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With an increasing human population and expansion of urban settlements, wild animals are often exposed to humans. As humans may be a threat, a neutral presence or a source of food, animals will benefit from continuously assessing the potential risk they pose in order to respond appropriately. Herring gulls, Larus argentatus, are increasingly breeding and foraging in urban areas, and thus have many opportunities to interact with humans. We recently found that herring gulls take longer to approach food when being watched by a human. However, it is not known whether aversion to human gaze arises from experience with humans, and whether individual differences in responsiveness are a result of differential exposure. Here, we tested whether herring gulls' responses to human gaze differ according to their age class and urbanization of their habitat. We measured the gulls' flight initiation distance when an experimenter approached with either a direct or an averted gaze. Neither gull age class nor urbanization significantly influenced the effect of human gaze on flight initiation distance. However, as recently fledged juveniles responded strongly to the experimenter's gaze, aversion to human gaze may not require extensive exposure to humans to develop. Gulls in urban areas could be approached more closely than those in rural areas, consistent with findings in other species. These results indicate that gaze aversion is present early in development and that exposure to humans may influence gulls' responses to perceived risk from humans. Investigating the processes generating individual differences in responses to humans will provide further insights into human–wildlife interactions and the effects of urbanization.

Kleptoparasitism is a foraging strategy where one individual steals a procured food item from another individual. Individual kleptoparasites can optimize their foraging strategy by targeting more profitable hosts or by modifying their behaviour to expend less energy than they would by foraging independently. Herring gulls, Larus argentatus, kleptoparasitize Atlantic puffins, Fratercula arctica, by intercepting adults as they return to their burrows with fish for their chicks. While this system has been studied extensively, much remains unknown, particularly from the herring gull's perspective. We tested predictors of herring gull host choice and the probability of success during kleptoparasitic attacks by conducting 73 30-minute focal samples of individual herring gulls at a breeding colony in Newfoundland, Canada. We recorded each puffin that approached the focal gull, categorizing them according to prey type carried, whether or not they landed, and whether or not they were attacked. For those puffins that were attacked, we also noted whether the gull succeeded in obtaining prey. Herring gulls did not attack puffins at random, but, rather, preferentially attacked puffins that carried larger prey, had already completed their landing, and landed closer to and/or in front of the gull. Gulls tended to be more successful at stealing a puffin's food when they attacked landed puffins and made physical contact with the puffin, but not when the puffin landed closer to them or when they were oriented towards the puffin. These findings suggest that herring gulls optimize their kleptoparasitic foraging strategy by targeting more profitable hosts.

Recent studies have demonstrated the presence of risk-based variation in alarm calling in many vertebrate species. Most of the studies on birds, however, have focused on passerine systems perhaps due to the traditional view that passerine vocalizations are more complex. We investigated the presence of a risk-based alarm calling system in a nonpasserine, the herring gull, Larus argentatus, by recording birds presented with varying degrees of threat, and experimentally exposing and quantifying responses to manipulated alarm calls. We found that herring gulls communicate threat urgency in their alarm calls using both frequency and time parameters. Sound recordings indicated that herring gulls change centre frequency modulation patterns of their alarm calls, generate frequency discontinuities in notes and increase the rate of calling with increases in perceived threat level. Playback experiments showed that conspecifics pay attention to both frequency and time parameters and respond most urgently to playbacks of high-threat calls at a high call rate. A less urgent response to high-threat calls at a low call rate and to low-threat calls at a high call rate suggests that threat urgency information is reinforced by both call type and call rate in the herring gull system. This study is one of the first demonstrations of a risk-based alarm calling system in a nonpasserine.

