Gull Attacks Research Articles

Acute and chronic behavioral effects of kelp gull micropredation on southern right whale mother-calf pairs off Península Valdés, Argentina

Kelp gullsLarus dominicanus(KG) feed on the skin and blubber of living southern right whalesEubalaena australis(SRWs) off Península Valdés (PV), Argentina. The whales respond strongly to KG micropredation by changing their immediate (acute) behavior during attacks and their overall (chronic) surfacing pattern and body posture to minimize gull exposure. The energetic and large-scale behavioral consequences of these attacks are unknown. To address this knowledge gap, we quantified the effect size of both acute (during attacks) and chronic (not during attacks) responses by comparing the respiration rates, swim speed, and nursing behavior of PV SRWs to undisturbed (control) SRW mother-calf pairs in Head of Bight, Australia, using unmanned aerial vehicle focal follows. Even when gulls were not attacking, PV SRW mothers and calves demonstrated ~50 and ~25% higher respiration rates, respectively, than whales in Australia. During attacks, PV calf respiration rates increased by an additional 10%. PV SRW mothers also frequently (>76% of respirations) exhibited irregular breathing postures, causing the whales to potentially expend extra energy by working against their natural buoyancy. Despite no significant increase in average maternal swim speed, 76 and 90% of gull attacks elicited strong behavioral reactions from mothers and calves, respectively. Overall, PV calves spent less time nursing during individual bouts compared to those in Australia but entered suckling position more frequently. Furthermore, kelp gulls seemed to show a preference for attacking previously wounded calves and at a higher rate. These chronic and acute behavioral effects may carry energetic costs, which could have long-term consequences for SRW survival and reproduction.

Gull attacks on migrating birds at Ada Island (S Montenegro)

Abstract Migration poses a high risk to birds. Crossing of large bodies of water is especially demanding for land birds. One of the dangers faced by migrants are opportunistic predators like gulls. Most gulls Laridae are generalist predators with omnivorous diets. Attacking on migrating birds was investigated during ground observations of bird migration at Ada Island (S Montenegro) between 17 Mar and 10 Apr 2015. We recorded 20 attacks on 22 individuals of six species and on one unidentified passerine. In four instances gulls attacked birds of prey, in two Hoopoe Upupa epops and in 16 passerines. Except for two cases when small flocks of two birds were attacked, gulls attacked individuals migrating singly. Considering our data around one percent of passerines migrating during the day across the southern Adriatic Sea can expect to be attacked by gulls. This percentage can be as high as 9.5% for passerines migrating singly.

Lifetime glucocorticoid profiles in baleen of right whale calves: potential relationships to chronic stress of repeated wounding by Kelp Gulls.

Baleen tissue accumulates stress hormones (glucocorticoids, GC) as it grows, along with other adrenal, gonadal and thyroid hormones. The hormones are deposited in a linear fashion such that a single plate of baleen allows retrospective assessment and evaluation of long-term trends in the whales' physiological condition. In whale calves, a single piece of baleen contains hormones deposited across the lifespan of the animal, with the tip of the baleen representing prenatally grown baleen. This suggests that baleen recovered from stranded carcasses of whale calves could be used to examine lifetime patterns of stress physiology. Here we report lifetime profiles of cortisol and corticosterone in baleen of a North Atlantic right whale ('NARW'-Eubalaena glacialis) calf that died from a vessel strike, as well as four southern right whale ('SRW'-Eubalaena australis) calves that were found dead with varying severity of chronic wounding from Kelp Gull (Larus dominicanus) attacks. In all five calves, prenatally grown baleen exhibited a distinctive profile of elevated glucocorticoids that declined shortly before birth, similar to GC profiles reported from baleen of pregnant females. After birth, GC profiles in calf baleen corresponded with the degree of wounding. The NARW calf and two SRW calves with no or few gull wounds had relatively low and constant GC content throughout life, while two SRW calves with high numbers of gull wounds had pronounced elevations in baleen GC content in postnatal baleen followed by a precipitous decline shortly before death, a profile suggestive of prolonged chronic stress. Baleen samples may present a promising and valuable tool for defining the baseline physiology of whale calves and may prove useful for addressing conservation-relevant questions such as distinguishing acute from chronic stress and, potentially, determining cause of death.

Erysipelothrix rhusiopathiae isolated from gull-inflicted wounds in southern right whale calves.

Southern right whales Eubalaena australis from Peninsula Valdés, Argentina, show wounds produced by kelp gulls Larus dominicanus that feed on the whales' dorsal skin and blubber. During the 2013 whale season, several calves were reported showing kelp gull injuries with a swollen area surrounded by rhomboid-shaped raised edges. Samples from 9 calves were taken in order to establish the etiology of these rhomboid-shaped wounds; 2 calves (one living, one dead) showed gull-inflicted injuries with rhomboid-shaped edges. Samples from the dead calf were histologically characterized by the presence of dermal congestion, suppurative dermatitis and panniculitis, necrotizing vasculitis and vascular thrombosis. Erysipelothrix rhusiopathiae was detected by culture and PCR in samples from both calves. In this study we report, for the first time to our knowledge, the isolation of E. rhusiopathiae from wounds produced by gull attacks on southern right whale calves, supplying evidence that these wounds may act as an entry route for pathogens. This work provides new information about the consequences of gull-inflicted injuries for whale health.

