Numbers Of Gulls Research Articles

History of monitoring the endangered ivory gull in the Canadian Arctic

The ivory gull ( Pagophila eburnea Phipps 1774) is a rare seabird found in the Canadian High Arctic. The Seymour Island Migratory Bird Sanctuary has supported the core colony for ivory gull research since the 1970s, but by the 2000s, survey work was extended across the species’ range in Nunavut, prompted by growing Indigenous concerns of population declines, which led to regular monitoring of colonies. We found marked declines in numbers of ivory gulls since the 1980s, especially in the southern part of the range, leading the Canadian Committee on the Status of Endangered Wildlife in Canada to recommend uplisting ivory gulls to Endangered under Canada’s Species At Risk Act, which the federal government did in 2009. This resulted in the development of a national Recovery Strategy that outlined research and monitoring needs. Canadian results prompted international concern and led to coordinated, international research and monitoring on this iconic Arctic species, which collectively suggested worldwide declines in the species’ numbers. Despite our efforts, the future of monitoring, and indeed of ivory gulls in Canada, remains unclear.

Investigation of an unusual cluster of illness among staff at a wildlife rescue centre

Abstract When two previously fit and well staff from a wildlife rescue centre were hospitalised in early September 2018 with severe pneumonia and meningitis symptoms, the Health Protection Team began an investigation. Possible diagnoses included influenza and legionella, although it was not flu season, and initial testing proved negative. There were reports of other staff illness over the preceding weeks. The centre had accepted a wide range species over the Summer, including high numbers of gulls and pigeons, and an outbreak of psittacosis was suspected; the patients responded rapidly to doxycycline. An incident management team was rapidly convened to investigate and determine control measures. A testing algorithm was developed: including for Influenza A&B, Urine legionella & pneumococcal antigen; reference laboratory serology testing and real-time PCR for Chlamydia.psittaci; and pan-corona viruses. Case finding was conducted by telephone interviews and a select-survey of all 55 staff gained 46 responses. A series of site visits examined working practices at the site. Avian and environmental sampling was undertaken. A total of 22 staff met the agreed case definition for psittacosis, five of whom were later confirmed. Clinical features ranged from mild to severe. The onset dates of illness ranged from July to September. There was no evidence of person-to-person transmission. Analysis did not show a clear correlation between PPE use and illness. Clinical, microbiological, environmental, veterinary, and epidemiological evidence indicated zoonotic transmission of psittacosis. Variable compliance with PPE, hygiene when handling birds, and disinfection had likely contributed via aerosolization of dust. This was likely exacerbated by very high bird stocks and unusually warm weather conditions. Comprehensive recommendations were made to reduce the chances of future outbreaks, which are generalisable to other countries. Key messages • This was one of the largest clusters of human psittacosis described in a workplace in England. • Biosecurity in animal rescue centres is crucial to limit the chance of psittacosis and other zoonoses.

Using a visual deterrent to reduce seabird interactions with gillnets

Bycatch is one of the main threats to seabird conservation. In Portugal, there are alarming estimates of seabirds bycaught per year in bottom gillnet fisheries, which get entangled during fishing operations, when the gear is close to the surface. In this study, a visual deterrent (scarybird) was tested in a fishing vessel operating bottom gillnets near and within Berlengas Islands SPA (Special Protection Area). Trials were conducted between 2019 and 2020, with 18 control and experimental fishing trips monitored by a trained observer. The scarybird proved to be an effective bird deterrent measure, affecting both the numbers and distribution of seabirds and keeping a large portion of birds away from the vessel during fishing operations, making them potentially less vulnerable to bycatch. The deterrent device was more effective in the closest area to the vessel (0–20 m) where there was a significant reduction in the number of gulls (Larus michahellis/fuscus, −56 %) and northern gannets (Morus bassanus, −72 %) close to the vessel, by comparison to control fishing trips. The use of this aerial deterrent device had no impact on the fishery's target catches and revenue, which contributed to a good acceptance by fishermen. This simple and “easy to implement” deterrent device has potential to be further tested as a bycatch mitigation measure in bottom gillnets but also in other gears, whenever interactions with birds occur mainly close to the surface.

