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Laughing gulls (Larus atricilla) are commonly found in many areas of North America and little is known about their diet, particularly in coastal-urban interfaces where gull-aircraft collisions can be a serious concern. The objective of this study was to describe and quantify the consumption of terrestrial invertebrates by laughing gulls at a coastal-urban interface in the northeastern United States. We examined the stomach contents of laughing gulls (n = 1053) collected during wildlife damage management operations at John F. Kennedy International Airport during the summers of 2003 and 2004. Terrestrial invertebrates consumed by laughing gulls represented 2 taxonomic phyla, 4 classes, 15 orders and 40 families. Beetles (Coleoptera) and ants (Hymenoptera) were the most common terrestrial invertebrates consumed by laughing gulls. We found evidence of temporal (i.e., monthly) variation in the frequency of occurrence of terrestrial insects in laughing gull diets. Laughing gull gender and age did not...

Forster's Terns (Sterna forsteri) often forage alone or within mixed- species foraging aggregations. We investigated the relative costs and benefits of these two foraging strategies. Metrics used to assess differences in strategies included the number of attempts for prey (both successful and missed), capture efficiency, and capture rate. Forster's Terns foraging socially cue on presence and behavior of other aggregating species, especially Snowy Egrets (Egretta thula). Joining aggregations significantly increased their capture rate, but not their capture efficiency, compared to solitarily foraging terns. However, total aggregation size, influenced primarily by the two most abundant species, Laughing Gulls (Larus atricilla) and Snowy Egrets, affected tern behavior. For example, diving terns often collided with Laughing Gulls, causing frequent missed attempts for socially foraging individuals. Thus, large aggregation sizes had a negative effect on foraging success, perhaps because of interference ...

Summary In 1969, 1500 pairs of terns Sterna spp. and 50 pairs of Laughing Gulls Larus atricilla nested on Petit Manan Island, Maine, U.S.A. The gulls formed groups of up to eleven individuals to steal fish from the terns. The start of piracy coincided with hatching of the gull's eggs. Larger groups more often succeeded in stealing fish than smaller groups. Group formation cannot be ascribed to rarity of terns to chase, and is not due to shared advantage in fish seized or time spent chasing (hence energy expended). A sufficient explanation is the individual advantage to some gulls that join a small group at the expense of the initiator. Individual gulls are likely to follow different strategies. Chasing appeared to be more readily elicited by a chase in progress than by a tern carrying a fish.

We recorded for the first time in Cuatro Cienegas Basin, Coahuila, Mexico, 43 species, 33 of them represented by specimens and 10 only by visual observations. These records increase the species known for the basin by 38.4%. The fieldwork was conducted during 1996 and 1997. Two species are new records for the state of Coahuila: Larus atricilla and Camptostoma imberbe.

The authors examined concentrations of lead, cadmium, mercury, manganese, selenium, and chromium in feathers, liver, kidney, heart, and muscle of known-aged laughing gulls (Larus atricilla) that hatched in Barnegat Bay, New Jersey and were collected at John F. Kennedy International Airport, New York 1 to 7 years later. Concentrations differed significantly among tissues, and tissue entered all the regression models explaining the greatest variation in metal levels. Age of bird contributed significantly to the models for lead, cadmium, selenium, and chromium. Although there were significant gender differences in all body measurements except wing length, there were few differences in metal levels. Males had significantly higher lead levels in feathers, and females had significantly higher selenium levels in heart and muscle tissue. For lead, 3-year olds had the highest levels in the heart, liver, and kidney, and levels were lower thereafter. Mercury levels in feathers and heart decreased significantly with age. Cadmium levels increased significantly with age for feathers, heart, liver, and muscle, although there was a slight decrease in the 7-year olds. Selenium levels decreased significantly with age for all tissues. Chromium levels increased with age for liver and heart.

Newly hatched laughing gulls, Larus atricilla , pecked at herring gull models more than at models of their own species, and preferred an unusual laughing gull model to a more conventional one. Chicks learned to peck preferentially at laughing gull models that fed them and to reduce their pecking at models that did not; they learned best when the model was unusual. Chicks were also able to learn to prefer a particular laughing gull mew call over a mew call recorded from a different laughing gull. When auditory cues were present during conditioning, the degree and importance of visual learning sharply declined.

