Gull Nests Research Articles

Intensive Predation of Artificial Audouin's Gull Nests by the Yellow-Legged Gull in the Columbretes Islands, Spain

Intensive Predation of Artificial Audouin's Gull Nests by the Yellow-Legged Gull in the Columbretes Islands, Spain

Nest-Site Selection and Reproductive Success of Ring-Billed Gulls at Sprague Lake, Washington

AssTRAcr-Nest-site selection and reproductive success are reported for ring-billed gulls nesting at Sprague Lake, Washington, in 1981. Gulls nesting in tall grass and rocky beach habitats began laying significantly earlier than other gulls. Incubation times also varied by location, with birds in peripheral areas spending over three days longer to incubate their eggs than those nesting in the main part of the colony. Reproductive success was highest for birds nesting in tall grass, followed by those in rocky beach, sparse vegetation, low dense herb, and peripheral areas, respectively. Nest densities by habitat were determined in 1979, 1980, and 1981. Densities were highest in tall grass, followed by those in rocky beach, sparse vegetation, and low dense herb, respectively. Associated California gulls nested almost exclusively in sparse vegetation. Nests with supernormal clutches (5-6 eggs) were more common in sparse vegetation, low dense herb, and peripheral areas than in tall grass and rocky beach and accounted for 0.9% of the ring-billed gull nests in the colony.

Nest predation and nest site selection among EidersSomateria mollissima:the influence of gulls

Hooded Crows Corvus cornix, Great Black‐backed GullsLarus marinusand Herring Gulls L. argentatus were the main nest predators in an Eider population in southwest Sweden. The clutch sizes of Eider nests within gull colonies did not differ from those outside gull colonies. The proportion of Eider nests destroyed by predators was significantly lower within than outside gull colonies, especially on islands with Lesser Black‐backed Gulls L. fuscus. Although the difference was not significant, the survival time of simulated Eider nests was higher within than outside gull colonies. On Eider islands with gull colonies, foraying crows spent more time within the colony area than expected by chance. However, crows apparently avoided an area around each gull nest, and we suggest that the colonies, to some extent, protected Eider nests against predation. The density of Eider nests was higher on gull islands than on gull‐ free islands, and higher within than outside the gull colonies. However, the association with gulls was weak compared to that displayed by some other waterfowl.

