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Chesapeake Bay most important wintering area for canvasback duck
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Common Terns (Sterna hirundo) use of a staging site in the Chesapeake Bay
In 2021, we initiated fieldwork to assess the relative importance of a staging area for Sterna hirundo (Common Tern) at a pier at the confluence of the Patuxent River and Chesapeake Bay, MD. During the post-breeding periods of 2021 through 2023, we resighted 378 banded Common Terns at this staging area, with individuals originating from 6 breeding colonies. Most banded individuals were from Poplar Island, a major nesting site 50 km north of the pier, with up to 37% of that island's annual hatch-year population observed at this staging area. Additionally, biologists have previously observed staging terns at this site, suggesting these observations do not reflect a change in the species' behavior within the region. Cumulatively, our data suggest that this habitat acts as an important staging area for the Chesapeake Bay's Common Tern population, particularly for those nesting on Poplar Island.
Mortality of unionid bivalves (Mollusca) associated with Dreissenid mussels (Dreissena polymorpha and D. bugensis) in Presque Isle Bay, Lake Erie
Two exotic species of dreissenid mussels (Dreissena polymorpha and D. bugensis) began to colonize bottom substrates in Presque Isle Bay, Lake Erie in 1990. By 1991, all native unionid (Unionidae) shells were infested by dreissenids. In 1990 and 1991, about 500 individual unionids of 15 species were collected: in 1992, 246 individuals of 12 species were collected; in 1993, 64 individuals of 6 species; in 1994, three individuals of three species; and in 1995, no unionids were found. In general, infestation indices of unionids were relatively low in 1990 and 1991, increased in 1992, and decreased in 1993. Mortality of unionids associated with infestation in the bay occurred in a shorter period of time (ca. two to three years) than has been documented in other water bodies. Observations in an area of Presque Isle not included in the present study, indicate that a small remnant population of unionids exists in the presence of heavily-colonized substrates by dreissenid mussels. Since other shallow-water areas of Lake Erie support infestation-free unionids in the presence of dreissenid mussels, it is hoped that some unionids will survive in Presque Isle Bay of Lake Erie.
Discovery of a new Kittlitz's murrelet nest: Clues to habitat selection and nest-site fidelity
On 13 June 1993, a new Kittlitz's murrelet ( Brachyramphus brevirostris ) nest was discovered near Red Mountain on the Kenai Peninsula, Alaska. The nest was on a 22° slope at about 900 m elevation with a northeast aspect, and contained a 60.2 × 40.6 mm egg that weighed 49.0 g. Downy feathers and weathered fecal material found at the nest indicated re-use from a previous year, suggesting possible nest site fidelity. The nest was located in an area scoured by winds and free of snow during early spring, suggesting that this may be an important mesoscale factor influencing selection of nesting habitat. Proximity to suitable foraging habitat, particularly sheltered bays and glacial river outflows, may affect breeding habitat choice over larger spatial scales.
Razorback sucker movements and habitat use in the San Juan River inflow, Lake Powell, Utah, 1995-1997
Seventeen subadult, hatchery-reared razorback suckers ( Xyrauchen texanus ; (x̄ = 456 mm total length) were implanted with sonic transmitters and tracked for 23 months in the lower 89.6 km of the San Juan River (San Juan arm of Lake Powell, Utah). Fish were released at 2 sites, and 9 made extensive up-and downstream movements (x = 47.8 km; contact was lost with 4, and 4 others presumably died or lost their transmitters). The San Juan arm is primarily inundated canyon; however, most fish contacts occurred in shallow coves and shoreline with thick stands of flooded salt cedar in the upper inflow area. Eight fish frequented the Piute Farms river/lake mixing zone, and at least 4 moved upstream into the San Juan River. Seven fish were found in 2 aggregations in spring (3 fish in Neskahi Bay in 1996 and 4 fish just downstream of Piute Farms in 1997), and these may have been associated with spawning activity. Continued presence of razorback suckers in the Piute Farms area and lower San Juan River suggests the San Juan inflow to Lake Powell could be used as an alternate stocking site for reintroduction efforts.
Loss of eelgrass in Casco Bay, Maine, linked to Green Crab disturbance
Over half of the Zostera marina (Eelgrass) cover disappeared from Casco Bay, ME, largely between 2012 and 2013. Eelgrass decline coincided with a population explosion of the invasive crab Carcinus maenas (European Green Crab). Green Crabs have been found to damage Eelgrass in Atlantic Canada through foraging activity, but destruction of established beds had not been documented in Maine. My objective was to determine whether loss of Eelgrass from Casco Bay was related to Green Crab disturbance. In September 2013, I transplanted Eelgrass shoots inside and outside of replicate Green Crab exclosures in a formerly vegetated area of upper Casco Bay. Following 26 d, mean survival of Eelgrass inside the exclosures was 82% and outside the exclosures was 24%. The mean plastochrone interval (time between formation of 2 successive leaves) of undamaged shoots was the same inside and outside the exclosures, and was comparable to published values from healthy Eelgrass beds in New England. Results implicate Green Crab bioturbation as a leading cause of Eelgrass loss from this system.
