Studies in Avian Biology No. lO:l-7, 1987.

GULL RESEARCH IN THE 1980s: SYMPOSIUM OVERVIEW

WILLIAM E. SOUTHERN'

Symposia are now a regular feature of the an- providing for mans’ environmental require- nual meetings of scientific organizations. Two ments, we must possessan in-depth understand- approaches are available for selecting themes for ing of the speciesinvolved, including their breed- symposia. The subject may be a concept, such ing biology, habitat requirements, food habits, as the mechanisms of bird orientation, and re- and long-term responses to environmental searchers working on an array of species present change. The papers presented in this symposium results tied together by the unifying conceptual contribute significantly to the development of a thread. The other option is to use a taxon as the data base that is essential for resource managers. common denominator and have the investi- In addition, many of the papers address more gators discuss a variety of concepts as they apply theoretical aspectsofbehavioral ecology for which to one or more closely related species. Both types gulls are ideal subjects because of their colonial of symposia have their advantages. The orga- nesting habits and their tendency to use nest sites nizers of the 1985 First Joint Meeting of the accessible to investigators. Pacific Seabird Group (PSG) and the Colonial Gulls as a group also have served as the sub- Waterbird Group (CWG) considered it an ap- jects of basic research that has contributed to the propriate time to review the status of gull re- formulation of many major biological concepts. search in the 1980s. Presented herein are 11 pa- Such studies have expanded our understanding pers and 10 abstracts reflecting current larid of motivational systems (Tinbergen 1953, Baer- research and the approaches investigators are ends and Drent 1970), evolutionary behavior taking. (Moynihan 1958a & b, Beer 1975), physiology Gulls stand out as appropriate subjects for con- (Tucker 1972, Howell et al. 1974), foraging be- sideration at a scientific meeting because of their havior (Andersson et al. 198 1, Curtis et al. 1985, relationship with man in the past, present and, Greig 1984, Patton 1986), territoriality (Burger more than likely, in the future. During the nine- 1984), interspecific associations (Gotmark and teenth century egging activities, the feather trade, Andersson 1980, Barnard and Thompson 1985), reduction in fish populations, use of nearshore life history strategies (see Burger et al. 1980), and islands for livestock grazing and other human a number of other subjects. Because several gull endeavors lowered gull populations in North species have been thoroughly studied, it is now America (Graham 1975). Protection in the form possible to design interesting comparative stud- of state, national and international legislation ies dealing with ecology and behavior. Even with early in the twentieth century resulted in gradual all the attention gulls have received from in- population increasesuntil about midway through vestigators, many unanswered questions remain. this century. Then there was a continent-wide The papers and abstracts presented in this vol- explosion in the population of several gull species ume provide an outstanding indication of the (e.g., Drury and Kadlec 1974, Ludwig 1974). En- directions gull research is taking and suggest ap- vironmental changes that probably made these proaches for further inquiry. population changes possible included the intro- Twenty-one species of gulls breed in North duction of forage fishes (smelt and alewives) in America and three other species regularly visit the Great Lakes, the operation of large landfills the continent (Farrand 1983). Of the five genera throughout the winter ranges of North American involved, Laws includes the largest number of gulls, construction of dredge-spoil islands, and species(19). Both species of Rissa occur here and the construction of new resting habitat (numer- Rhodostethia, Xema and Pagophila each are rep- ous ponds and reservoirs) throughout the ranges resented by one species. Several species range of some species. widely over arctic waters or are nearly pelagic in In the 1980s gull populations have become the North Atlantic and Pacific oceans. Six of the large or concentrated enough to result in conflicts 21 breeding species tend to nest in inland loca- with man. The increase in competition between tions whereas 15 species are primarily coastal gulls and man has added a practical component nesters. During the nonbreeding period, consid- to gull research. In order to develop management erable overlap occurs in the ranges of the non- strategies that are resource sensitive while also arctic species. The breeding ranges, however, are more distinct and only occasionally do more than two or three species share colony sites (Southern

