 different non-volant, terrestrial, mammal species in addition to a few records of unspecified bats and seals (Table 1). The most commonly observed and widespread species were Odocoileus virginianus Zimmermann (White-tailed Deer), Canis latrans Say (Coyote), and Procyon lotor L. (Raccoon). Rattus norvegicus Berkenhout (Norway Rat), Peromyscus leucopus Rafinesque (White-footed Mouse), Microtus pennsylvanicus Ord (Meadow Vole), Urocyon Northeastern Naturalist L. Nolfo-Clements 2018 80 Vol. 25, Special Issue 9 Table 1. Mammal species presence recorded by island in the Boston Harbor 2010–2016. An asterisk (*) indicates a single sighting. Only incidental sightings were made on Calf, Georges,Great Brewster, Rainsford, and Webb islands. The areas are for the terrestrial portions of the islands and do not include intertidal zones. Island Bumpkin Grape Long Lovells Peddocks Spectacle Thompson Calf Georges Great Brewster Rainsford Webb Area (ha) 12.2 21.9 85.1 19.6 74.6 34.6 54.2 7.5 15.8 7.5 6.6 13.9 Species White-tailed Deer X X X X X X X Coyote X X X X X X Raccoon X X X X X X Norway Rat X X X X X* X White-Footed Mouse X X X X X X Meadow Vole X X X* X Gray Fox X X Red Fox X X American Mink X X X* Eastern Cottontail X X Striped Skunk X* Eastern Gray Squirrel X Virginia Opossum X* River Otter X* Woodchuck X Northeastern Naturalist 81 L. Nolfo-Clements 2018 Vol. 25, Special Issue 9 cinereoargenteus Schreber (Gray Fox), and Vulpes vulpes L. (Red Fox) were seen frequently in specific locations. Neovison vison Schreber (American Mink), Mephitis mephitis Schreber (Striped Skunk), Sciurus carolinensis Gmelin (Eastern Gray Squirrel), Ondatra zibethicus L. (Muskrat), Oryctolagus cuniculus L. (European Rabbit), Lontra canadensis Schreber (River Otter), Didelphis virginiana Kerr (Virginia Opossum), and Marmota monax L. (Woodchuck) were recorded in isolated locations and/or during discrete time intervals. White-tailed Deer White-tailed Deer (hereafter, Deer) were the most frequently noted species through direct observation, wildlife camera photographs, and sign. Observers typically only noted if a Deer was an adult or fawn, but not the sex of the individual. This frequency in observations is in part due to their ubiquity on BHI but also due to their large size and the obviousness of their retreat when startled. Deer were spotted on Bumpkin, Grape, Long, Peddocks, Spectacle, Thompson, and Webb islands. Fawns have been noted on Grape, Bumpkin, Long, and Thompson islands, but it is unknown if the young were born on the islands or swam to these locations. Deer have been recorded swimming between islands and from the mainland to islands. Coyote predation of fawns was noted on Peddocks and Bumpkin islands. Although Deer are rarely spotted in the city of Boston, they are common in suburban areas and parks just outside of the city. In Massachusetts, Deer mortality is generally low and the population in the eastern portion of the state is on the rise (McDonald et al. 2011). Due to this pattern, we can expect to see stable or increasing Deer numbers on the islands in the future. Coyotes We have documentation of Coyote dens on Bumpkin, Thompson, and Spectacle islands. The den sites were all in dense underbrush. The one on Bumpkin was dug under a concrete slab of a small, dilapidated structure, and the dens on Thompson and Spectacle were in dense vegetation away from structures. Adults and/or their sign were also observed on Peddocks, Grape, and Long islands. Examination of scat and areas around den sites revealed that Coyotes appear to be using these islands as nurseries to train their pups in predation, with Meadow Voles being the preferred prey on Bumpkin and Thompson islands (L. Nolfo-Clements, unpubl. data). This observation aligns with what is known about the diets of urban Coyotes in that they consume very little human garbage and pets, and seem to prefer wild plants and animals (Poessel et al. 2017). There was a Coyote on Spectacle Island that appeared to be a resident for at least 4 years, but that individual was recently found dead by the island caretaker. It is unclear if it had spent those years solely on Spectacle or if it had moved between islands or to the mainland. Coyotes have been observed crossing the low-tide land bridge to the mainland on Bumpkin Island and they have also been recorded traveling between locations on the frozen harbor in the winter. Urban Coyotes, specifically in the Boston area and more generally, tend to follow narrow corridors to move between patches of Northeastern Naturalist L. Nolfo-Clements 2018 82 Vol. 25, Special Issue 9 desirable habitat that are seldom frequented by people (Atwood et al. 2004, Way and Eatough 2006). BHI provides a noteworthy example of patches of semi-wild, prey-rich habitat in close proximity to an urban area. Raccoons