Distribution of native mussel (unionidae) assemblages in coastal areas of Lake Erie, Lake St. Clair, and connecting channels, twenty-five years after a dreissenid invasion
Over the past 25 years, unionid mussels in the Laurentian Great Lakes of North America have been adversely impacted by invasive dreissenid mussels, which directly (e.g., by attachment to unionid shells) and indirectly (e.g., by competing for food) cause mortality. Despite the invasion, unionids have survived in several areas in the presence of dreissenid mussels. We investigated current spatial patterns in these native mussel refuges based on surveys for unionid mussels across 48 sampling locations (141 sites) in 2011 and 2012, and documented species abundance and diversity in coastal areas of lakes St. Clair and Erie. The highest-quality assemblages of native mussels (densities, richness, and diversity) appear to be concentrated in the St. Clair delta, where abundance continues to decline, as well as in in Thompson Bay of Presque Isle in Lake Erie and in just a few coastal wetlands and drowned river-mouths in the western basin of Lake Erie. The discovery of several new refuge areas suggests that unionids have a broader distribution within the region than previously thought.
Genetic Characterization of Non-Native African Jewelfish, Hemichromis letourneuxi Sauvage 1880, in Florida
The African Jewelfish, Hemichromis letourneuxi , is an invasive, predatory cichlid fish introduced at least once to Florida. Its native range is in northern Africa. First encountered in Miami in the 1960s, it has since been found west and north within the State of Florida. It thrives in a wide range of aquatic habitats, including shallow, vegetated or rocky areas of canals, tidal creeks, rivers, and marshes. We generated mitochondrial DNA sequences from 6 Florida localities, and 1 Mexico population. The resulting tree describes recent historical relationships among populations. Nearly all Florida populations of African Jewelfish are intermixed, supporting a single invasion, with one possible exception: samples from the Tampa Bay locality are distinct and may represent a separate introduction. Samples obtained from the Mexico locality, previously identified as Hemichromis guttatus (Spotted Jewelfish), appear to be genetically identical to, and indistinguishable from the H. letourneuxi sampled in Florida localities.
San Francisco 's Golden Gate: A bridge between historically distinct coyote (Canis latrans) populations?
Although coyotes ( Canis latrans ) are well-known for their adaptability to human-modified landscapes (Riley et al. 2003), as with any medium to large-sized carnivore, they typically avoid highly urbanized areas (Crooks 2002), preferring instead to use habitat fragments linked by vegetated corridors (Tigas et al. 2002). However, recent observations of coyotes in San Francisco indicate their willingness to traverse even the most densely urbanized terrain (Rubenstein 2003). Herein we use DNA to show, in an extreme example, that an adult male coyote caught in the northern tip of the San Francisco peninsula traversed the 2-km Golden Gate Bridge, potentially linking historically distinct coyote populations. We extracted DNA from the blood of a coyote that was captured, radio-collared, and released in May 2003 in the Presidio of San Francisco, part of the Golden Gate National Recreation Area located south of the Golden Gate Bridge. This coyote apparently left the park within a week and was not subsequently located. We genotyped this individual at 14 autosomal (non-sex-linked) microsatellite loci that had previously been used to delimit 4 coyote populations in central California (Sacks et al. 2004). Laboratory methods are detailed in a previous publication (Sacks et al. 2004). By comparing this genotype to the 2 adjacent populations, the North Coastal Mountain population (beginning 20 km north of the bridge) and the South Bay Hills population (20 km south of the Bridge, just south of the city), we assigned his origin to the northern population with 97.5% probability using a Bayesian model-based approach (Pritchard et al. 2000). The population of origin was the same when all 4 central California populations were used. Next, we genotyped this male and males in the 2 adjacent populations at 2 Y-chromosome loci (MS41A, MS41B; Sundqvist et al. 2001). The genotype of this male was present in 43 of 63 males from the northern population and none of 18 males (conservatively assumed to be 1 of 18 for probability calculation) in the southern population, indicating a 92% probability of origin in the northern population based on the Y-genotype. The combined probability of assignment (Sokal and Rohlf 1995) to the northern population based on both types of marker was 99.5%, making it almost certain that this coyote came from north of the Bridge. Although it is conceivable that the coyote was transported by humans or arrived in the Presidio without having traversed the Bridge, these scenarios seem unlikely. First, the coyote had no apparent injuries and, based on tooth wear, was several years old, making it unlikely that he had been in the recent custody of a wildlife rehabilitator (a general inquiry to all known wildlife rehabilitators in the area also turned up no information). Second, he was observed in the San Francisco park at the south end of the Bridge, a likely destination for a coyote that had walked across the Bridge, but not a likely choice as a new release site for a coyote. Third, while canids are generally good swimmers, it seems implausible that a coyote could swim across the San Francisco Bay, which has extremely treacherous currents. Finally, assuming his journey was unassisted, any land route other than the Golden Gate Bridge would have required him to circumvent the San Francisco Bay–Delta Estuary and move through the South Bay Hills population (>250 km). Because no coyotes captured in the South Bay Hills population had genetic profiles indicative of a northern origin (Sacks et al. 2004), this seems especially unlikely. Coyotes were most likely absent from the peninsula north of the Bridge when the Bridge was built in 1933 and have only recently begun recolonizing the area (Hall 2000). The recent southern recolonization of this area by coyotes, their apparent willingness to cross the Bridge, and recent documentation of coyotes in more central parts of San Francisco (Rubenstein 2003) indicate the possibility of direct gene flow between north-coastal and south-coastal coyote populations, which have been historically distinct (Sacks et al. 2004). Although it has been widely recognized that human fragmentation of the landscape can impede gene flow among parts of historically continuous populations, our findings reflect an example where a human modification to the landscape may have done the opposite—namely, facilitated gene flow between historically distinct sections of a species range.