Increased Wounding of Southern Right Whale (Eubalaena australis) Calves by Kelp Gulls (Larus dominicanus) at Península Valdés, Argentina.

At least 626 southern right whale (Eubalaena australis) calves died at the Península Valdés calving ground, Argentina, between 2003 and 2014. Intense gull harassment may have contributed to these deaths. In the 1970s, Kelp Gulls (Larus dominicanus) began feeding on skin and blubber pecked from the backs of living right whales at Valdés. The frequency of gull attacks has increased dramatically over the last three decades and mother-calf pairs are the primary targets. Pairs attacked by gulls spend less time nursing, resting and playing than pairs not under attack. In successive attacks, gulls open new lesions on the whales’ backs or enlarge preexisting ones. Increased wounding could potentially lead to dehydration, impaired thermoregulation, and energy loss to wound healing. The presence, number and total area of gull-inflicted lesions were assessed using aerial survey photographs of living mother-calf pairs in 1974–2011 (n = 2680) and stranding photographs of dead calves (n = 192) in 2003–2011. The percentage of living mothers and calves with gull lesions increased from an average of 2% in the 1970s to 99% in the 2000s. In the 1980s and 1990s, mothers and calves had roughly equal numbers of lesions (one to five), but by the 2000s, calves had more lesions (nine or more) covering a greater area of their backs compared to their mothers. Living mother-calf pairs and dead calves in Golfo Nuevo had more lesions than those in Golfo San José in the 2000s. The number and area of lesions increased with calf age during the calving season. Intensified Kelp Gull harassment at Península Valdés could be compromising calf health and thereby contributing to the high average rate of calf mortality observed in recent years, but it cannot explain the large year-to-year variance in calf deaths since 2000.

Change in southern right whale breathing behavior in response to gull attacks

Animals may develop behavioral responses to avoid discomforting situations. In particular, pain can result in learned avoidance behaviors. We report such a case in southern right whales (Eubalaena australis) that have been the target of attacks by kelp gulls (Larus dominicanus) that feed on their skin and blubber in the surrounded waters of Peninsula Valdes, Chubut (Argentina) since the 1980s. The increase in the attacks over the years triggered on whales the development of alternative postures to keep their backs protected from the gulls. Recently, a particular avoidance behavior has been observed, the “oblique breathing,” in which whales breathe with only the head out of the water. The main goal of this work is to describe the emergence of oblique breathing in two areas of Golfo Nuevo (P. Valdes) which have high number of whales and gull attacks, during the whale reproductive seasons in 2010, 2012 and 2013. Results suggest that all age and sex classes of whales can breathe obliquely. Emergence of the oblique breathing seems to have proceeded in three stages: (1) the origin, with rare observations, (2) the spread, when the behavior was registered only during gull attacks and (3) the establishment, when whales performed it in a preventive manner, even when attacks were not occurring. Oblique breathing is likely to pose extra energy costs, which could be detrimental to whales, especially for recently born calves. However, given the increasing prevalence of this behavior, it seems to be a useful strategy to prevent harassment by gulls.

Kelp gulls attack Southern right whales: a conservation concern?

Kelp gulls (Larus dominicanus) feed on pieces of skin and blubber they rip from Southern right whales’ (Eubalaena australis) backs in their breeding areas at Peninsula Valdes, Argentina, producing injuries. This behavior has increased since the first record in 1972, and some authors have suggested that constant gull harassment could have a negative effect on right whale population. The main goal of this study is to assess the variables that most affect the gull attacks. We analyzed 5359 whale-watching sightings made during trips from Puerto Piramides (42o34′S, 64o16′W) along the whale breeding seasons (June–December) 2005 to 2007. The most important factors affecting the attacks include the presence of a mother–calf pair, the time within the season, the distance to the coast and the wind velocity. There is also concern of possible transmission of infectious diseases in the attacks since increasing number of whales with different patterns of skin lesions have been observed.

Choosing among mobile prey species: Why do gulls prefer a rare subtidal crab over a highly abundant intertidal one?