Young herring gull, Larus argentatus, chicks peck at the red patch on the lower mandible of their parent's yellow beak. In a famous study on the ‘instinctive behaviour’ of herring gull chicks, Tinbergen examined whether the presence, colour and position of the patch affected the pecking of the chicks. While this experiment is often cited as demonstrating a preference for a red patch, the original data showed that chicks pecked more at a black-patched model (Tinbergen 1948, De Levende Natuur, 51, 49–56). Tinbergen later ascribed this unexpected outcome to a methodological error in his experiment: the red-patched model was presented more frequently than all the others, which made him adjust his data later on. We repeated Tinbergen's experiment (experiment 1), using replicas of the original models. We also did the experiment as Tinbergen described it later on (but which he never carried out), presenting all models equally often (experiment 2). Our results confirm that red is not the most preferred colour when it is presented more often than other colours. In experiment 2 the relative ranking of all models was the same as in experiment 1, with the exception of the red-patched one, which was now preferred most, as expected by Tinbergen. Our findings also confirm that the more frequent exposure to the red model in experiment 1 resulted in a disproportionate decline in interest for this model. So, although he never did the actual experiment, Tinbergen's intuition and corrected data show a reasonable match to the results of our experiment.

One of the classic studies in animal behaviour is that by Niko Tinbergen on the stimuli that elicit begging behaviour in young herring gull, Larus argentatus, chicks. Tinbergen examined which features of the beak induced chicks to peck by using various cardboard models of herring gull heads in different shapes and colours. Leiden University, home university to Tinbergen at the time, still has a summarizing overview of the data of the initial experiment of the study. In that experiment, models with a yellow beak with patches in various colours and different positions were presented to young chicks. In this essay, I relate those earliest data to the various publications in which Tinbergen discussed them over the years. Subsequent publications became more and more detached from the original data, resulting in sizeable discrepancies between the original study and later descriptions of when and how the experiment was done and its outcome. I first sketch the scientific context of the herring gull study. Next I present the original data and document the subsequent changes. I discuss what might have led Tinbergen to modify his account of the study over the years, relating it both to its historical context and to the issue of ‘expectancy biases’.

Behavioural field observations are increasingly being used in ecotoxicological research to identify potential adverse effects of exposure to persistent organic pollutants (POPs). We investigated thermal conditions inside the nest and parental behaviour of glaucous gulls, Larus hyperboreus , breeding in the Norwegian Arctic in relation to the concentrations of major classes of POPs (organochlorines, brominated flame retardants and metabolically derived products) accumulated in their blood. Most notably, nest temperature was negatively correlated with the concentrations of the sum of (Σ) DDT, ΣPCB and several quantitatively minor POP classes within the incubating parent. To investigate the relationship between incubation ability and parental POP exposure further, we experimentally increased the costs of incubation by artificially increasing the clutch size from two to four eggs. Clutch enlargement was followed by a decrease in nest temperature, but this drop in temperature was not associated with POP concentrations within the incubating parent. However, males, which had higher POP concentrations and lower white blood cell counts than females, seemed less able to maintain nest temperature. There was virtually no evidence to suggest that ΣPCB or ΣDDT were associated with changes in the time a bird spent incubating. However, there was some indication that nest site attendance by nonincubating males was negatively related to ΣDDT, suggesting that nest protection may have been compromised. The results suggest that adverse effects of parental POP exposure may occur through suboptimal thermal conditions for embryo development and possibly increased egg predation risk.

Physical attributes of a nest site can be important in determining the outcome of a breeding event. However, high-quality individuals may be more able to obtain particular sites, and thus habitat quality and individual quality are often confounded in correlative studies. We examined the potential sheltering effect of nest vegetation on the nest microclimate and on the behaviour and breeding performance of herring gulls, Larus argentatus. In addition to comparing birds at unmanipulated vegetated and unvegetated sites, we experimentally manipulated vegetation around nests to tease apart breeder quality and habitat effects. Birds nesting at unmanipulated vegetated sites had earlier laying dates, heavier eggs and more fledglings than those at comparable unvegetated sites. Vegetation provided shelter from weather conditions for the incubating birds and chicks; vegetated nest sites had on average milder air temperatures and lower wind speeds than unvegetated control nest sites. During incubation, breeders at naturally vegetated nests assumed alert postures less, and spent more time sleeping, than those at naturally unvegetated sites, indicating less disturbance from neighbours. In nests where vegetation was experimentally removed, both nest microclimate and breeder behaviour became similar to those at the naturally unvegetated nests; however, despite these changes, the absence of vegetation did not alter the higher breeding performance of birds at these sites. Therefore, nest microclimate alone is not responsible for the improved performance at vegetated sites; such sites appear to be occupied by better-quality individuals.