The assessment of secondary poisoning is an important consideration in the hazard evaluation of predator control agents and rodenticide baits. The selection of an appropriate test animal model is difficult because classiclaboratory species are frequently inappropriate, and the availability and reliability of wild species for testing is limited. The laughing gull (Larus atricilla) has demonstrated its usefulness as a secondary poisoning model in the laboratory and shown species sensitivity through case history documentation of secondary poisoning mortality in the field. A number of new candidate rodenticides are being developed throughout the world for control of rodent pests in domestic, industrial, and agricultural marketplaces. Because one or more of these rodenticides could have a wide variety of outdoor uses, the effects of these substances on the environment must be evaluated in terms of both their toxicity and their exposure. The portion of that evaluation which is to be considered in this paper concerns the assessment of secondary poisoning of birds. utilizing the laughing gull as a model for an avian predator.

Massachusetts Maritime Academy (MMA) conducted a study to evaluate the potential impact of the MMA wind turbine (Vestas V47-660 kW) on birds, including common terns (Sterna hirundo), which are protected at the state level, and roseate (S. dougalii) terns, which are protected at the federal level. We found that common terns were relatively abundant on the water adjacent to the wind turbine, especially during the post-breeding period (7 Aug-30 Sep). Roseate terns, however, were much less abundant than common terns, and their presence at the study site was nearly limited to the chick-rearing period (19 Jun-6 Aug). Both species were least abundant during the nesting period (24 Apr-18 Jun). During the study, we observed 253 terns passing through wind turbine airspace (i.e., within 50 m of the wind turbine). Most (n = 226) were common terns, 1 was a roseate tern, and 16 were unidentified to the species level. Terns (all categories) were most abundant in wind airspace during the chick-rearing period, especially during morning hours (0530-1100). However, their abundance was dependent upon the operational status of the wind turbine rotor. Terns were less abundant in wind turbine airspace when the rotor velocity was >1 rpm than when the rotor velocity was

This investigation detailed the clinical disease, gross and histologic lesions, and distribution of viral antigen in juvenile laughing gulls (Larus atricilla) intranasally inoculated with either the A/tern/South Africa/61 (H5N3) (tern/SA) influenza virus or the A/chicken/Hong Kong/220/97 (H5N1) (chicken/HK) influenza virus, which are both highly pathogenic for chickens. Neither morbidity nor mortality was observed in gulls inoculated with either virus within the 14-day investigative period. Gross lesions resultant from infection with either virus were only mild, with the tern/SA virus causing decreased lucency of the air sacs (2/6), splenomegaly (2/6), and pancreatic mottling (1/6) and the chicken/HK virus causing only decreased lucency of the air sacs (2/8) and conjunctival edema (2/8). Histologic lesions in the tern/SA-inoculated gulls included a mild to moderate heterophilic to lymphoplasmacytic airsacculitis (6/6), mild to moderate interstitial pneumonia (3/6), and moderate necrotizing pancreatitis and hepatitis at 14 days postinoculation (DPI) (2/6). Immunohistochemical demonstration of viral antigen occurred only in association with lesions in the liver and pancreas. In contrast, viral antigen was not demonstrated in any tissues from the chicken/HK-inoculated gulls, and inflammatory lesions were confined to the air sac (3/8) and lungs (3/8). Both viruses were isolated at low titers (10(1.68) mean embryo lethal dose) from oropharyngeal and cloacal swabs up to 7 days postinoculation (DPI), from the lung and kidney of one of two tern/SA-inoculated gulls at 14 DPI, and from the lung of one of two chicken/HK-inoculated gulls at 7 DPI. Antibodies to influenza viruses as determined with the agar gel precipitin test at 14 DPI were detected only in the two tern/SA-inoculated gulls and not in the two chicken/HK-inoculated gulls.

On 15 May 2000, I observed a Laughing Gull (Larus atricilla) nest parasitized by a Black-bellied Whistling-duck (Dendrocygna autumnalis). The nest contained three Laughing Gull eggs and three Black-bellied Whistling-duck eggs and was located in a colony of 56 Laughing Gull nests.