Raccoon sightings came from Bumpkin, Long, Peddocks, Spectacle, Thompson, and Webb islands. Although Raccoons can swim, their tendency to swim in marine environments is questionable. A study of the mammals of the islands of the Gulf of Maine documented Raccoons inhabiting only islands with human-made bridges to the mainland (Crowell 1986). However, Lazell (1989) noted a Raccoon swimming over 500 m in the ocean in the vicinity of the Florida Keys. Crowell (1986) referenced a similar observation near the barrier islands off the coast of Virginia and hypothesized that Raccoons may swim in warmer ocean waters but not in colder waters. Regardless, it is also possible that Raccoons may cross the frozen harbor in the winter as do Coyotes. Alternatively, some of the Raccoons may have been purposefully introduced by people because BHI is frequented by numerous recreational boaters. The release of nuisance animals on BHI is not an impossibility, especially considering that there has never been a sighting of a juvenile Raccoon on any of the islands. Norway Rats Norway Rats were documented on many of the islands. Until the filling and capping of the garbage dump on Spectacle Island in the 1990s, that island was heavily infested with Norway Rats and probably acted as a source population for rats on other islands. Notably, Bumpkin and Grape islands do not appear to harbor Norway Rat populations despite their close proximity to the mainland; however both of these islands do have native populations of Meadow Voles and White-Footed Mice. Norway Rats are well adapted to a variety of climates, live socially in burrows, and are strong swimmers. The strong swimming abilities, burrowing habit, and omnivorous diet of the Norway Rat makes them highly adaptable; however, they also require standing fresh water to survive in certain habitats (Calhoun 1963). This requirement may make some of the islands less hospitable to Norway Rats than others. Although Norway Rats may swim freely between the harbor islands and can swim up to 1 km in the ocean (Taback et al. 2015), they are notably absent in some locations, possibly due to a lack of sufficient food resources. The presence of a freshwater source may be a deciding factor in the long-term presence and abundance of Norway Rats on an island. This hypothesis appears to fit with the distribution of Norway Rats on BHI. The islands where sightings of live Norway Rats are most prevalent—Lovells, Peddocks, and Thompson islands— all have freshwater wetlands. Other islands where Norway Rats have been occasionally noted, such as Calf and Spectacle islands, do not have such wetlands. Great Brewster Island, another location where rats were sighted, however, does support a wetland. Northeastern Naturalist 83 L. Nolfo-Clements 2018 Vol. 25, Special Issue 9 White-Footed Mice White-Footed Mice have been studied as part of a long-term monitoring project on both Bumpkin and Peddocks islands since 2008 and 2012, respectively. Due to their small size and nocturnal habit, their distribution on BHI is not certain but they have also been observed on Georges, Long, Rainsford, and Thompson islands. The results of the mouse and vole trapping on Bumpkin Island were reviewed by Nolfo-Clements and Clements (2015). The mice on these 2 islands are unusually large as predicted by the island rule (Nolfo-Clements et al. 2017). Large body-size is a strong indication that the mice on these islands are physically and genetically isolated from mainland populations. Meadow Voles The Meadow Voles on BHI appear to also be isolated on individual islands (Table 1), although they do not exhibit hallmarks of the island rule. We lack sufficient data to thoroughly compare the morphology of BHI versus mainland populations of Meadow Voles. However, we do know that the pelage of the Meadow Voles on BHI does not notably differ from those found on the mainland. Additionally, the Meadow Voles on Bumpkin Island appear to be undergoing population cycling, which is typical of microtine rodents but not insular populations (Nolfo-Clements and Clements 2015; unpubl. data). Meadow Voles have frequently been noted on Bumpkin, Grape, and Thompson islands and there is a single observation for Spectacle Island. Foxes Both Gray Foxes and Red Foxes were observed on BHI, but only adult animals were documented. We currently have no evidence that foxes are denning on the islands. Gray Foxes are well-known island inhabitants. The only other species in the genus Urocyon is U. littoralis (Baird) (Island Gray Fox), a miniature version of the Gray Fox. Island Gray Foxes occur on the 6 largest Channel Islands off the coast of southern California. The foxes are thought to have arrived on the 3 largest Channel Islands by swimming or riding on a raft of debris some 16,000 years ago, when sea levels