Behaviours with no apparent adaptive function are sometimes described as play without rigorous testing of alternative explanations. One such behaviour is the repeated dropping and catching of objects by birds. We observed drop-catch behaviour by herring gulls over 3 years at a site where the birds frequently dropped clams to break them on hard surfaces below. We tested unique suites of predictions from three hypotheses, that the drop-catch behaviour is play, that it functions to expose potential kleptoparasites, or that it serves to reposition clams before foraging drops. We tested data from 72 drop-catch series and 504 typical foraging drop series to determine which suite of predictions most closely matched our observations. As predicted if the behaviour were play, drop-catches were performed more by younger birds, not necessarily over a hard substrate, and sometimes with nonfood objects. Clams that were subjected to drop-catches were generally not repositioned or eaten. These results suggest a motivation for drop-catching that is distinct from foraging. Finally, drop-catches were more frequent when it was warm and when there were high winds, also consistent with the play hypothesis. Drop-catch behaviour closely matched the predictions of the play hypothesis and we were able to reject the two alternative explanations.

Microphallus piriformes (Trematoda) is unusual in having only two hosts and no motile free-living stages. The intermediate host, the rough periwinkle, Littorina saxatilis, is present year-round on rocky shores and has a high parasite prevalence near breeding colonies of the definitive host, the herring gull, Larus argentatus, which is present in numbers at these sites for only 4 months per year. Given the seasonal availability of gulls for infection and a low incidence of periwinkles in the normal diet of herring gulls, specialized transmission between stages appears necessary for maintenance of the parasite's life cycle. We investigated the hypothesis that M. piriformes alters its intermediate host's behaviour during the gull's breeding season in a manner that may facilitate predation of the infected periwinkle by breeding gulls. We studied the movements of periwinkles during simulated tidal cycles in the laboratory; parasite status was established subsequently. Periwinkles with mature infections moved further upwards but showed less downwards and horizontal movement than uninfected periwinkles. The movement of periwinkles with immature (nontransmissible) infections was less affected by the parasite. During the tidal cycle, infected and uninfected periwinkles differed in both timing and extent of movement. A field experiment confirmed the greater upwards movement of infected periwinkles. The parasite-induced changes in periwinkle behaviour may increase the chances of predation by the final host and could represent an important survival strategy for M. piriformes. Copyright 2000 The Association for the Study of Animal Behaviour.

In common gull colonies on islands of the Vistula River, Poland, adoption of chicks is common. In 1997, we observed 81 chicks from 35 nests. Of these, 19 (23.4%) left their natal broods and were adopted by other pairs. Another 11 (31.4%) were driven from the foreign territory by the owners. Foreign chicks were adopted by 15 pairs (42.9%). Eleven pairs (31.4%) drove foreign chicks from the territory. To test if the frequent adoptions in these colonies could be explained by kin selection or the occurrence of kin groups, we calculated band-sharing coefficients and genetic relatedness (r) between interacting birds (neighbours and non-neighbours). Adults that adopted were most often neighbours of the biological parents of adopted chicks, whereas spatially segregated birds, nesting further away, usually drove off the chicks. Band-sharing coefficients between males, but not females, were higher with decreasing internest distances. The band-sharing coefficients for adopted chicks and foster parents were significantly higher than for adopted chicks and randomly selected, spatially segregated pairs from the same and another colony. Band-sharing coefficients of adopted chicks and adopting neighbours (males: r=0.20; females: r=0.16) also tended to be higher than those of rejected chicks and rejecting neighbours (both sexes: r=0.08). Our results suggest that kin groups of neighbours do occur in common gull colonies. Such social structure might lead to indirect inclusive fitness benefits of adopting pairs. Differences in genetic similarity between chicks and adopting or rejecting neighbours show that at least in common gulls we should consider kin altruism as a factor in adoptions. Copyright 2000 The Association for the Study of Animal Behaviour.