Secondary Sex Ratios and Egg Sequence in Herring Gulls

Variation in the secondary (hatching) sex ratio has been documented for many bird species. Significant deviations from the 1:1 ratio have led to theoretical speculation about adaptive facultative manipulation of the sex ratio (Trivers and Willard 1973). Seasonal changes in the nestling sex ratio of the Common Grackle (Quiscalus quiscula; Howe 1977) and the Redwinged Blackbird (Agelaius phoeniceus; Fiala 1981) and the biased production of male Zebra Finches (Poephila guttata; Burley 1981) by females mated with highquality males provide some support to the TriversWillard hypothesis. Recently, Ankney (1982) found that in newly hatched Lesser Snow Geese (Chen caerulescens) the first two eggs of 4-egg clutches produced more males (64%) than females and the last two eggs produced more females (72%) than males. Similarly, Ryder (1983) reported in Ring-billed Gulls (Larus delawarensis) the first-laid eggs of 3-egg clutches hatched predominantly more males (66%) than females and the second-laid eggs hatched more females (61 %) than males. This phenomenon suggested a facultative manipulation of the sex produced, although the adaptive significance is unexplained. Weatherhead (1985) examined the occurrence of a sex-sequence relationship in the Red-winged Blackbird after Fiala's (1981) documentation that the last-laid egg of this species produced significantly more females than males. Although Weatherhead (1985) found a sex-sequence relationship, the pattern was not consistent among different clutch sizes. Stimulated by these studies, we examined the secondary sex ratio in relation to laying sequence in newly hatched Herring Gull (L. argentatus) chicks on Granite Island (48?43'N, 88?29'W) in Black Bay, northern Lake Superior (see Ryder 1976 for a description of the colony). During the 1983-1986 nesting seasons, newly constructed Herring Gull nest sites were marked numerically with spray paint and the nests checked daily for the presence of new eggs. Each egg in a clutch was marked in sequence laid by placing dots of nail enamel on the blunt end of the egg (1 dot = first egg laid, 2 dots = second, 3 dots = third). The latest date we arrived at Granite Island was 11 May in 1983. We thus used 11 May as the standard date to compare the progress of Herring Gull egg laying in the three nesting seasons (1984 data were not available). Close to the expected time of hatching, nests were checked twice daily for signs of pipping eggs. Chicks hatched from 3-egg clutches were collected and their sex determined by gonadal inspection. We used only those clutches from which all eggs hatched and where the position of each chick in the sequence laid was known for statistical analyses. We compared clutch sizes using ANOVA and Scheffe a posteriori tests. The sex-ratio data were analyzed using Chi-square and G-tests (Sokal and Rohlf 1981). Significance was accepted at P < 0.05. Upon our arrival at Granite Island each year, laying in several nests had already commenced. The difference in the proportions of initiated and completed clutches by 11 May each year (Fig. 1) indicates that Herring Gulls breeding in 1983 did so later in the season than those nesting in 1985 and 1986. The proportion of nests with 3 eggs was much lower in 1983 than in the other years (Table 1). This low 3-egg clutch-size frequency was manifested in the significantly lower average clutch size for 1983 (F = 5.02, P < 0.05). The secondary sex ratio favored females in 1983 and 1985 and males in 1984 and 1986 (Table 2). The deviation from a 1:1 sex ratio, however, was not significant in any of these years. The G-statistic also indicated no significant relationship between sex and sequence for any year. Similar results were obtained from the combined data. Our results suggest that the allocation of sex chromosomes by the heterogametic female Herring Gull is a random process. A late season, lower average clutch size and hatch of 12% more females than males occurred in 1983. Although it was tempting, at first, to invoke the predictions of the Trivers-Willard (1973) hypothesis, whereby the later-starting females may have been in relatively poor physiological condition

Observations on the breeding biology of Sabine's Gulls (Xema sabini)

The breeding biology of Sabine's Gulls (Xema sabini) nesting in a colony with Arctic Terns (Sternaparadisaea) was studied in 1980 at East Bay, Southampton Island, N.W.T. Sabine's Gull nests were initiated over a 1.5-week period, from 23 June to 3 July, and the mean clutch size was 2.77. The mean weight of freshly laid eggs was 22.3 g. Hatching was asynchronous and occurred from 14 to 22 July, following an incubation period of 21 days. Of 53 eggs laid, 44 hatched (83.0%). Chicks showed typical sigmoidal patterns of growth for weight, culmen, and tarsus, and a straight line pattern for ninth primary feather. Growth was rapid, and chicks attained nearly adult proportions by 13 to 15 days of age. The timing and duration of the breeding effort (just over 7 weeks) and the rapid rate of growth of Sabine's Gull chicks are seen as adaptations to the short Arctic summer. The mean internest distance between Sabine's Gulls on the colony was 92.5 m. Nesting was more dense on islands than on the mainland, reflecting the attractiveness of sites least accessible to mammalian predators. An apparent association between breeding Sabine's Gulls and Arctic Terns is reported and two explanations are offered: first, a reliance by Sabine's Gulls on the aggressive behaviour of Arctic Terns or second, coincidence.