were significantly lower (Goldstein et al. 1999). On BHI, Gray Foxes have only been observed on Grape and Webb islands. Single-sex populations of Red Foxes were introduced to Outer Brewster, Middle Brewster, Calf, and Spectacle islands in the 1960s for gull control; however, those populations were not maintained (Kadlec 1971). During our interval of observations, Red Foxes were reported on Long and Webb islands. Webb Island is a peninsula and Long Island was attached to the mainland by a bridge until recent years; hence, there is little evidence that Red Foxes have moved to the islands via swimming. There are few published accounts of insular Red Fox populations. A notable example occurs in Newfoundland; however, this population most likely arrived post-glacially via a frozen connection to the mainland about 9000 years ago (Langille et al. 2014). Red Foxes are known from other temperate islands that connect to the mainland via ice in the winter. In the St. Lawrence River, Red Foxes have Northeastern Naturalist L. Nolfo-Clements 2018 84 Vol. 25, Special Issue 9 been recorded travelling 1 km or more over ice to move between islands (Lomolino 1988). American Mink Mink were observed on Bumpkin and Grape islands. Some possible scat was also found on Great Brewster Island. Mink are generally nocturnal, solitary predators and the sexes may avoid intersexual competition through temporal separation— males tend to be nocturnal and females diurnal (Lariviere 1999, Zschille et al. 2012). Even in habitats where there are abundant wild American Mink, they are seldom seen by casual visitors due to their solitary, nocturnal habit, so it is possible that this species is present on other islands in the harbor. American Mink are semiaquatic and are typically found in areas adjacent to fresh water such as streams, rivers, wetlands, and lake shores (Lariviere 1999). There was a now-extinct mink, Neovison macrodon, Prentiss (Sea Mink), that once inhabited the coast of New England and eastern Canada. It is considered a subspecies of N. vison by some; however, it was highly specialized for the aquatic, marine niche and was significantly larger and morphologically more robust than any known subspecies of American Mink (Black et al. 1998, Mead et al. 2000, Sealfon 2007). Rabbits European Rabbits were introduced to Lovells Island in the 1940s, Bumpkin Island in the 1970s, Gallops Island probably in the 1980s, and Middle Brewster Island at some unknown time (Cardoza 1998). European Rabbits were present on Lovells, Gallops, and Middle Brewster islands in the 1990s, but were only present on Lovells and Gallops islands by the early 2000s. The rabbits on Lovells Island were implicated in contributing to the failure of a Sternula antillarum Lesson (Least Tern) nesting colony on that island in 2007 (Nolfo-Clements and Clements 2011). However, the previously burgeoning European Rabbit population had completely disappeared on Lovells Island by 2010. Currently, there are no breeding populations of European Rabbits on the islands, although a pet white rabbit was left on Lovells Island in 2012 and removed from the island by rangers at the end of the summer season. Another white rabbit was also observed on the island on 2 occasions in 2013. It appears that those rabbits had been abandoned on the islands because they were solitary and no other rabbits have been reported since 2009. Sylvilagus transitionalis Bangs (New England Cottontail) were introduced to Grape Island in 1985 and were still present on the island in the late 1990s (Cardoza 1998). The mammal survey on Grape Island in 2012 did not uncover definitive evidence of New England Cottontails, although some possible scat was photographed and 2 partial skeletons with skulls, estimated to be only ~2 y old based upon bone scatter and weathering patterns, were collected (Behrensmeyer 1978; L. Nolfo- Clements, unpubl. data). Eastern Cottontails were spotted on Long and Webb islands, which have or recent ly had a connection to the mainland via a human-made bridge or as a peninsula, respectively. Eastern Cottontails have not been observed in any other part of BHI. Northeastern Naturalist 85 L. Nolfo-Clements 2018 Vol. 25, Special Issue 9 Other mammals The smell of skunk was reported on Peddocks Island in 2010 and 2011, although no visual confirmation of the animal or its sign was ever made. Striped Skunks are surprisingly strong swimmers, although they have not been recorded swimming in a marine environment and may avoid deeper waters (Bailey 1971, Wilbur and Weidenbacher 1961). The suspected Striped Skunk may have been a nuisance animal that was transported to the island, or it may have crossed the ice when the harbor was frozen. Alternatively, the smell in at least 1 case may have come from a carcass that washed ashore, since one of