Savannah sparrows, Passerculus sandwichensis breeding on Kent Island, New Brunswick, Canada, have two types of nest predators, one of them (herring gulls, Larus argentatus ) abundant but relatively ineffective, the other (American crows, Corvus brachyrhynchos ) scarce but highly effective. We hypothesized that the net effect for Savannah sparrows of nesting near gulls would be to reduce the overall risk of nest predation. Despite being surrounded by predators, the eggs and offspring of sparrows that nested among gulls survived as well during the incubation and post-fledging periods as did those of sparrows that did not nest among gulls. During the nestling period, sparrows nesting among gulls had significantly lower predation rates. In defending their own nests from predatory crows, gulls apparently shielded nearby sparrows from the more dangerous predator. Experiments with model predators demonstrated that sparrows reacted to gulls as potential predators of their eggs and nestlings. Sparrows apparently recognized crows as a far greater threat, however. The tendency to nest near gulls appeared not to be heritable or influenced by early experience. Sparrows nesting among gulls were indistinguishable from sparrows nesting away from gulls in terms of body size, age and date of nesting. By choosing nest sites in microhabitats that gulls avoided, such as dense patches of goldenrod and blueberry, and by adopting more cautious approaches to their nests, sparrows nesting near gulls reduced their risk of predation by gulls. The density of Savannah sparrow nests was inversely correlated with the density of gull nests, which suggests that sparrows avoided gulls despite the apparent advantage in terms of reduced nest predation by crows. A strong nesting association between gulls and birds like Savannah sparrows is unlikely to evolve because of the low heritability of the trait, gene flow from other populations where avoiding gulls and other potential predators is selectively advantageous, and constraints on short-lived birds in learning to differentiate situations in which a predator presents a threat from those in which it provides protection.

Measures of adult feeding and foraging behaviour in the California gull, Larus californicus , were related to the growth of their offspring. Offspring showed significantly higher growth when average feeding interval, a measure of the time interval between feedings, and feeding latency following foraging decreased. The amount of time parents foraged was positively related to offspring growth and negatively correlated with average feeding interval. Either (1) increased foraging efficiency with parental age, or (2) increased reproductive effort with age, could explain age-related differences in patterns of feeding behaviour and their impact on offspring growth. However, data on foraging time support only the hypothesis of increased reproductive effort with parental age.

The regular provision of a sufficient quantity of food on the territory of pairs of breeding herring gulls led to an increase in the time individuals spent on the territory during the day, relative to controls. This ‘extra’ time was not used to increase overall sleeping time, as predicted. Instead, the experimental gulls reduced their overall sleep time due to a decline in front-sleep. Back-sleep remained relatively unaffected, with both groups spending similar amounts of time in this posture. The consequences of the two postural types of sleep were examined with respect to the cost of allowing intruders to remain on an owner's territory. Intruders arrived more often on control territories and stayed longer when only one pair member was present. Intruders were seen on control territories for more consecutive scans when the solitary control gull was in a sleep posture, particularly front-sleep. It is concluded that these results imply a difference in the consequences resulting from the two sleep postures and give additional support for the multiple function hypothesis of sleep.

It is often suggested that colonial breeding reduces nest predation for birds with a high defence capacity, but experimental comparison of predation at solitary and colonial nests is seldom feasible within a single species. We here report on such a test in the common gull (Larus canus). The rate of predation on experimental eggs was significantly lower near colonies than near solitary gull nests, and the eggs survived longer at the edge of a colony than farther away. Communal mobbing of nest predators is the likely reason. In both of two years, almost all nests of solitary gulls were destroyed by predators, while most clutches survived in colonies. Nest predation hence selects strongly for colonial breeding in the present population of common gulls.