I report avian behavioral responses to a total solar eclipse on the north coast of Venezuela during the afternoon of 26 February 1998. Magnificent Frigate-birds (Fregata magnificens), Brown Pelicans (Pelecanus occidentalis), and Royal Terns (Sterna maxima), which had been foraging over the water before the eclipse, left the bay 39 (terns) or 13 (frigate-birds and pelicans) min before the eclipse became total. The frigate-birds flew inland and the pelicans went to roosts on cliffs bordering the bay. Residents of the local village, who knew the birds' behavior well, remarked that the frigate-birds and pelicans were behaving as they normally did at sunset. Laughing Gulls (Larus atricilla) ceased foraging and flew rapidly back and forth over the water in a tight flock during the 3 min 40 s of totality. Twelve minutes after the solar disc emerged, the frigate-birds and pelicans began to return to the bay, and they and the gulls resumed foraging. The terns still had not reappeared more than 1 hr after totality. Solar eclipses, although of brief duration, apparently reduce light levels sufficiently to temporarily interrupt normal avian diurnal behavior.

The age at which female gulls first reproduce is poorly documented. We examined plumage and reproductive organs of Laughing Gulls (Larus atricilla) collected from May–August 2000–2001 at John F. Kennedy International Airport, New York, to determine age-specific reproductive effort. Each gull was classified as one year old (hatched in previous year), two years old, or ≥3 years old on the basis of color patterns of the hood and tail feathers and fifth primary flight feather. For females, each ovary was examined to determine if post-ovulatory follicles were present. In 2000 and 2001, the first gulls with postovulatory follicles were recorded on 15 and 18 May, respectively. Overall, 54% of the 211 two-year-old female Laughing Gulls collected during June–August showed evidence of egg laying compared to 88% of the 320 gulls ≥3 years old. None of the 50 one-year-old females examined showed evidence of egg laying. Although a lower proportion of two-year-old females laid eggs compared to older gulls, we f...

Although Laughing Gulls (Larus atricilla) in southern New Jersey nest in highly productive salt marshes, adults commonly forage at inland sites when they have young in the nest. Foods from these inland sites have much lower levels of salt than typical marine foods available near the breeding colonies. I hypothesized that Laughing Gulls optimize growth and survival of their offspring by selecting nestling diets that minimize the amount of salt intake. I investigated the role of dietary salt intake on growth of young by providing salt supplements to groups of nestlings in 2 experiments conducted in 1993 and 1994. Dietary salt supplements administered in 1993, but not in 1994, slowed nestling growth and resulted in lower final body weights, total head lengths, and exposed culmen lengths. Nestlings receiving lower salt supplements fared better. By feeding their chicks inland foods, adults may minimize osmotic stress for their young and thereby enhance their growth and survival. Received 19 May 1997, accepted 3 August 1997, final version received 27 August 1997.

We studied the behavior of gulls at night with an image intensifier telescope to determine whether they were active at night, and the extent of their foraging in coastal habitats of New Jersey in the summer, fall, and winter of 1989–1990. Regression models and Kruskal-Wallis tests indicated that date, time of day, tide, cloud cover, moon phase, and study location all influenced variations in the presence and nocturnal activities of gulls. For each site and species, an, average of 48–88% of the nocturnal surveys recorded gulls foraging or flying about. More laughing gulls (Larus atricilla) foraged at night at Brigantine Beach compared to ring-billed gulls (L. delawarensis) at the northern New Jersey sites. However, more gulls were flying about at the Raritan River site compared to the other places. We suggest that more laughing gulls fed at night compared to ring-billed gulls because the former were breeding. Breeding gulls spend half their time incubating or caring for chicks, and thus might have time constraints on foraging during the day. Laughing gulls foraged at all times of the night on some surveys, but were more frequent around midnight, and the number of flying laughing gulls decreased after 0200 hours. Ring-billed gulls, however, seemed to be equally active all night. Our data indicate that gulls can be active all night, and in all habitats.