Evaluation of the Effect of Pb Pollution on Avian Influenza Virus-Specific Antibody Production in Black-Headed Gulls (Chroicocephalus ridibundus).

Lead (Pb), an environmental pollutant, has been widely reported to have contaminated mammals, including humans and birds. This study focuses on the effects of Pb pollution on avian influenza virus (AIV) antibody production. A total of 170 black-headed gulls (Chroicocephalus ridibundus) were captured in Tokyo Bay (TBP) from January 2019 to April 2020 and in Mikawa Bay (MBP) from November 2019 to April 2021. The gulls were weighed, subjected to blood sampling, and released with a ring band on their tarsus. The samples were used to measure blood Pb levels (BLL) and AIV-specific antibodies. The BLL were compared using the Wilcoxon two-sample test between the period when black-headed gulls arrived and the wintering period, defined by the number of gulls counted in each area. A significant increase was found in the TBP. A decrease in BLL significantly increased antibody titer during wintering in TBP and MBP. Pb pollution had a negative effect on the production of AIV antibodies. These findings suggest that wild birds that were contaminated by Pb in the environment may facilitate the spread of zoonotic diseases, further increasing the possibility that environmental pollutants may threaten human health.

Patterns in avian reproduction in the Prudhoe Bay Oilfield, Alaska, 2003–2019

The Arctic Coastal Plain is one of the most important avian breeding grounds in the world; however, many species are in decline. Arctic‐breeding birds contend with short breeding seasons, harsh climatic conditions, and now, rapidly changing, variable, and unpredictable environmental conditions caused by climate change. Additionally, those breeding in industrial areas may be impacted by human activities. It is difficult to separate the impacts of industrial development and climate change; however, long‐term datasets can help show patterns over time. We evaluated factors influencing reproductive parameters of breeding birds at Prudhoe Bay, Alaska, 2003–2019, by monitoring 1265 shorebird nests, 378 passerine nests, and 231 waterfowl nests. We found that nest survival decreased significantly nearer high‐use infrastructure for all guilds. Temporally, passerine nest survival declined across the 17 years of the study, while there was no significant evidence of change in their nest density. Shorebird nest survival did not vary significantly across years, nor did nest density. Waterfowl nest density increased over the course of the study, but we could not estimate nest survival in all years. Egg predator populations varied across time; numbers of gulls and ravens increased in the oilfields 2003–2019, while Arctic fox decreased, and jaeger numbers did not vary significantly. Long‐term datasets are rare in the Arctic, but they are crucial for understanding impacts to breeding birds from both climate change and increasing anthropogenic activities. We show that nest survival was lower for birds nesting closer to high‐use infrastructure in Arctic Alaska, which was not detected in earlier, shorter‐term studies. Additionally, we show that Lapland longspur nest survival decreased across time, in concert with continent‐wide declines in many passerine species. The urgency to understand these relationships cannot be expressed strongly enough, given change is continuing to happen and the potential impacts are large.

Year-round use of anthropogenic food sources in human modified landscapes by adult and young Kelp Gulls