In New England, Herring Gulls (Larus argentatus) and Great Black-backed Gulls (L. marinus) are generalist predators that forage on highly mobile prey in intertidal and shallow subtidal zones, including three species of crabs: Cancer borealis, C. irroratus, and Carcinus maenas. Carcinus is more abundant than are C. irroratus and C. borealis and yet both Cancer species are more common in the diet of gulls. In this study we used a series of experiments to examine why gulls exhibit disproportionately higher predation on C. borealis relative to the two other crab species. We found that gulls do not discriminate among crab species when presented crab tissue “patties” indicating that gulls do not select crabs based on differences in palatability. At smaller size ranges (<75mm carapace width), C. irroratus had lower dry tissue weight than the other two species, thus gulls should prefer similar-sized C. borealis and Carcinus based on their caloric value. At carapace widths greater than 80mm, C. irroratus had higher available dry tissue weight than C. borealis. However, C. borealis is generally larger than C. irroratus in the intertidal and shallow subtidal zones so this difference is unlikely to contribute to a preference for C. irroratus. Our experiments showed that algal species dominating rocky ledges provide a cryptic refuge for Carcinus thereby reducing the likelihood of attack by gulls. We found that the “lateral merus” display exhibited by C. irroratus appears to deter attacks by gulls; in contrast, C. borealis withdraw their chelae in response to attack, which likely facilitates their capture by gulls. During simulated gull attacks, Carcinus exhibited escape behavior whereas C. borealis remained stationary. Lack of escape behavior likely facilitates capture of C. borealis by gulls. In sum, our findings suggest that gulls have formed a search image for C. borealis, which is likely a result of the relative ease of capture and profitability of C. borealis compared to Carcinus and C. irroratus. Gull preference for C. borealis has important consequences for crab distributions and the structure of rocky intertidal and shallow subtidal zones in New England. In particular, gulls create a refuge for Carcinus in the intertidal zone by reducing densities of C. borealis, a potential predator and competitor, and by avoiding preying upon Carcinus.

Gull Predation and Breeding Success of Common Eiders on Stratton Island, Maine

Common Eider (Somateria mollissima dresseri) breeding success and gull-eider interactions were studied at Stratton Island, Maine in 2004 and 2005. Eiders suffered little nest predation, and most egg losses to gulls were either facilitated by researcher intrusions or confined to newly initiated, unattended nests. Despite high nest success (>80%) in both study years, predation watches indicated that few, if any, ducklings survived to fledging as a result of extreme harassment and predation by Great Black-backed Gulls (Larus marinus). Gull attacks were opportunistic, involved one to 36 gulls, and often resulted in complete crèche destruction. Herring Gulls (L. argentatus) also took occasional young and eggs. Although Stratton Island is managed as a tern restoration site, and gull control measures to enhance tern productivity include nest destruction and shooting of tern predators, gulls continued to congregate around crèching areas and to prey on ducklings. We suggest that additional gull control measures, particularly at a nearby gull colony, may enhance duckling survival. We also recommend monitoring of other eider colonies in the region to better assess duckling survival and recruitment rates.

The effects of disturbance caused by boating on survival and behaviour of velvet scoter Melanitta fusca ducklings

We studied the consequences of human disturbance and gull predation on brood survival of velvet scoter Melanitta fusca in the Archipelago of South-West Finland in 1990 and 1991. Each brood was exposed to disturbance by boats on average 8·5 times a day in 1990 and 3·5 times a day in 1991. Disturbance lengthened the swimming distances of ducklings and reduced the time used for feeding. Broods disturbed more frequently than average were smaller than those disturbed less frequently. At least 60% of ducklings died before the age of three weeks. The common predators of ducklings in the study area are the herring gull Larus argentatus and the great black-backed gull Larus marinus. The daily predation rate by gulls on velvet scoter ducklings was 4·7%, which means that 56% of ducklings are caught by gulls during the first three weeks. The frequency of gull attacks was 3·5 times higher in disturbed than in undisturbed situations.

The Role of Failed Nesters and Brood Abandoning Females in the Creching System of the Common Eider Somateria mollissima

In Common Eiders, females other than the mother often protect young from predators. This study was designed to determine if failed nesters and females which loose their young shortly after hatching (brood abandoners) participate in such rearing activities. Brood caring females always reacted aggressively towards approaching gulls and stayed close to the young during disturbance. The behaviour of failed nesters and brood abandoners towards broods and creches was similar. Their creche attendance was highly temporal and independent of the time since they had lost their eggs or hatched their young. They usually left the creches at the slightest disturbance, and during gull attacks failed nesters showed no reaction while a few brood abandoners tending creches reacted aggressively. Most of the creche attendance in nest-failing and brood abandoning females is presumably motivated by selfish interest, e.g. seeking safety from predators or kleptoparasites. The so-called visiting females or aunts in Eider creches should be divided in two categories: broody females showing protective behaviour and females temporarily attending creches and showing no broodiness. Failed nesters and most of the brood abandoners belong to the latter category. Most of the females showing protective behaviour probably belong to the non-breeding cohort (young and/or non-breeding birds).

Herring Gull Attacks Eared Grebe

Herring Gull Attacks Eared Grebe