Adaptations of Migratory Shorebirds to Highly Saline and Alkaline Lakes: Wilson's Phalarope and American Avocet

Wilson’s Phalaropes (Phalaropus tricolor) and American Avocets (Recurvirostra americana) occur in large numbers at hypersaline and alkaline lakes. Comparing birds from three lakes of different salinity and alkalinity in the Great Basin of western North America, we found no evidence of salt-loading: blood hematocrit, pH, osmolality, and sodium concentration were not elevated; stomach osmolality and sodium concentration were only slightly higher than the body fluids of the birds’ hypo-osmotic prey (brine shrimp and brine flies); salt glands were not enlarged and averaged a relatively low percentage of body weight (0.02%). Through a combination of behavioral and anatomical adaptations, phalaropes and avocets evidently are able to rid their prey of most adherent lake water and thereby largely avoid the problems of salt-loading and the ingestion of harmful ions. Both species occupy hypersaline habitats for long periods and probably derive most of their water needs from the body fluids of their prey. Their use of fresh water is sporadic and may not be required for osmoregulatory balance. Alkaline and hypersaline lakes, despite being harsh physical environments, are prime habitats for a few species of resident (e.g., flamingos) and a somewhat larger number of migratory waterbirds. Mono Lake, California, a large hypersaline (2’ 12 x the concentration of sea water) and alkaline (pH x 10) lake at the eastern base of the Sierra Nevada, attracts large numbers of a few of these species each year. Approximately 45,000 California Gulls (Larus californicus) nest there; in summer and in fall, tens of thousands of Wilson’s (Phalaropus tricolor) and Red-necked (P. lobatus) phalaropes stop over on their southward migration (Jehl 198 l), and hundreds of thousands of Eared Grebes (Podiceps nigricollis) stage there (Storer and Jehl 1985). American Avocets (Recurvirostra americana) are also common at hypersaline lakes, although at Mono Lake only a few pairs breed and flocks of several hundred occur in autumn. Hypersaline lakes are attractive to these birds because they typically lack fish, which allows the few invertebrates that can occupy them to attain great abundances. These, in turn, serve as food for the birds. At Mono Lake, brine shrimp (Artemia sp.) and brine flies (Ephydru hians) become super-abundant at some seasons. Birds feeding on these invertebrates, either by pecking them from the surface of the water or by catching them while driving, might be expected to ingest large amounts of lake water and thereby incur deleterious salt loads. Yet, our previous studies of California Gulls (Mahoney and Jehl 1985a) and Eared Grebes (Mahoney and Jehl 1985b) at Mono Lake, where salinities have varied from 72 to 90 ppt (2,160-2,700 mOsm/kg) in 1982-l 984, have shown that this is not the case. These species seem to have no special anatomical or physiological adaptations for dealing with high salt loads. Instead, they largely avoid osmoregulatory problems behaviorally, by ridding their food of adherent lake water before swallowing it. Gulls and grebes differ markedly in their use of fresh water. Gulls visit freshwater streams to drink and bathe several times each day, whereas grebes, although they may remain continuously at Mono Lake for as long as six months (Jehl, unpubl. data), never visit fresh water. Wilson’s Phalaropes and American Avocets (Fig. 1) have intermediate patterns of water use; both visit fresh water regularly, though probably not daily. If phalaropes and avocets ingest large quantities of Mono Lake water and its attendant osmotic and ionic load, they could be expected to show changes in blood chemistry, hydration state, and salt gland size. In order to determine how great a salt load these birds incur while feeding at the lake, we made the following measurements: blood pH and hematocrit; serum osmolality, sodium, and potassium; composition and osmolality of stomach contents, prey body fluids, and lake water; body water content; and salt gland weights. We then compared these values from Mono Lake birds to those

Nest Site Selection by Laughing Gulls: Comparison of Tropical Colonies (Culebra, Puerto Rico) with Temperate Colonies (New Jersey)