Fall diets of red-breasted merganser (Mergus serrator) and walleye (Sander vitreus) in Sandusky Bay and adjacent waters of western Lake Erie
Although published studies indicate the contrary, there is concern among many sport anglers that migrating red-breasted mergansers (Mergus serrator) and other waterbirds pose a competitive threat to sport fish species such as walleye (Sander vitreus) in Lake Erie. We quantified the diet of autumn-migrant mergansers and walleye during 1998-2000 in Sandusky Bay and adjacent waters of western Lake Erie. We hypothesized that the diets of both predators would be similar in species composition, but because of different foraging ecologies their diets would differ markedly in size of prey consumed. In addition to predator samples, we used trawl data from the same general area as an index of prey availability. We found that mergansers fed almost exclusively on fish (nine species). Gizzard shad (Dorosoma cepedianum), emerald shiner (Notropis atherinoides) and round goby (Neogobius melanostomus) were consumed in the greatest numbers, most frequently and comprised the greatest biomass. Walleye fed exclusively on fish: gizzard shad, alewife (Alosa psuedoharengus) and emerald shiner were consumed in the greatest numbers, most frequently and comprised the greatest biomass. Diet overlap between mergansers and walleye was 67% by weight and 66% by species frequency. Mean total lengths of gizzard shad, emerald shiner and round goby found in walleye stomachs exceeded those captured in trawls by 47%, on average. Mean total lengths of gizzard shad, emerald shiner and round goby were greater in walleye stomachs than in merganser stomachs. Mean total lengths of emerald shiner and round goby were less in merganser stomachs than in trawls. Our results suggest that although the diets of walleye and mergansers overlapped considerably, mergansers generally consumed smaller fish than walleye. Given the abundance and diversity of prey species available, and the transient nature of mergansers on Lake Erie during migration, we conclude that competition for food between these species is minimal.
Changes in the nesting populations of colonial waterbirds in Jamaica Bay Wildlife Refuge, New York, 1974-1998
The Jamaica Bay Wildlife Refuge (JBWR) represents the largest protected area for over 300 species of migratory and resident birds on Long Island (LI), New York, and occupies a key position along the Atlantic flyway. We identified changes in nesting populations for 18 species of colonial waterbirds in JBWR and on LI, during 1974 - 1998, to provide a basis for future wildlife management decisions in JBWR and also at nearby John F. Kennedy International Airport. None of the populations was stable over the past 25 years in JBWR or on LI. Some populations in JBWR increased (Laughing Gull L. atricilla Linnaeus, Great Black-backed Gull L. marinus Linnaeus, Forster's Tern Sterna forsteri Nuttall) while others decreased (Herring Gull Larus argentatus Coues, Snowy Egret Egretta thula Molina), but only Cattle Egrets (Bubulcus ibis Linnaeus) have disappeared from the refuge. Common Tern (S. hitundo Linnaeus), Least Tern (S. antillarum Lesson), Roseate Tern (S. dougallii Montagu), Black Skimmer (Rynchops niger Linnaeus), Black-crowned Night Heron (Nycticorax nycticorax Linnaeus) and Great Egret (Ardea alba Linnaeus) populations all increased on LI over the sampling period although the Common Tern colonies in JBWR have been declining since 1986. The continued protection of the colony sites, particularly saltmarsh islands, in JBWR will be important to the conservation efforts of many colonial waterbird populations on Long Island. The JBWR colonies may serve as a source of emigrants to other Long Island colonies, and in some cases, act as a 'sink' for birds immigrating from New Jersey and elsewhere.