Aspects of the feeding success and behaviour of herring gulls Larus argentatus at refuse tips were investigated during the winter of 1981–1982. Feeding occurs in mixed flocks of adult and immature gulls and is highly competitive. Comparisons were made between five age-classes of gulls (adults and immature birds in their first, second, third and fourth years). Immature herring gulls were less successful than adults both in finding and extracting edible items from the refuse. The feeding strategy of immature birds involved more energy expenditure per unit of food gained than that of adults, and was therefore less efficient. Foraging ability improved over the first 4 years of life, 4-year-olds being almost as successful as adults. Over this period foraging skills are learnt and perfected, and competitive ability improves. It is suggested that this relates to the delay in the time of first breeding.

Reports of adoptions by parent herring gulls have raised doubts about the existence and adaptiveness of a parent-young recognition system in this species. In experiments with 6–8-day-old young, we show that young do recognize their parents' vocalizations. We suggest that the particular parent-young recognition system in this species has evolved as a behavioural strategy that functions to reduce the risk of making high-cost recognition errors that could result in a parent attacking its own offspring.

This investigation was designed to examine the development of nesting habitat recognition and preferences as a function of habitat and social stimuli in neonatal Herring Gull chicks. The initial experiment studied the daily development of nest site preference during the first week post-hatch and thereafter weekly development until fledging the test procedure, which was essentially the same for all experiments, consisted of relocating chicks 20m from the nest and observing their movements. During these observations, latency, time moving, initial orientation, final distance from the nest, and initial and final vegetation characteristics were recorded. Results indicate that Herring Gull chicks exhibit a preference for the nest site area during the first week post-hatch and this preference wanes after the first week until fledging. Chicks of all ages showed a preference for vegetation similar to that of the nest site area. Nest site preferences are ecotypically controlled since foster-reared chicks exhibited the same preference for their foster nest as did normal-reared chicks for their natural nests. -- Several experiments examined the effect of vegetation characteristics and social stimuli provided by other chicks on nest site attachment and recognition. Vegetation type and the presence of siblings were found to be important stimulus properties of the nest situation in nest area attachment. Chicks exhibited a preference for vegetation similar to that at the nest site and for siblings over non-siblings. Nest site recognition appeared to be predominantly a visual response, at least in visually experienced animals. Vegetation characteristics, landmarks and the presence of other chicks were found to be among the cues used to recognize the nest site. The results of these experiments were interpreted as supporting the hypotheses that nesting habitat preferences are evident in Herring Gulls during the prefledging period and that habitat and social stimuli are important in the development of nest site preferences and recognition. These neonatal habitat preferences may be influential in determining later preferences for nesting sites and may be responsible for the observed stereotypy in adult habitat preferences.

A measure of fitness applicable to herring gull (Larus argentatus) life histories is introduced and related to short-term risks which depend on behaviour. This allows calculations of the relationship between fitness and behaviour if one can measure the risks an animal takes behaving in particular ways in specified situations. This method is used to evaluate the fitness of herring gulls during the incubation period at Walney Island, U.K. Two causes of egg mortality are considered, death by predation and death by exposure, and the latter is shown to be less important than the former. The chances of death by predation depend on the number of adults present on the territory and are estimated to be approximately 0·045 eggs per h if no parents are present on territory, 3·5×10−4 eggs per h if one parent is present and 6·7×10−4 eggs per h if two parents are present. Adult death by starvation is assumed to occur when energy reserves are exhausted; however a fitness cost is incurred if an animal maintains excess energy reserves. To restrict the number of behaviour sequences examined to manageable proportions, attention is restricted to the behaviour sequences that result from decision rules in which feeding occurs when energy reserves fall below a set point. Then optimal behaviour is characterized by (1) energy reserves maintained between 500 and 1200 kcal; (2) complementarity of mates' feeding preferences such that at least one of the pair feeds at a refuse tip; (3) parental desertion of offspring if energy reserves fall below 200 kcal; (4) parents spending the minimum possible time together on territory. These results are shown by sensitivity analysis to be insensitive to parameter errors in the model. Treating these characteristics of optimal behaviour as predictions about actual behaviour reveals that predictions 1 and 2 are correct, and prediction 4 is wrong. An experiment was designed to test prediction 3 by estimating the fat reserves of life birds and measuring how long each would continue incubation in the absence of its mate. Fatter birds did continue incubation for longer though the quantitative detail did not match prediction 3 exactly. Thus two aspects of behaviour tally with our calculation as to what is optimal, but one does not. This conclusion is discussed.