’ ’ Department of Biological Sciences, Northern Illinois University, 1980, American Ornithologists ’ Union 1983). DeKalb, IL 60115. Several species of gulls are good research sub- 2 STUDIES IN AVIAN BIOLOGY jects because their colonies are relatively acces- sensitivity to these factors will result in more sible and they nest in large numbers which allow accurate data collection and analysis, and con- investigators to obtain statistically important clusions that more correctly describe how a given samples. During the last two decades alone, species is performing. (1) Gull investigators are hundreds of papers have been published about becoming increasingly cognizant of the impor- gull migration and orientation, seasonal distri- tance of long-term studies (e.g., Mills 1973, Coul- bution, breeding biology, sex ratios, ecology, food son and Thomas 198 5) which take into account habits and population size. Of the 21 species what happens throughout a particular breeding breeding in North America, 6 have received most season as well as throughout the lifespan of in- of the research attention: Laughing Gull, L. atri- dividual gulls. This is particularly applicable in cilia; Ring-billedgull, L. delawarensis; California the case of studies dealing with population trends, Gull, L. californicus; Herring Gull, L. argentatus; reproductive success and habitat selection. (2) Western Gull, L. occidentalis; and Glaucous- The project designs and methods used by many winged Gull, L. glaucescens. Others such as the researchers clearly show that they are now cog- kittiwakes (Rissa spp.), have been studied thor- nizant of the effects of investigator-caused dis- oughly in the Old World. Considerably less is turbance in gull colonies (Hunt 1972, Robert and known about others (e.g., Franklins’ Gull, L. pi- Ralph 1975, Hand 1980, Fetterolf 1983). Ignor- pixcan; Bonapartes’ Gull, L. Philadelphia; Mew ing these effects when designing or conducting a Gull, L. canus; Iceland Gull, L. glaucoides; Ross ’ study can seriously bias the data collected, par- Gull, Rhodostethia rosea; Sabines’ Gull, Xema ticularly in studies measuring chick survivor- sabini; and Ivory Gull, Pagophila eburnea). ship, parental care, aggressiveness and territo- Bents’ (1947) “Life Histories” illustrates the riality. (3) Methods of marking gulls may nature of gull research prior to the middle of this influence the accuracy of data collected and se- century. Shortly thereafter, Tinbergens’ (195 3) riously bias the outcome of a study. For example, classic study of the Herring Gull stimulated nu- Southern and Southern (1985) showed that wing merous ethological studies and field experi- markers detrimentally influence the breeding be- ments. Moynihan (195 8a & b) described the vi- havior of Ring-billed Gulls. Use of this marking sual and auditory displays of several larid species method during studies dealing with mate fidelity, and provided the types of information consid- longevity, site tenacity or other studies requiring ered necessary for an ethogram. Such studies pro- unimpeded return to the site of marking should vided us with significant descriptive information be avoided. It is no longer possible for investi- but they also caused us to de-emphasize the im- gators to discount the possibility that their ex- portance of individual differences in behavior. perimental methods may influence the behavior The fixed action pattern concept of Lorenz (see of their research subjects. Ways of avoiding such translations, 1970) left the impression that much complications must be developed during the of bird behavior was inflexible. We now know planning stages rather than attempting to work that more plasticity exists in the performance of around them statistically during the analysis stage. gull displays and the components of other be- The topics covered by this volume are some haviors than earlier investigators proclaimed. For of those having the greatest importance to larid example, gull chicks can stimulate adults to feed researchers today. The papers and abstracts are them by pecking at portions of the the bill other grouped into five subject areas: life histories, be- than the salient spot or ring that adults possess. havior, foraging, habitat selection and hybrid- Also, as parental care progresses during the nest- ization. Information of these types is accumu- ing season, experienced parents may attempt to lating gradually for most gull species. Particular feed without any begging by the chick (Hender- ones are more thoroughly studied than others but son 1975; pers. obs.). Experienced parents and sufficient data exist for a comparative approach chicks show more variability in the behaviors possibly relating the similarities and differences associated with parental care than do novice par- to morphological characteristics, ecological vari- ents and their chicks. These raw materials for ables associated with differing geographical behavioral change are awaiting the influences of ranges, and the effects of sympatry. The recent selective pressures and they should be catalogued work of Hoffman (1984) is an outstanding ex- by investigators (e.g., Hand 1979). Documenting ample of the value of the comparative approach. the variability in behavior, rather than ignoring Components of life history and ecological char- it in favor of the sample mean, may provide us acteristics of speciesare more difficult to describe with insight into the rate at which shifts in be- quantitatively than skeletal features; however, havioral tendencies may occur. someone needs to accept the challenge and syn- Gull researchers have contributed to at least thesize the behavioral and ecological data for three recent findings that have influenced the way gulls, particularly sympatric species. Burger that avian field research is conducted. Researcher (1980) stands out as a major contributor of n-77 r r..-.