We examined nest site selection in Laughing Gulls (Larus atricilla) nesting on three islands in the Culebra National Wildlife Refuge, Puerto Rico, to determine if gull nest sites showed consistent characteristics differing from most of the available habitat, to compare nest site characteristics on islands with different vegetative cover, and to contrast nest site choices on these tropical island colonies with colonies that we have studied on the northern Atlantic coast of mainland United States. At Culebra, Laughing Gulls nested with Royal, Sandwich, and Bridled terns (Sterna maxima, S. sandvicensis, S. anaethetus), Brown Noddies (Anous stolidus), and Brown Boobies (Sula leucogaster), but their nearest neighbors were usually conspecifics. The gulls' nest sites generally differed from random points with respect to percent cover, vegetation height, visibility, and distance from clearings. Compared to the random points, gull nests were under denser vegetation of intermediate height with high visibility from their nests and with less cover around their nests. Their choice of nest sites provided protection and cover from predators and the sun. Dense and tall vegetation would hinder gulls from flying directly from their nests, and many nests were thus near rocks or clearings, which allowed the gulls to exit quickly. Laughing Gulls nesting on the Culebran cays generally nested in taller, denser vegetation than those nesting farther north along the Atlantic coast, which partially reflects temperature differences between the localities.

Note complémentaire sur l’utilisation de l’espace chez l’Avocette Recurvirostra avosetta

In the «Parc Ornithologique du Marquenterre» young avocets leave their nest 24 hours after the hatching of the first young of the brood. This is much earlier than usually reported by other observers (72 hours). This early dispersal is probably due to the high density of nests in the park (36 avocet nests on a 450 m² islet, and 2 nests of Black-headed gulls) leading to strong competition for food and space.

Laughing Gull Nest Placement on Little Pelican Island, Galveston Bay

Laughing Gull Nest Placement on Little Pelican Island, Galveston Bay

Effect of Date on Counts of Nests of Herring and Lesser Black-Backed Gulls

Effect of Date on Counts of Nests of Herring and Lesser Black-Backed Gulls

Colonial breeding reduces nest predation in the common gull ( Larus canus)

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.

The effects of nesting gulls on the vegetation and soil of islands in the Great Lakes

The effects of nesting colonies of the Ring-billed Gull (Larus delawarensis Ord.) on vegetation and soil nutrients were monitored over a 4-year period on Barrier Island and other islands in Georgian Bay and Lake Huron, in the Great Lakes region of Canada. Nesting had a profound effect on the vegetation and species composition. Two distinct communities of annual alien species dominated the nesting sites, one flowering in May and June and the other from late August to October. Native species were rare in the nesting sites, in contrast to adjacent areas, where perennial native grasses were dominant. Factors favouring the replacement of indigenous vegetation by annual aliens include physical disturbance by gulls during nesting and deposition of guano, which caused dramatic increases in the levels of soil nutrients. Plant succession in nesting sites that had been abandoned for 3 and 4 years was characterized by a rapid decline in the abundance of annual aliens and their replacement by perennials. After the 2nd year native perennial grasses were dominant. Nutrient levels in the soil rapidly returned to near normal, except for phosphorus, which persisted at high levels. Herring Gull (Larus argentatus Pontoppidan) nests were also studied. Their density was much lower, and hence their effects were less pronounced. However, they supported a similar annual alien flora. Herring Gulls frequently nested on unvegetated cobble or gravel shores where the humus from the nests permitted the establishment of a permanent vegetation.

The Selective Importance of Heat Stress in Gull Nest Location

A brief but intense heat wave on 9 June 1979 caused catastrophic chick mortality in a population of Western Gulls on Santa Barbara Island, California, USA. Mortality ranged from 0 to 90%o in different areas of the colony. Mortality was not a function of the amount of vegetation cover available to chicks, nor did chick age or size affect the probability of mortality during the heat wave. In the absence of a heat wave, chick mortality due to heat stress is rare in this population. Microclimate analysis in 1980 showed that the area of high chick heat stress mortality in 1979 was characterized by higher ground and air temperatures and lower wind velocities than the area of low mortality. Taxidermic thin metal chick models had a higher integrated thermal load, or operative environmental temperature, in the area of previous high mortality. The persistent nesting by gulls in areas of high potential chick mortality cannot be explained by habitat shortage or by the competitive inferiority of those birds. Enhanced access to food resources may explain the persistence of one area, but not of several others. Analysis of long-term weather records for the southern Channel Islands region showed that heat waves during the breeding season are rare: of nine possible heat waves in 62 yr of data, five have occurred since 1973. The present nesting distribution of gulls on the island has probably not evolved in a regime of frequent heat waves, but rather in response to a long period of highly equable climatic conditions.