Sleep postures and eye state of free-ranging herring gulls ( Larus argentatus ) were studied during the breeding season. Three mutually exclusive behaviours were observed, namely sleep, rest-sleep and rest postures. Arousal thresholds, eye blink rates and eye closure time were obtained during these behaviours. Significant relationships existed between eye blinking, eye closure, and a raised threshold of arousal when birds were in the sleep and rest-sleep postures. During a natural disturbance, birds in the sleep posture remained in this posture but did not blink their eyes: this is called pseudo sleep. Male gulls also exhibited a lower threshold of arousal while in the sleep posture compared with females. We conclude that rhythmic eye blinking is a good indication of sleep in herring gulls.

Food supplements placed daily beside the nests of herring gulls, Larus argentatus, for the first 5 days after the first chick hatched produced improved weight gains over this initial period and higher fledging success, particularly in the third chick. The fledging success of the fed group appears to be due to increased weight gain and not to increased parental protection in the supplemented period. Since there is indirect evidence that food is available this suggests that the parents are putting less effort into foraging for their chicks than they are able to, and less than is in the interests of the third chick, in the first days after hatching. On a separate colony we found that having three chicks in the brood for more than 5 days resulted in lower weight gains for the second chick, but not the first. We suggest that fledging three chicks rather than one or two greatly increases the parents' reproductive effort, and consequently interpret the third egg as primarily insurance against the loss of the first or second.

The feeding behaviour and movements of individually marked herring gulls at refuse tips were observed during the winters of 1973–1976. Refuse tips were used more by adult than by immature gulls. Adult female and immature gulls were more transient than adult males, changed their feeding sites more often, and used the secondary rather than the main feeding area of a tip more than the adult males. Individuals feeding in the main area fed at a higher rate and were involved in more aggressive encounters than those in the secondary area. Competition between adults and immatures, and a tendency for adult males to be the most dominant, brings about the dispersal between feeding sites of the adult females and the immatures.

Incubating herring gulls, Larus argentatus, quickly learned to operate feeding boxes placed on their territories. Subsequently, they were rarely observed to be absent from their territories and their nest-relief behaviour and incubation schedules differed significantly from that of a control group. Mates in the control group apparently adopted complementary feeding strategies and the relative abundance of an individual's preferred foods was correlated with its nest-relief behaviour.

The nest-relief behaviour of herring gulls Larus argentatus can be classified in terms of the apparent relative willingness of mates to undertake incubation duties. In this paper the nest-relief behaviour is described and its occurrence correlated with the availability of foraging opportunities. It appears that a conflict of interest arises when feeding opportunities occur, and that this is reflected in the nest-relief behaviour.

The results relating to agonistic behaviour obtained during an exploration of the brain of juvenile herring and lesser black-backed gulls ( Larus argentatus and fuscus ) with electrical stimulation are reported. As an introduction the normal agonistic behaviour of immature gulls is described. While the flight and aggressive behaviour is largely unritualized the threat behaviour is more stereotyped. Three basic threat patterns are distinguished: the arched, hunched, and squat postures. The relationship of these juvenile agonistic patterns with adult courtship is considered. A large number of sites evoking fear behaviour were found, anatomically widely and incoherently distributed. It is demonstrated that the spontaneous fearfulness levels of individual subjects influences the likelihood of obtaining escape eliciting loci. Stimulation of a nubmer of these sites had an after-effect: a persistent, increased probability of escape behaviour. It seems likely that a proportion of the fear sequences elicited were secondary responses to evoked sensory hallucinations and forced small movements. None of the sites explored yielded outright attack behaviour. Thirteen sites yielded characteristic threat sequences. About half of them produced changes in ‘mood’ persisting for some 15 min. The sites were clustered in a paleostriatal-septal periventricular and an infundibular area. Histological differentiation of the neuroventricular interface at these areas is noted. Based on these it is argued that the secretion of ‘liquormones’ is responsible for the changes in ‘mood’ that followed stimulation.