“_ 1 T.,-.TT *.r bULl_ KCXZ.AKLH II\ THE 198Os- Southern 3 species-specific data as well as a synthesizer of laid) commonly reported for gulls and suggests interspecific strategies. that it may not represent an adaptation for brood The 11 full-length papers in this volume are a reduction. Instead he considers it a non-adaptive significant contribution to gull biology. The ab- consequence of energy shortages during laying. stracts describe studies we will learn more about He also points out that asynchronous hatching in the months to come as the associated papers in gulls may be an adaptation for maximal growth are published. Following are some of my reac- rather than an adaptation for food stress. The tions to these papers. The abstracts are not dis- pattern of hatching in some gull species such as cussed because of space limitations and the in- the Ring-bill, however, is variable with some ability of the reader to refer to the full paper for clutches hatching all 3 eggs on the same day but details. hatching in others is spread over 2-6 days (Clark The lead paper by Walter V. Reid examines and Wilson 198 1; Southern, in prep.). Reids’ ex- factors that may limit clutch size in the Glau- planation, therefore, is not generally applicable cous-winged Gull. As with most Larus gulls, the to all gull species. clutch size of this species usually is limited to 3 D. Michael Fry, C. Kuehler Toone, Steven M. eggs, with 4 or more eggs being relatively infre- Speich and R. John Peard examine the factors quent, or associated with female-female pairs affecting skewed sex ratios in gulls, a subject that (Conover 1984). Several hypotheses have been has received considerable attention during the presented to account for the high frequency of last decade. Sex ratios skewed toward females 3-egg clutches. The energetic cost of egg forma- are thought to result female-female pairs (Hunt tion has been offered as one explanation for egg and Hunt 1977, Ryder 1978, Ryder and Somppi and clutch size in gulls (e.g., Boersma and Ryder 1979, Conover 1984). This phenomenon is in- 1983). Measuring weight gains or foraging suc- dicated by the occurrence of supernormal clutch- cessof individual gulls after they reach the breed- es (SNC) and indexed by the SNC percentage ing range may not be the best approach for ex- within a colony. Causes of skewed sex ratios may amining this possibility, although it is regularly be multifaceted as the authors describe. The find- used. More important may be the body condition ing that there is a decrease in the number of male of females when they arrive on the breeding gulls and an increase in the number of SNCs in grounds. Not infrequently, gulls spend relatively areas polluted with organochlorines is extremely little time foraging during the early stages of the interesting. Once again we are reminded that all nesting cycle (i.e., prelaying; pers. obs.). It ap- behavioral, morphological and physiological pears, therefore, that fat reserves may not only conditions we identify when examining large contribute to survival at this time but may pro- samples of organisms, as is possible in gull col- vide some of the energy required for egg pro- onies, are not necessarily adaptive (Gould and duction by early nesters. Ryder (pers. comm.) is Lewontin 1979, Hand 1979). Some, such as fe- investigating whether or not this may be the case male-female pairing, may not be indicative of a for Ring-billed Gulls. new mode of parental care that can be expected Reid suggestedthat the incubation capacity of to sweep through gull colonies, although some gulls may impose an upper limit on clutch size. investigators seemed to imply this in the past No evidence exists, however, to show that pos- (e.g., Hunt and Hunt 1977). session of only 3 brood patches prevents gulls Egg predation by conspecifics is not uncom- from successfully incubating more than 3 eggs mon when pair members are nesting asynchro- (Vermeer 1963, Coulter 1973), although Coulter nously from most of the colony or when they are (this symposium) showed that hatching success casual about attentiveness (pers. obs.). This is is highest for 3-egg clutches. The brood-rearing especially true of gulls with small nesting terri- capability of parent gulls has been suggested as tories. Attentive behavior by both sexes of par- another factor possibly responsible for limiting ents during incubation and early stages of chick clutch size (Haymes and Morris 1977), although development appears to be an effective defense some gulls are capable of rearing more than three against this form of predation (L. A. Hanners young (e.g., Coulter, this symposium). In spite MS; Shugart and Fitch, abstract this sympo- of this, average reproductive successseldom ex- sium). Individual differences occur, however, in ceeds 1.5 chicks per pair (Blokpoel and Tessier the performance of parental care by gulls and 1986) and may be considerably lower. It is likely this may contribute to differential brood success. that no single factor is responsible for the prev- Ralph D. Morris examines time-partitioning of alence of 3-egg clutches in gulls. The multiple clutch and brood care activities as measures of hypothesis approach of Winkler (1985) shows parental quality in Herring Gulls. His findings the advantages of a broader perspective to ques- confirm that pairs displaying the greatest syn- tions such as this. chrony in parental care produce the most