Predictable anthropogenic food subsidies attract species with generalist and opportunistic feeding habits, often resulting in conflicts with human populations. We assessed the spatio-temporal distribution and abundance of Kelp Gulls (Larus dominicanus) during the annual cycle at anthropogenic food sources located along 70 km of urban and agricultural-livestock landscapes in the lower Chubut River valley, Argentina. We quantified the seasonal abundance of adult and young Kelp Gulls through monthly counts from July 2021 to June 2022 at six identified anthropogenic food sources, complemented with strip transect sampling along cultivated land and cattle grazing areas. In addition, we analysed the differential use of waste types by adult and young Kelp Gulls at a mixed livestock waste dump where different food remains (cattle remains, poultry remains and urban waste) are disposed in independent pits. The total number of Kelp Gulls counted each month along the river valley was variable, with a mean number of 2585 ± 822.7 individuals (range = 276 in December and 8958 in June). The highest gull abundance was recorded at a pig farm (mean = 1784.5 ± 640.1 individuals). The transect survey showed a relatively low use by gulls of the cultivated land and cattle grazing areas, with a mean of 29.7 ± 11.2 individuals recorded per survey (range = 0–96). Kelp Gull abundance patterns recorded in the river valley throughout the annual cycle evidenced a contrasting seasonal use of anthropogenic food sources between the breeding and non-breeding seasons, being clearly less abundant during the former, when gulls move to their main breeding grounds and adjacent marine habitats in coastal Chubut. At the mixed livestock waste dump, Kelp Gull numbers varied among the three waste patches, with higher numbers and a significantly higher proportion of adults at the cattle remains pit. This study shows the high trophic plasticity of Kelp Gulls and their use of alternative foraging habitats. Further monitoring and evaluations of the use by Kelp Gulls of predictable anthropogenic food sources along the Chubut River valley, particularly those related to the growing livestock production, are needed to support management decisions.

Investigating nocturnal UAS treatments in an applied context to prevent gulls from nesting on rooftops

AbstractRing‐billed (Larus delawarensis) and herring (L. argentatus) gulls are numerous and widespread in North America. These gulls rank among the top 9 species for risk of bird‐aircraft collisions (hereafter strikes). The ubiquitous presence of gulls in urban coastal environments, including rooftop nesting behavior, are factors impacting strike risk. Our purpose was to assess gull response to a small uncrewed aircraft system (UAS) in hazing flights at night during the nest‐building phase. We hypothesized that nocturnal UAS operation, like nocturnal predator disturbance, might reduce gull numbers and, thus, strike risk to aircraft. In spring 2021, we conducted UAS treatments over target roofs at least once every hour from 2000 until 0200, weather permitting, for 15 min and over a 14‐day period for each site. The UAS flew directly above (~4 m) and then descended (~4 m/s) within 1 m of loafing gulls. No gulls interacted with the UAS and most flushed within 6 minutes. Generally, the first treatment of a night dispersed all gulls (min–max = 1–130 individuals) from the target roof for an extended period. Our operations were often grounded because of weather and our gull response data were limited because of few individuals present. We discuss our observations with particular attention to feasibility and possible implications such as shifting birds to other sites which, potentially, could be counterproductive for management.

Managing conflict between nesting common terns and herring gulls

Context Due to the frequent depredation of eggs and chicks by herring gulls (Larus argentatus), numerous approaches to reduce their impact on tern colonies have been tested by wildlife managers. Previous studies have shown that the use of overhead lines presents a promising method to prevent gull nesting in tern colonies, but little work has evaluated if this approach is suitable for excluding both nesting and non-nesting gulls. Aims The goal of this study was to explore the efficacy of a preventative approach, overhead lines, versus a more widely practiced lethal approach, shooting and trapping. Specifically, we aimed to determine if methods differ in their abilities to deter both gull nesting and presence within treatment areas and identify impacts on common tern (Sterna hirundo) nesting within treatment areas. Methods We applied separate management strategies to two common tern colonies. In one colony, we removed herring gulls via shooting followed by trapping and nest removal, and in the other colony, we erected overhead lines with subsequent trapping at nests established in the treatment area. Key results Gulls appeared to adapt quickly to shooting efforts, limiting efficacy and resulting in no significant change in abundance from pre-treatment levels (P = 0.981). However, gull use of both the colony and surrounding brush declined significantly (P < 0.001) following trapping and nest removal. Meanwhile, the number of gulls in the colony area declined from a pre-treatment average of 56 to only six, following the erection of overhead lines (P < 0.001). Although six gull nests were established within the treatment area (overhead lines), they were not replaced once the parents were trapped and nests destroyed. Conclusions Tern nesting appeared to be unaffected by any of the implemented management activities. Our data suggest that overhead lines may present an alternative to lethal control when seeking to minimise the impacts of gulls on tern colonies. Implications The data presented in this manuscript can be used to guide managers in selecting actions to reduce conflict between gulls and breeding common terns. By using data-informed practices, managers can select the method best suited for their specific needs and priorities.