Size Selective Hunting by Slaty-backed Gulls Larus schistisagus and Influence on Fledging Success of Black-tailed Gulls L. crassirostris

(1) The influence of predation by Slaty-backed Gulls Larus schistisagus on the fledging success of Black-tailed Gulls L. crassirostris was studied on Teuri Island off Haboro, Hokkaido, in 1980 and 1981. (2) Four quadrats were set in the breeding colony of Black-tailed Gulls in which 326 chicks were colour ringed and their biomass was measured. The analysis of food remains collected from forty nests of Slaty-backed Gulls was made for the estimation of the amount of predation. (3) The amount of predation reached a maximum later than the time when the biomass of prey reached a maximum. (4) Slaty-backed Gulls selectively hunt smaller chicks because of low hunting successs of large prey. (5) Later broods of Black-tailed Gulls were exposed to higher predation pressure by Slaty-backed Gulls. (6) The fledging success of Black-tailed Gulls was lower in late (14%) than in early (31%) and middle broods (41%). This trend could partly be explained by predation by Slaty-backed Gulls.

Foraging-Flock Recruitment at a Black-Billed Gull Colony: Implications for the Information Center Hypothesis

Foraging-Flock Recruitment at a Black-Billed Gull Colony: Implications for the Information Center Hypothesis

Reproductive Performance of Ring-Billed Gulls in Relation to Nest Location

-We evaluated the reproductive performance of Ring-billed Gulls (Larus delawarensis) nesting on the periphery and in the center of a colony in northern Lake Superior in 1976 and 1977. The center and periphery of this colony were not subject to flooding, predation or differential human disturbance. Egg-laying, clutch size, hatching and fledging success, and nest attentiveness did not differ significantly between and clutches. The colony population has increased in size during the last five years and become stabilized, whereby and areas are now being occupied simultaneously. In this study, reproductive performance was related more to the timing than the location of nesting. The proportion of eggs hatched and young fledged often differ markedly in relation to nest location in colonies of many bird species. Birds nesting in the part of a colony normally hatch proportionately more eggs and raise more young than do birds with nests on the periphery (Coulson 1968, Dexheimer and Southern 1974). We wanted to determine if such differences existed at an island colony of Ring-billed Gulls (Larus delawarensis) that has shown a rapid increase in size in recent years. STUDY AREA AND METHODS We conducted the study during the nesting seasons (May, June, July) of 1976 and 1977 on Granite Island (48043'N, 88029'W), Black Bay, northern Lake Superior. Granite Island is a rock outcrop 402 m by 201 m with a summit 30 m above the surrounding water. During the study the colony consisted of 1,900 pairs. The nesting habitat was described by Ryder and Somppi (1977). The nesting area was on the summit of the island. The gulls nested in numerous shallow depressions in the granite rock surface. The dominant vegetation in the depressions was Kentucky bluegrass (Poa pratensis). The area formed the south and west edges of the area and consisted of the same type of habitat. Immediately adjacent to the area, off the colony, was a forest, primarily of balsam fir (Abies balsamea), white cedar (Thuja occidentalis), and white birch (Betula papyrifera). No gulls nested in the forest. We use the following terms: a peripheral nest was located on the edge of the colony, forming part of the border (Dexheimer and Southern 1974) and not surrounded by other nests. A central nest was located inside the border of the colony and was surrounded by other nests (Tenaza 1971). Hatching was the percentage of eggs laid that hatched (Gilman et al. 1977). Fledging was the percent of chicks that were estimated to fledge from eggs hatched (Gilman et al. 1977). A fledgling was a chick at least 21 days old (Dexheimer and Southern 1974). Reproductive was the number of chicks fledged per breeding pair. Daily nest histories were kept in 1977 for all clutches within the study area. We did not visit the colony during the hottest part of the day or during inclement weather because we assumed that such visits would hinder the survival of embryos. Nests were marked with a numbered wooden block placed beside the nest. Eggs were numbered, in the sequence they were laid, on the blunt end with a non-toxic felt pen. In 1977 we measured the distance to nearest neighbor for a total of 98 randomly chosen nests in order to assess the relationship of nest spacing to reproductive performance. Chicks were marked at hatching with a numbered fingerling fish tag fastened through the foot web. We recaptured them at 7 to 14 days of age, when their legs were large enough to retain a U.S. Fish and Wildlife Service aluminum leg band. To facilitate recovery of the chicks, we erected a 30.5-cm fence of chicken wire mesh around the study area. Nisbet and Drury (1972) found that the effect of this type of fencing on breeding success was negligible in their study of Common Terns (Sterna hirundo) and Roseate Terns (S. dougallii). Additionally, they stated that Pearson (1968) and Langham (1968) had fenced Arctic Tern (S. paradisaea) and Black-headed Gull (L. ridibundus) nests, respectively, without detrimental effects. We monitored attentiveness of early-nesting gulls in the center and periphery of the colony in both years using a camera mounted in a 5.5-m high observation tower located just off the colony. The camera was equipped with an automatic timer set for one shot every 3 min. In 1976, we determined from the film the presence or absence of attendants during early, mid and late incubation from 25 and 25 nests that were started during the peak of egg-laying. In 1977 this procedure was repeated for 30 early and 24 early nests. Additionally, in 1977 we recorded attentiveness at 16 late-starting nests and eight late-starting nests.