young. Reid also calls attention to the small c-egg (third The subject of survivorship and mortality is 4 STUDIES IN AVIAN BIOLOGY fundamental to understanding the dynamics of dividual level and the concept of inclusive fitness avian populations and associated life history was applicable. Although earlier studies pro- strategies. According to Larry B. Spear, Harry R. duced evidence supportive of these contentions, Carter, Teresa M. Penniman, Jay F. Penniman the results from recent ones, including those of and David G. Ainley, only four studies provide Joseph G. Galusha and Ronald L. Carter pre- reliable information on survival rates in adult sented here, indicate that recognition may not gulls. These authors also report finding no quan- be well perfected in gulls and that adoptions or titative estimates of the various causes of mor- temporary care of young other than a parents’ tality that affect gull age or sex composition. Their own may occur (Holley 198 1, 1984; Spear et al. paper points to one of the areas of gull research 1986). This raises some interesting evolutionary that requires further attention by investigators. questions, including the significance of unin- Especially needed are reliable techniques for pre- tended cooperation in breeding gulls. In studies dicting changes in gull populations on a regional without investigator or other disturbances, chick basis and for cataloging the factors which limit mortality often is not a consequence of chicks population growth of these successfulgeneralists. invading neighboring territories. Some adults Gull populations have increased dramatically show varying levels of tolerance or acceptance across the Northern Hemisphere during recent of chicks other than their own. The result often decades thereby providing opportunities for in- is temporary or permanent adoption (Southern, vestigations of the causes and effects of such in prep.). Selective advantages to acceptance of changes. Conditions responsible for these signif- chicks by neighbors could exist, particularly in icant population changes are not restricted to a the case of gulls with small territories. Our skep- single region nor to a single species. Interesting ticisms about group selection should not close biological questions are associated with these our minds to such possibilities as the benefits population changes and the resulting inter- and may be at the individual level. The conclusion intra-specific conflicts. Arie L. Spaans, Alle A. of Galusha and Carter that adult gulls do not N. de Wit and Marianne van Vlaardingen ex- recognize their chicks individually but accept or amined the effects of increased population size reject them on the basis of their behavior de- on Herring Gull breeding success in The Neth- serves careful attention by other investigators. erlands. Between 1968 and 1984, the increase in Short-term and long-term adoptions also occur Herring Gull population size was more than five- regularly in Ring-billed Gulls (pers. obs.). A pos- fold. In the authors ’ study plots, the increase was sibility worthy of testing is that acceptance of three-fold with a corresponding decrease in the “foreign” chicks, particularly by experienced pairs number of young fledged per pair. Interestingly, that have lost their own chicks, contributes to under these conditions, experienced breeders were colony stability during a particular nesting cycle producing most of the offspring and the breeding by keeping more adults at the colony. If social schedule had advanced 49 days since the 1960s. facilitation has any importance to breeding gulls, Gulls are breeding earlier in other parts of the particularly those with small territories, assuring world as well. For example, since 1975 the onset an optimally sized social assemblage may be se- of hatching of Ring-billed Gulls at Rogers City, lectively advantageous. Michigan, has advanced 7-l 0 days with the first As information about gull species increases, it chicks now hatching in mid-May (Southern, in becomes increasingly important to synthesize the prep.). It is possible that the factors associated data and present an overview of what is typical with this shift involve more than density-depen- as well as what is unique to individual species dent phenomena, as suggestedby Spaans and his or groups of species. Joanna Burger presents a co-workers for Herring Gulls. Possibly subtle paper that accomplishes this goal using data she changes in temperate zone climatic conditions collected for 15 species of gulls in North Amer- are having a gradual affect. Other circumstances ica, Africa, Australia and Europe. Few investi- such as rising Great Lakes and ocean water levels gators have had such vast experience with the may be a further reflection of such changes. worlds’ gull species. Although an assortment of The subject of parental recognition of their authors cited by Burger have discussed the age- young has received the attention of several in- related differences in feeding ability, she is the vestigators working with various species of gulls first to use uniformly collected data to examine (e.g., Tinbergen 1953; Beer 1970, 1979; Miller foraging efficiency for a large number of widely and Emlen 1975). Intuitively it would seem that distributed gull species. Her results solidify the ground nesting colonial gulls with potentially theory that delayed maturation is likely to occur