After the eggs hatch, about 63% of the large eggshell fragments can be found near laughing gulls' nests. For the shells that were found, the mean distance from the rim of the nest was less than 80 cm at three study sites. The removal distance was positively correlated with the size of the nest platform, which suggests that birds often walk to the edge of the platform and simply drop the shell. Within the colony, eggshells have a natural variation in darkness that is related to the range of darkness of the nest material. In preference tests we have matched shell models to the darkness of the eggs in the nest. When both natural shells and orange shells pegged to the ground were presented simultaneously, gulls preferentially attempted to remove the orange shell. The strength of the preference for the pegged orange shell varied from site to site within the colony, so the results were validated in a separate experiment by placing shells in the nest bowl one at a time to be removed in as natural a manner as possible. Orange was stiff preferred; fear of the orange model seemed to promote the removal response. Contrary to the expectations from prior studies, the natural model was also no stronger stimulus than a solid white model in pegged shell tests. Control tests with white, grey, and black models indicate that brightness plays a very weak role, so the removal preference must be based on colour. When pegged models of any colour were on the nest and the bird engaged in nest building, the nest building was usually biased toward the models, but not precisely directed at them. Our results suggest that removal behaviour can be elicited via different perceptual mechanisms. One mechanism specifically recognizes the egg-shell, while the other mechanism is stimulated by a broad range of foreign objects that contrast with the nest background. In the laughing gull, the contrast mechanism appears to be at least as strong as the recognition mechanism. This may be related to the low level of predation experienced by these gulls.

1) Ink from the sea hare Aplysia dactylomela was examined to determine its possible role as a defensive mechanism by being distasteful to potential predators. 2) Feeding experiments were set up to determine the acceptance or rejection of various sections of Aplysia dactylomela and pieces of local baitfish (Mugil curema) containing Aplysia ink, to a population of laughing gulls (Larus atricilla). 3) Feeding experiments showed that Aplysia dactylomela ink was distasteful to laughing gulls. The gulls would reject pieces of baitfish which had been thoroughly coated with ink. The rejection rates by the gulls for baitfish injected with the ink was higher than the rejection rates towards certain parts of Aplysia, including those known to contain toxic material.

Confirming previous observations in the gull-colony the parental attraction-call 'crooning' selectively enhanced activity while the alarm-calls 'kow' and 'uk-uk' suppressed activity and vocalizations, even in the absence of additional visual clues. These calls may have had the observed effects in part because of certain acoustic characteristics to which chicks preferentially respond and in part because of specific experiences that chicks may have had with these calls prior to testing. Some of the difference between experiment (a) and (b) in the performance towards 'uk-uk' calls may have been due to the fact that the chicks in (b) were tested later in the season than the chicks in (a). Later hatching chicks may have been physically less well developed and thus less responsive than earlier hatched chicks, or they may have had differential kinds or amounts of auditory experience before they were tested. The present results differ from findings of an earlier pilot-investigation (BEER, 1973) in which recordings of single adult birds evoked no clearcut responses in chicks. However most of those chicks had been several days old and in other experiments it was shown that responsiveness to calls of adults changes with age (BEER, 1970b).Observations. Adult Laughing Gulls utter several distinct calls during the incubation of their eggs and the raising of their chicks. One call referred to as 'uhr' call is frequently heard during incubation in conjunction with rising from the eggs or resettling, and in response to the mate's activities near the nest. 'Crooning' is heard during mate-reliefs in incubation. After hatching this call functions to attract the young to the parent. `Uk-uk' and 'kow' alarm-calls are both uttered when the colony is disturbed by a potential predator, but 'kow' calls can also be heard in purely conspecific disturbances. Experiment I . The responses of day-old chicks, reared by their parents, were investigated towards recordings of some of these calls. Confirming observations in the wild, `crooning' selectively enhanced activity and elicited approach; 'uk-uk' suppressed activity and vocalization and elicited crouching; 'kow' calls had similar effects but to a lesser extent. Experiment 2. Chicks collected at hatching from nests in the gull-colony were compared with chicks hatched in an incubator in order to discover whether the prenatal conditions affected early postnatal responsiveness to 'crooning'. It was found that parent-hatched chicks showed increased activity in the presence of 'crooning' and some of them approached the speaker, whilst incubator-hatched chicks were not activated by these calls. Experiment 3. Younger chicks were compared with older chicks (all hatched in the incubator) for the purpose of finding out to what extent their responsiveness to 'crooning' would change with postnatal age. The results showed that to parentally inexperienced chicks this call increasingly acquires the effects of alarm-calls in that it suppresses vocalization and activity and elicits crouching. Experiment 4. The role of parental calls as experienced in the wild during incubation was examined experimentally. During the last 2 1/2 to 3 days of incubation eggs were repeatedly exposed to different types of calls (or no calls at all), in order to see to what extent and with what degree of selectivity such exposures would affect responsiveness to 'crooning' and 'kow' calls in newly hatched chicks. It was found that prenatal exposure to 'crooning' leads to enhancement of activity and vocalization in the presence of such calls postnatally. Effects of prenatal experience with disyllabic 'uhr' call point into the same direction. Prenatal experience with 'kow' calls does not lead to early postnatal activation in response to 'crooning'. Responsiveness to 'kow' calls was only affected by prenatal exposure to these calls. Discussion. Some previously published studies in this field of research are briefly reviewed and compared with the present findings. The relative contribution of prior experience of parental and filial vocalizations to later responsiveness to parental calls is discussed. Earlier research in the Laughing Gull had shown that parentally inexperienced embryos are selectively activated by 'crooning' till close to hatching. In the present study it was shown that repeated prenatal experience with 'crooning' leads to its attractiveness after hatching. Therefore repeated prenatal (and maybe early postnatal) exposure to this call and related calls seems to function to maintain and. consolidate responsiveness to this call in the neonate. In contrast to 'crooning', 'kow' alarm-calls heard prenatally do not enhance nor suppress motility. Prior exposure to this call does not maintain this apparent indifference, but merely reduces the extent to which it acquires activiy suppressing effects.