Impact of COVID-19 on pest birds (Silver Gulls Larus novaehollandiae) on a popular tourist island

During the COVID-19 pandemic, Rottnest Island, Western Australia, a popular tourist destination, was closed to the public for 72 days (from 25 March 2020 to 5 June), so that it could be used as a quarantine facility. Silver Gulls Larus novaehollandiae were surveyed in the main settlement area over 429 days, beginning at the commencement of the quarantine period, with a focus on a previously identified problem area, the shopping mall. These surveys allowed for the comparison of Silver Gull numbers with and without the presence of easily accessible anthropogenic food. The number of Gulls was extremely low during the quarantine period, followed by a 578% increase in the same period the following year when visitors returned. During the period of food scarcity, many of the Gulls appeared to have left the Island, which suggests that the number of pest birds on Rottnest Island can be influenced by the amount of anthropogenic food available to them.

The growth rate of Black-tailed Gull chicks is negatively related to total mercury of female parents on Kabushima (Kabu Island), Japan

The mercury (Hg) contamination at high concentrations affects the physiological state and behavior of animals, however, the effects of low Hg exposure on avian breeding success and the impact on the growth of chicks that depend on feeding from their parents are unclear. We investigated the effects of maternal Hg concentrations on breeding success in a colony of Black-tailed Gulls (<em>Larus crassirostris</em>) breeding on Kabushima, northeastern Honshu, Japan, in 2018 and 2019. Total Hg concentrations in blood cells in females were 2.48 ug/g dry weight ± 0.55 (1.28–3.28) in 2018 and 2.42 ug/g dry weight ± 0.55 (1.87–3.29) in 2019. In our two-year field study, female parents did not differ in Hg concentrations between two years, but δ15Ns, i.e., the difference in diet, were significantly lower in 2019 than those in 2018. The difference in δ15Ns could be related to difference in fledging success between two years (90% and 40% in 2018 and 2019, respectively). However, the results of this study showed that Hg exposure was not significantly associated with clutch size, hatching success, or nest success in the two years with different diets and was not significantly associated with any reproductive parameters at δ15N. Hg exposure was significantly negatively correlated with chick weight gain (g/day), while blood Hg accumulation in female Black-tailed Gulls was below the threshold for direct effects on breeding success. However, there was no noticeable abnormal behavior when feeding the chicks at their Hg exposure levels, under the current level value. Although the breeding numbers of Black-tailed Gulls are not thought to be declining at colonies around Japan at the moment, Hg contamination may threaten their numbers in the future.

Морские птицы острова Тайночин (залив Шелихова, Охотское море)

The north of the Sea of Okhotsk is one of the least studied areas in Russia's Far East. Tainochin Island (61°48'35"N 159°19'35"E) in the north of Shelikhov Bay, despite its small size, supports a very large seabird colony of seabirds. The first and the only survey of seabird colonies on the island was held back in 1994. In 2017 more than 1000 digital images of colonies were made during a single- day survey (7.06.2017). We used these digital photographs to count seabirds on the island in order to compare the current species composition and numbers with historical data. In 2017, the numerous species were the Common Murre and the Thick-billed Murre (more than 45.5 thousand individuals, two species combined), the Black-legged Kittiwake (more than 13.5 thousand individuals), and the Slaty-backed Gull (more than 1.5 thousand individuals). Common species included the Tufted Puffin (324 individuals) and the Pelagic Cormorant (280 individuals). Rare species embraced the Spectacled Guillemot (13 individuals) and the Horned Puffin (7 individuals). The Parakeet Auklet, observed in small numbers in 1994, was not recorded in 2017. The numbers of the Tufted Puffin may be underestimated, assumingly making about 1.5-2 thousand individuals. The total number of breeding seabirds (more than 61 thousand individuals) might have been stable for decades, despite the relative accessibility of the island to humans. The Common Murre population has slightly declined (from 47K to 44K individuals), presumably due to regular egg harvesting. Simultaneously, there has been an increase in the number of Slaty-backed Gulls and Pelagic Cormorants.