the records is from an unspecified location on the island. Muskrats occur on Calf and Lovells islands and their sign is abundant in the wetland areas of those islands, as would be expected of wetland specialists with strong swimming abilities. Surprisingly, this species and its sign have not been reported from other BHI wetlands. Eastern Gray Squirrels were frequently reported on Thompson Island. This island has sufficient tree cover and, at about 54 ha, is a large enough area to support a breeding population of Easter Gray Squirrels (Rosenblatt et al. 1999). Whether the squirrels have been on the island since it was part of the mainland about 9000 years ago or if they have been more recently introduced by humans is unknown. A Virginia Opossum was found dead in a grease trap on George’s Island. This individual was probably a nuisance animal that was released on the island or perhaps a lone, intrepid, swimmer, since no other Virginia Opossums have been noted anywhere else on BHI. Much like skunks, opossums are capable swimmers (Wilbur and Weidenbacher 1961). River Otter scat was identified in the wetland on Long Island. It is unclear if the animal swam to that location or if it had crossed the bridge to the mainland at an earlier time. The Woodchuck that was observed was on Webb Island, which is actually a peninsula, and thus its occurence there did not likely involve swimming or travel over ice. Conclusions This series of observations and documentations has revealed a surprising diversity of mammals on the BHI. Although we have not undertaken methodical data collection for many of the species present, there are numerous potential studies that might elucidate the interactions and movement patterns of medium- and largesized mammals between islands and between islands and the mainland. In addition to camera-trapping studies designed to assess population densities of these larger species, radiotelemetry should be considered as a means of monitoring their movement. We are also considering the use of hair traps to facilitate the genetic analysis of mammal species and their movements because this method does not require the time and labor involved in the live capture and handling of larger wild mammals. Other studies that may be of interest include herbivore-exclusion studies to assess the impacts that the numerous White-tailed Deer on BHI may be having on the vegetation and insect communities. A more targeted analysis of the effects of Northeastern Naturalist L. Nolfo-Clements 2018 86 Vol. 25, Special Issue 9 Coyote predation on Meadow Vole populations would also be of interest to assess the role of predation in the population cycling of that species of small mammal. Acknowledgments I thank staff members from the National Park Service and the Massachusetts Department of Conservation and Recreation, as well as citizen scientists who assisted with data collection. I am especially grateful to M. Albert, S. Bass-Werner, A. Petit de Mange, and R. Vincent for all of their support with data collection and curation. Thank you to J. Cardoza and 2 anonymous reviewers whose edits and suggestions greatly improved the quality of this manuscript. 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Mammal species, island name, and type(s) of observation(s) for mammal sightings recorded on the Boston Harbor Islands 2010–2016. “Sign” refers to tracks, scat, and/or evidence of gnawing/bite marks; “remains” refers to bones and/or soft-tissue remains; “photos” refers to pictures taken by wildlife cameras; and “visual” refers to a liveanimal sighting. Species Island Observation type(s) White-tailed Deer Bumpkin Sign, visual Grape Photos, sign, visual Long Visual Peddocks Photos, sign, visual Spectacle Visual Thompson Visual Webb Visual Coyote Bumpkin Visual Grape Sign, visual Long Photos, visual Peddocks Photos, sign, visual Spectacle Photos, remains, sign, visual Thompson Sign, visual Raccoon Bumpkin Photos Long Visual Peddocks Visual Spectacle Remains, visual Thompson Photos, visual Webb Visual Norway Rat Lovells Photos, remains, sign, visual Peddocks Visual Spectacle Remains Thompson Photos, visual Calf Visual Great Brewster Visual White-Footed Mouse Bumpkin Visual Long Visual Peddocks Sign, visual Thompson Photos, visual Georges Visual Rainsford Sign Meadow Vole Bumpkin Visual Grape Visual Spectacle Visual Thompson Remains Northeastern Naturalist 89 L. Nolfo-Clements 2018 Vol. 25, Special Issue 9 Species Island Observation type(s) Gray Fox Grape Visual Webb Visual Red Fox Long Visual Webb Visual American Mink Bumpkin Visual Grape Visual Great Brewster Sign Eastern Cottontail Long Visual Webb Visual Striped Skunk Peddocks Olfactory (“smelled skunk”) Eastern Gray Squirrel Thompson Photos, visual Virginia Opossum Georges Remains River Otter Long Sign Woodchuck Webb Visual