Lead concentrations were measured in eggs, prefledgings and adult laughing gulls collected near Galveston, Texas. No lead was found in eggs. Prefledgling and adult birds had lead ranging from zero to 16 mug/g wet tissue. Liver had the greatest lead concentrations followed by brain, heart and skeletal muscle. There were no significant differences in lead concentrations between fledglings and adults or between males and females.

Hailman reported that wild-reared laughing gull, Larus atricilla, chicks peck preferentially at models of laughing gulls over models of herring gulls, L. argentatus, but newly hatched chicks have no species preference, and respond equally well to an isolated red bill. The experiments reported here confirm these observations. They also suggest that the pecking of newly hatched chicks is guided by heterogeneous summation. A new working definition of heterogeneous summation is presented. Furthermore, the results suggest that species preference does not develop spontaneously with maturation or on the basis of imprinting, but rather from reinforcement and conditioned inhibition or habituation. It appears that learning can take place only to a model with high releasing value for pecking, and that the crooning call of adult laughing gulls has no major effect on pecking in newly hatched chicks.

Predation by laughing gulls, Larus atricilla , on black skimmer, Rynchops niger , chicks was observed in a Texas nesting colony. The patterns of predation differed from random in two respects: (1) significantly more attacks (both attempts and successes) were directed toward nests with two parents present than toward nests with only one parent and (2) significantly more attempts occurred when female parents were brooding than males. Differences in gull attack rates according to sex of the parent skimmer may have been due to the considerable sexual size dimorphism in skimmers. Male skimmers are larger than laughing gulls, while female skimmers are smaller. Predation on skimmer eggs was uncommon. Solo incubating by females was significantly less frequent after the first egg's hatching than before. The decreased frequency of female solo attendance after the first hatching may represent an adaptive response to predator pressure at a time when chicks are most vulnerable to predation by gape-limited predators such as laughing gulls and would be better protected by males or both parents. The higher observed frequencies of both predation attempts and successes directed toward nests with bi-parental attendance was not predicted and may be attributable to certain unavoidable high risk activities, such as brooding exchanges and chick feeding when broods are young, which typically occur only when both parents are present.

Laughing gulls Larus atricilla , nesting in saltmarshes subject to tidal inundations, build substantial nests and continue adding material throughout the reproductive cycle. Under normal conditions, nest size increased until gulls had 5-day-old chicks. I manipulated nests at various stages in the reproductive cycle. Until their chicks reached 14 days of age, gulls added material to artificially wetted nests, making them significantly deeper and wider than before treatment. During all reproductive stages examined, gulls repaired nests having half of the material removed. The adaptive significances of nest building and relative nest size are discussed in terms of washouts and the requirements of the eggs and chicks at different stages in the reproductive cycle.

We recorded the choice of victims by a population of adult and first-winter laughing gulls ( Larus atricilla ) making attempts to steal food from adult and juvenile brown pelicans ( Pelecanus occidentalis ). Adult gulls made food theft attempts on juvenile pelicans with a disproportionately great frequency; first-winter gulls appeared to select pelican victims at random. Adult pelicans were more frequently successful in their foraging attempts than juvenile pelicans, suggesting that adults may be more reliable as potential food sources for gulls making theft attempts. However, juvenile pelicans attempted to evade kleptoparasitizing gulls less frequently than did adult pelicans, suggesting that the fish prey of juveniles may be more easily stolen. These patterns are discussed in relation to optimal victim choice by gulls, and to deferred maturity in both species.