Урбанизированная популяция тихоокеанской чайки на Южных Курилах

Comparison of 2015's data on the abundance and distribution of Slaty-backed Gull nests in the settlement of Yuzhno-Kurilsk (Kunashir Island) with counts of nests and chicks conducted in 2020, permits to assess the changes that have occurred in the developing urbanized population within a shor-time period. The total number of gulls breeding on the building roofs has more than quadrupled: 80 nests in 2015 compared to 328, in 2020. All basic nesting patterns of nesting in the settlement correspond to those usual for large gulls in urbanized conditions: concentration of the nest mass in denser colonies on a few industrial and administrative buildings, nest locations near obstacles (pipes, superstructures, walls, etc.). Breeding success is high, especially in colonies (1.4 chicks per pair). Periodic struggle of people against gulls (nest destruction) leads to repeated clutches, which extends the nesting period. No other options available for safe placement of nests can cause this population nesting in the settlement.

Seasonal variation in habitat use, daily routines and interactions with humans by urban-dwelling gulls

The effects of growing urbanization have caused an increase in human-wildlife interactions in urban areas. Human-gull conflicts have been particularly studied during the breeding season when gulls cause an obvious nuisance in urban areas. However, with many gulls being present in urban areas throughout the year, stakeholders need knowledge of seasonal effects on local human-gull interaction dynamics. Here we present a comprehensive study on spatial and temporal variation of urban habitat use and human interactions with urban gulls, Larus spp., in Porto, Portugal. The work combined: (1) a large-scale study, using year-round monthly surveys to quantify gulls’ behaviour and their use of multiple urban habitats, with (2) a small-scale study, using 10-h daily urban surveys to capture gulls’ daily routines and interactions with humans during the winter and breeding seasons. We found a strong temporal effect in the number of gulls and human-gull interactions occurring in urban areas, with both highly increasing during winter. Habitats with higher urbanization intensity were mainly used by adult gulls, and the number of breeding-related conflicts reported by the human population peaked during the chick-rearing period. Still, during winter, several adult gulls kept occupying their rooftop nesting grounds, and the number of individuals foraging and interacting with humans in city-squares increased. This was mostly triggered by humans feeding birds. Therefore, when designing urban management landscape measures, seasonal variations of the urban gulls’ behaviour and habitat-use should be considered, as well as anthropogenic activities and human behaviour.

Importance of predictable anthropogenic food subsidies for an opportunistic gull inhabiting urban ecosystems

The provision of predictable anthropogenic food subsidies (PAFS) to urban wildlife has been recognized as an important trophic input in urban ecosystems. However, there is a lack of agreement about the benefits and harms of urban PAFS for avian species. While there are many studies about the impact of PAFS on birds, little information is available about the potential importance of PAFS on the ecology of urban gulls. In the present study, we aimed to evaluate the importance of human PAFS for the urban population of the yellow-legged gull (Larus michahellis) in the city of Barcelona, northeastern Spain. This opportunistic seabird is considered a pest species in urban areas. Specifically, by conducting a visual census in a location where PAFS were provided every week year-round, we examined the total number and age structure of gulls using this PAFS station. We identified the presence of yellow-legged gulls with some physical anomalies using the PAFS station. The results of this study suggest that PAFS may be an important artificial resource for urban yellow-legged gulls inhabiting Barcelona, used by either breeders or non-breeders, and also used by handicapped individuals. Based on these results, we suggest the regulation of this activity as a complement to other measures focused on the reduction of available food resources present in urban areas to manage this problematic species.