A Balance for Weighing Ground-Nesting Birds

SUMMARY A nest balance for weighing incubating birds repeatedly in the field has been success- fully used with herring gulls (Larus argentatus) and barnacle geese (Branta leucapsis). Three methods of recording data from the balance are discussed. Periodic weighing of animals is easily and profitably performed in the laboratory but is often more difficult in the field. The technique presented here allows the weight of a bird to be calculated during the incubation season by placing its nest on a tray on a balance buried in the ground from which remote readings of weight may be made. Successful calculation of the weight of the bird depends on knowing the weight of the nest. This may be obtained directly when the bird leaves the nest, or indirectly by allowing for changes in moisture content of the nest that have occurred since an earlier measurement. The construction of the balance is shown in Figs 1 and 2. The accuracy of the system depends critically on four factors: that the centre-lines of the springs be equidistant from the centre-line of the potentiometer, that the springs and the flexible coupling hang vertical, that the springs have the same elasticity, and that the length of the flexible coupling be unaffected by moisture. Twelve balances were made and were found to have a linear response over a 5 kg range, with a standard deviation about the regression line of approximately 15 g (range 7-30), which represents the limiting accuracy of the balances we constructed. Balances were assembled and calibrated prior to use. Installation of a balance beneath a nest takes about an hour, and with care can be done with little change visible to the human eye. The first few feet of the cable leading from the potentiometer to the recorder were buried. In 1976 ten, and in 1977 nine balances were placed under herring gull (Larus argentatus) nests in a fenced study area in the large mixed colony of herring and lesser black backed gulls (L. fuscus) on Walney Island, Cumbria. Measurements were taken auto- matically every 5 min by data-logger in a cottage 200 m from the birds. To correct for variation in moisture content one balance was loaded with an artificial nest and the amounts of nest material on the other balances were adjusted to be roughly the same. The operation of the balances was checked and lost eggs were replaced by fresh ones once a day.