Laughing Gulls (Larus atricilla) were studied in a tidal salt marsh located in Brigantine, New Jersey and on an island in the Gulf of Mexico to determine how nesting gulls respond to conspecific intruders. Gulls were observed in Texas and at Brigantine during the pre-egg stage. In Texas, Laughing Gulls set up pairing territories in the sand beach area next to the colony, and defended these areas against conspecifics. In New Jersey, pairing territories were often located on Spartina mats within the colony area. Twelve pairs of gulls were marked, sexed, and observed for eight to fourteen hours per day during the incubation period. An intruder was defined as any gull other than the nesting pair which landed within three meters of the nest. The interactions between the nesting pair and intruders were recorded for 1145 sequences. Eighty-five percent of all intruders were responded to with the following patterns: Long Calls (18%), Intruder Displays (45%), and Chases (22%). Long Calls and Intruder Displays were given by an incubating bird, while Chasing was performed by the mate standing nearby. Gulls flying over the nest were usually reacted to with a Long Call although Intruder Displays were sometimes given. Intruders landing within one meter of the nest were always given an Intruder Display by the incubating bird and were frequently chased by its mate. Intruders landing from one to two meters from the nest were usually given the Intruder Display: those landing two to three meters from the nest were usually chased. Gulls landing over three meters from the nest were usually ignored. The probability that an intruder was responded to decreased as the distance from the nest increased. The behavior of intruders was as follows. Fifty-three percent of the intruders landing within a meter of the nests were rapists or potential rapists. These intruders remained on the nest longer than did other intruder, and sometimes evoked pecking and attack from the incubating bird. Nest-material stealers (18%) remained on the nest for less time. Neighbors (7%) infrequently landed on the wrong nest but quickly flew to their own nest. In 22 percent of the cases the activities of the intruders could not be determined, since they were quickly repelled.

laughing gulls emit a call referred to as ‘crooning’ with increasing frequency shortly before the hatching of their young. Uttered to newly hatched chicks this call appears to enhance pecking for food. The adult birds ‘kow’ call in response to disturbances near the nest. Incubator raised chicks respond differentially to these two calls, both pre- and post-natally. An experiment was designed to discover whether the hearing of such vocalizations prenatally would have any bearing on their postnatal effectiveness in eliciting pecking. With respect to ‘crooning’ an effect was found but it would not be clearly demonstrated that ‘crooning’ heard prenatally enhances pecking. Chicks pecked less often when hearing ‘kow’ calls regardless of prenatal experience with this call.

Three age-groups of laughing gull chicks were tested with playback of recordings of calls of their parents and calls of neighbouring adults. The chicks in each group showed response to the playback calls, and recognition of the voices of their parents. The chicks in the early group (1 to 3 days post-hatching) showed the least evidence of parent recognition: the chicks of the late group (12 to 28 days post-hatching) showed the lowest levels of response in general. Evidence of relationships between variation in the behaviour in the tests and variation in the test recordings was found from correlation analysis, the type of call initiating positive response, and analysis of temporal association. This evidence, and the results of tests which allowed responses to the parents' crooning and responses to the parents' ke-hah calls to be compared for chicks in the late group, indicate that whereas the filial approach behaviour of very young chicks is stimulated by crooning but suppressed by ke-hah and long-calls, this behaviour in older chicks requires the occurrence of ke-hah calls or long-calls for its elicitation. However the ke-hah calls and long-calls of adults other than the parents continue to have negative effects on the behaviour of older chicks. It is argued that this progression in discrimination of the voices of the parents and the changes in responsiveness to the different types of adult calls are consistent with functional requirements, both from the point of view of changes in a growing chick's social situation and from the point of view of the characteristics of the calls. The changes are also discussed from a developmental point of view.

Twelve matched pairs of parent-raised and hand-raised laughing gull chicks from the same clutches were tested, at 6 to 8 days post-hatching, with successive presentations of playback of a recording of calls of their parents and recording of calls of parents from a neighbouring nest, in a situation in which they could approach or withdraw from the sound. The parent-raised chicks oriented towards the sound, moved towards the sound and called when the calls of their own parents were played; they tended to withdraw from the sound and sit silently when the calls of the neighbouring parents were played. The hand-raised chicks fled from the sound and crouched in silence in response to both calls of their parents and the calls of neighbours. They were more vocal and active in periods without sound than were the parent-raised chicks. It is concluded that laughing gull chicks in nature learn to recognize the individual characteristics of the calls of their parents, and to react positively to the calls, through interaction with their parents prior to the age of 6 days post-hatching.