Effects of alarm call playback on the behaviour of wild European herring gulls

Playback of audio recordings is a well-established method of eliciting behavioural responses in the wild. The effects of audio playback on the behaviour of wild European herring gulls (Larus argentatus) has not been well researched however. The present study was conducted in order to address this using playback of recordings of European herring gull alarm calls, European herring gull food begging calls, a woodland dawn chorus or silence to wild free-living birds that had been attracted to the study site by the scattering of a highly palatable food mixture. Each call type was played 8–9 times in randomised order across the 40 day study period with only one call being played per day. Playback was initiated 30 s after two or more gulls had landed within the within the baited area and continued for 2 min thereafter. The number of birds on the ground within this area was recorded at 10 s intervals during the 30 s before the playing of the calls was initiated through to the 30 s afterwards. Results were clear and showed that whilst groups of herring gulls typically arrived in close temporal proximity to each other and quickly began consuming the food, they took flight within seconds of hearing their own species’ alarm calls even though there was still food left to be eaten. The woodland dawn chorus produced a similar effect for reasons that are not fully understood. The begging calls were largely without effect and as with the ‘silent’ condition numbers of gulls on the ground appeared to decrease in relation to a reducing amount of food left to be eaten. These data together demonstrate that whilst wild European herring gulls respond with flight upon hearing their own species’ alarm calls, other sounds can produce this effect also.

Urban herring gulls use human behavioural cues to locate food.

While many animals are negatively affected by urbanization, some species appear to thrive in urban environments. Herring gulls (Larus argentatus) are commonly found in urban areas and often scavenge food discarded by humans. Despite increasing interactions between humans and gulls, little is known about the cognitive underpinnings of urban gull behaviour and to what extent they use human behavioural cues when making foraging decisions. We investigated whether gulls are more attracted to anthropogenic items when they have been handled by a human. We first presented free-living gulls with two identical food objects, one of which was handled, and found that gulls preferentially pecked at the handled food object. We then tested whether gulls' attraction to human-handled objects generalizes to non-food items by presenting a new sample of gulls with two non-food objects, where, again, only one was handled. While similar numbers of gulls approached food and non-food objects in both experiments, they did not peck at handled non-food objects above chance levels. These results suggest that urban gulls generally show low levels of neophobia, but that they use human handling as a cue specifically in the context of food. These behaviours may contribute to gulls’ successful exploitation of urban environments.

Evaluating UAV-based techniques to census an urban-nesting gull population on Canada’s Pacific coast

The use of unmanned aerial vehicles, or drones, in wildlife monitoring has increased in recent years, particularly in hard-to-access habitats. We used fixed-wing and quadcopter drones to census an urban-nesting population of Glaucous-winged Gulls in Victoria, Canada. We conducted our study over 2 years and asked whether (i) drones represent a suitable survey method for rooftop-nesting gulls in our study region; and (ii) Victoria’s urban gull population had increased since the last survey &gt;30 years earlier. Using orthomosaic imagery derived from drone overflights, we estimated at least a threefold increase over the 1986 count reported for the entire city (from 114 to 346 pairs), and an approximate tenfold increase in the number of gulls nesting in the downtown core. Drones proved to be an excellent platform from which to census rooftop-nesting birds: occupied nests were readily discernible in our digital imagery, and incubating birds were undisturbed by drones. This lack of disturbance may be due to Victoria’s location in an aerodrome; gulls experience dozens of floatplane and helicopter flights per day and are likely habituated to air traffic. Glaucous-winged Gulls have declined considerably at their natural island colonies in the region since the 1980s. Our results indicate that although urban roofs provide replacement nesting habitat for this species, local gull populations have not simply relocated en masse from islands to rooftops in the region.