Wad Medani and Soldado Viruses from Ticks (Ixodoidea) in West Africa1

A total of 2282 ticks representing at least 12 species was collected in Senegal and Mauritania during 1977 and tested for virus in suckling mice. Wad Medani virus was recovered from 8 lots of Rhipicephalus guilhoni and 1 lot of R. e. evertsi collected from domestic animals. Soldado virus was isolated from 14 lots of Ornithodoros capensis taken from debris in nests of Grey-headed Gulls (Larus cirrhocephalus).

Breeding habitat use by colonially nesting waterbirds in two mid-atlantic US regions under different regimes of human disturbance

More than 80% of the beach-nesting seabirds (common tern, least tern, black skimmer, and herring gull) in coastal Virginia nest on natural barrier island beaches, while in New Jersey the vast majority nest on dredge deposition material or natural marsh islands. This contrast probably results from the differences in human disturbance in the two regions. Although 75% of all oceanfront in New Jersey allows unrestricted recreation, about 85% of the Virginia beaches are ‘protected’ under the ownership of several conservation agencies. Attendant with changes in habitat utilisation in New Jersey, competitive interactions have apparently intensified with herring gulls usurping tern and laughing gull nest sites. Other implications are discussed.

Competition and Predation: Herring Gulls versus Laughing Gulls

Gulls of the genus Larus generally nest colonially, often in mixed-species assemblages. For example, Herring Gulls (L. argentatus) in Europe nest with Lesser Blackbacked Gulls (L. fuscus; Brown 1967, MacRoberts and MacRoberts 1972) and Black-headed Gulls (L. ridibundus; Greenhalgh 1974); and in North America Ringbilled Gulls (L. delawarensis) nest with California Gulls (L. californicus; Vermeer 1970) and Herring Gulls (Southern 1970). It is often difficult to determine whether such assemblages are actually mixed, or if monospecific colonies simply exist side by side. When assemblages are mixed it is often impossible to ascertain whether they are so by choice or because of a lack of suitable nest sites. The rate of competition and predation by one or both species has not been investigated. In this paper I examine competitive interactions and predation between Laughing Gulls (L. atricilla) and Herring Gulls on Clam Island, New Jersey, from 1976 through 1978. Laughing Gulls on the east coast of the United States traditionally nest in Spartina salt marshes (Bent 1921), although at the limits of their range they frequently nest on dry land (Nisbet 1971, Dinsmore and Schreiber 1974). Thus, when Herring Gulls expanded southward in the early 1900's into Maine and Massachusetts, they came into direct conflict with Laughing Gulls (Nisbet 1971, Drury and Kadlec 1974). As early as 1943, Herring Gulls nested with Laughing Gulls in a sand dune colony at Muskeget Island, Massachusetts (Noble and Wurm 1943). Despite initial differences in habitat, the Laughing Gulls disappeared (Nisbet, pers. comm.). Increases in Herring Gulls in the northeast also have been associated with decreases in Common Terns (Sterna hirundo; Nisbet 1973). In the 1950's and 1960's Herring Gulls again expanded their breeding range, nesting as far south as North Carolina with Laughing Gulls (Hailman 1963, Parnell and Soots 1975). They nested on the upper parts of domes on man-made islands while Laughing Gulls occupied low swales between the domes. Where Herring Gulls were absent, Laughing Gulls nested farther up the domes (Parnell and Soots 1975). When Herring Gulls began breeding in more southern areas, they chose to nest in salt marshes, the customary nesting areas of the large and stable Laughing Gull colonies (Burger 1977). Although differences in nest site selection were noted initially, these differences decreased as Herring Gull colonies expanded. Overlap in colony and nest site characteristics is obvious in several New Jersey colonies (Burger and Shisler 1978). Since the first report of Herring Gulls on Clam Island (Rogers 1965), the colony has increased from 50 to 1,200 pairs whereas the Laughing Gull colony of 4,000 to 6,000 pairs remained about the same size through 1976. My primary objectives in this paper are to examine how these species interact temporally and behaviorally, and to determine the result of these interactions in terms of nesting space allocation and reproductive suc-