THERE are scattered records in the literature showing that the weights of consecutively laid fresh eggs or their measured lengths and maximum diameters may either decrease or increase in different species. In a statistical analysis of 20 clutches in the Laughing Gull (Larus atricilla), Preston and Preston (1953) showed that the length measurement did not differ significantly either among the eggs of the same clutch or between the eggs of different clutches. On the other hand, in three-egg clutches the third egg laid had a significantly smaller diameter than the first two. In two-egg clutches, the second egg appeared to resemble the third more than the second in the three-egg clutches, but the small number of measurements available did not permit definite conclusions. Since a large series of data had been collected at the Baldwin Bird Research Laboratory, near Cleveland, Ohio, between 1925 and 1938, on the eggs of the House Wren (Troglodytes aedon), we decided to determine whether or not there were any consistent changes in dimensions and weight with sequence of laying in this passerine species.

Observations on Laughing Gulls suggest that calls emanating from pipping eggs are responsible for several behavioural changes typical for the transition from incubation to parental behaviour. In order to study the role of vocalisations unconfounded by tactile stimuli provided by pipping eggs, calls recorded from a hatching chick were played to incubating birds from underneath the nest-cup and their effects were observed. Incubating gulls responded to such calls by an increase in the frequency of the following behaviour patterns: looking down, rising-resettling, shifting the eggs, quivering while sitting and calling. Qualitatively new, parental behaviour patterns were not quantitatively recorded, but were seldom observed in response to the calls. In contrast to earlier experiments with tactile stimuli, nest-material manipulations and the proportion of incomplete settling movements were not significantly affected by these auditory stimuli. An inverse relationship was found between the strength of responsiveness to chick-calls and the number of nest-building movements performed during the experiment. Tests carried out at different stages of the incubation period revealed that the responsiveness to chick-vocalisations increases as a function of progressing incubation. A preliminary experiment was performed to test for the selectivity of the response. Incubating birds responded more strongly to the calls played to them at normal speed than at half the speed (which changes the calls' pitch, frequency modulation and temporal characteristics).

Lead and cadmium concentrations were measured in eggs and in bone, kidney, liver and stomach contents of downy young, prefledgling, and adult Laughing Gulls collected from Matagorda Bay and Galveston Bay, Texas. Matagorda Bay drains a rural, moderately industrialized region while the Galveston Bay area is heavily urbanized and industrialized. Lead levels were lower in birds from Matagorda Bay and decreased in birds from Galveston Bay between 1977 and 1980. Cadmium levels were also lower in birds from Matagorda Bay but increased over the three-year period in those from Galveston Bay. The temporal decrease in lead may be associated with such environmental control efforts as reduced point source emissions and substitution of unleaded gasoline.

The frequency of long-calling in untreated and hormone-treated juvenile laughing gulls was compared. While both estrogen and testosterone increased the calling rate, testosterone was more effective for both sexes. Both estrogen- and testosterone-treated males called more often than similarly treated females. As both sexes normally call in laughing gulls, these results were compared to the more usual situation where only males of the species sing. Possible control mechanisms were discussed.

Larus atricilla [spec. nov.] L. albus, capite alarumque apicibus nigris, rostro rubro. Larus major. Catesb. car. 1. p. 89. t. 89. Habitat in America., Published as part of Linnaeus, Carolus, 1758, Systema Naturae per regna tria naturae: secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis, Stockholm :Laurentius Salvius on page 136, DOI: 10.5962/bhl.title.542, http://zenodo.org/record/3922206

Kuken der amerikanischen Lachmowe (Aztekenmove,Larus atricilula), die in dunklen Brutkasten schlupfen, picken bei farblosem Hintergrund mehr nach roten oder blauen als nach grunen oder gelben Attrappen. Farblose (schwarzweisse) Attrappen losten dagegen vermehrtes Picken gegen grunen oder gelben Hintergrund aus als gegen einen roten oder blauen. Die Farbbevorzugung ist also spiegelbildlich. Mogliche Deutungen des Wahrnehme-Mechanismus werden diskutiert.