Effects of Age and Culling on Movements and Dispersal Rates of Yellow-Legged Gulls (Larus michahellis) from a Western Mediterranean Colony

This study reports the effects of age and culling of breeding adults on movements and dispersal rates of Yellow-legged Gulls (Larus michahellis) from a western Mediterranean colony (the Medes Islands) based on recaptures and resightings of birds banded as chicks. Juveniles (1-year-old birds) were most frequently located in the French coast of Biscay and in the Western North Mediterranean. Older gulls became concentrated near the colony and its surroundings (core area), with 3rd year sub-adults and adults accounting for more than 70% and 90% of resightings in this area, respectively. Culling of breeding adults increased the dispersal rate of juveniles (pre-cull: 62.6% ± 6.0 SD; post-cull: 71.2% ± 6.4 SD) and mean distance of resightings of juveniles (pre-cull: 250.5 km ± 267.6 SD; post-cull: 367.6 km ± 300.1 SD), and favored displacement of juveniles to the French Atlantic coast. Culling also increased the dispersal rate of adults (pre-cull: 31.7% ± 16.6 SD; post-cull: 38.8% ± 16.3 SD) and mean distance of adult resightings (pre-cull: 27.4 km ± 108.7 SD; post-cull: 35.7 km ± 113.0 SD). This could be attributed to an increase in the number of gulls recruited to other colonies near the Medes Islands after culls. Culling performed in the Medes Islands colony seems to have effects at metapopulation level, conditioning the dynamics and management of other colonies.

Predator-prey dynamics of bald eagles and glaucous-winged gulls at Protection Island, Washington, USA.

Bald eagle (Haliaeetus leucocephalus) populations in North America rebounded in the latter part of the twentieth century, the result of tightened protection and outlawing of pesticides such as DDT. An unintended consequence of recovery may be a negative impact on seabirds. During the 1980s, few bald eagles disturbed a large glaucous‐winged gull (Larus glaucescens) colony on Protection Island, Washington, USA, in the Salish Sea. Breeding gull numbers in this colony rose nearly 50% during the 1980s and early 1990s. Beginning in the 1990s, a dramatic increase in bald eagle activity ensued within the colony, after which began a significant decline in gull numbers.To examine whether trends in the gull colony could be explained by eagle activity, we fit a Lotka–Volterra‐type predator–prey model to gull nest count data and Washington State eagle territory data collected in most years between 1980 and 2016. Both species were assumed to grow logistically in the absence of the other.The model fits the data with generalized R 2 = 0.82, supporting the hypothesis that gull dynamics were due largely to eagle population dynamics.Point estimates of the model parameters indicated approach to stable coexistence. Within the 95% confidence intervals for the parameters, however, 11.0% of bootstrapped parameter vectors predicted gull colony extinction.Our results suggest that the effects of bald eagle activity on the dynamics of a large gull colony were explained by a predator–prey relationship that included the possibility of coexistence but also the possibility of gull colony extinction. This study serves as a cautionary exploration of the future, not only for gulls on Protection Island, but for other seabirds in the Salish Sea. Managers should monitor numbers of nests in seabird colonies as well as eagle activity within colonies to document trends that may lead to colony extinction.

Exclusion of Ring-billed Gulls (Larus delawarensis) from recreational beaches using canid harassment

Abstract Ring-billed Gull (Larus delawarensis) populations have dramatically increased throughout their geographic range with the largest concentrations in the Great Lakes region of Canada and the United States. Large populations of gulls cause conflict with humans at recreational beaches, where their effects on human health and safety include bacteria contamination from gull feces. We used border collies to harass and exclude gulls from beaches in summer 2012 and 2013, then measured gull numbers and Escherichia coli. Dogs were effective at reducing gull numbers by 56–76% during continuous and noncontinuous dog treatment periods. Levels of E. coli were lower on dog-treated beaches, but only during the first half of the summer. Mixed modeling analysis showed presence of dogs was a strong predictor of gull numbers and E. coli levels, with variation among dogs, possibly related to age. Noncontinuous use of dogs, applied within an integrated beach management framework, can provide a nonlethal method for reducing gull use and E. coli levels at recreational beaches.