mobile young should possess some method for in cases where foraging difficulties exist. distinguishing their young from those of nearby The responses of nesting gulls to nocturnal conspecifics. At least this would be the case if predators and the effects of predators on breeding natural selection was occurring at only the in- successare subjects of broad interest to gull re- GULL RESEARCH IN THE 198Os- Southern 5 searchers (L. Southern et al. 1982). Joseph R. productive output. It appears that gulls continue Jehl and Charles Chase III discuss the foraging to use sites long after the habitats that existed patterns and prey selection of predators, espe- when they selected them no longer are evident. cially Great Homed Owls (Bubo virginianus) on In this volume, Raymond Pierotti examines the California Gulls. As in other studies (e.g., South- behavioral consequences of habitat selection in em et al. 1985), the authors found that adult gulls Herring Gulls. He compares the time budgets, left the colony during owl attacks. As a result, rates of aggressive behavior and diets of gulls indirect chick losses were a regular occurrence. nesting in three different habitats in Newfound- The hunting patterns of owls were regular and land. His results demonstrate that habitat choice predictable. Adult losseswere low but chick loss- may influence the type and frequency of partic- es occasionally were great. This study provides ular behaviors which, in turn, influence repro- further evidence that the “antipredator” behav- ductive success. Studies such as this which ad- ior of gulls, particularly under nocturnal condi- dress the variability within a population or species tions, is little more than avoidance by leaving are extremely important. Variation appears to be when predators are present. If adults make any the rule rather than the exception, particularly attempt to protect their offspring at night, it is when we are dealing with gulls because so many ineffective against most persistent nocturnal exhibit high levels of plasticity in behavior. From predators (see Southern et al. 1982 for a review). the evolutionary standpoint, tomorrows’ trends Jehl and Chase also provide important infor- exist in todays’ variability. It is well documented mation about who gets killed and why, which that behavioral changes can occur over relatively has implications for habitat selection and colony short spans of time. Devoting more attention to siting. Because the impact of predators can be such things as how variability in habitat pref- local but severe, sampling methods in large col- erence influences the production of offspring may onies must be considered carefully. give us a better record of evolution in progress. Considerable attention is being directed at the By studying hybridization in nature, it is pos- topics of habitat and nest-site selection by gulls. sible to assessthe evolutionary status of closely Kees Vermeer and Kevin DeVito compare the related populations (Moore 1977). If members characteristics of sites selected by Mew Gulls and of two populations successfully and freely inter- Glaucous-winged Gulls. Information about the breed whenever their ranges overlap, taxono- Mew Gull is especially interesting as this species mists should seriously consider classifying them has been little studied in North America. On as conspecifics (Hoffman et al. 1978). Hybrid- Vancouver Island about 80% of the Mew Gulls ization occurs between many of the large Lams nested as solitary pairs. Nest sites frequently were gulls (Tinbergen 1953, Ingolfsson 1970, Jehl on the tops of poles or other objects which were 197 1). In this volume, Aonar Ingolfsson, who is surrounded by water. The Glaucous-winged Gull, recognized for his long-term studies of gulls in on the other hand, is primarily a colonial nester. the far north, presents information collected over Interspecific plasticity in nest site selection by 15 years about the extensive hybridization be- both species was noted. tween the Herring and Glaucous gulls in Iceland. Habitat selection has received considerable at- Herring Gull-like birds raised fewer young per tention from gull biologists, and justifiably so nesting attempt that more Glaucous Gull-like (Bongiomo 1970, Burger and Shisler 1978, Er- individuals. Birds of intermediate appearance had win et al. 198 1, Montevecchi 1978). A common a higher incidence of non-breeding than the oth- flaw in many such studies, however, is that the ers. It appears that the population in this area is investigator assumes that the conditions under not becoming more Glaucous Gull-like, possibly which gulls may be nesting when a study starts as a result of continuing immigration of pure are the same as those that existed when individ- Herring Gulls from Europe. ual gulls first occupied the site. Changes in cover A variety of topics is discussed in this volume. type and density may occur within a breeding I am confident that you, the reader, will find them season because of plant growth and even more stimulating as well as a significant contribution dramatic changes may occur over the lifespan of to the gull literature. Ernst Mayr (1984) vividly individual gulls. Since nest site tenacity is well portrayed the contributions ornithologists have documented in gulls (L. Southern, in prep.), as made to biology. It is clear that we are continuing is mate fidelity, the probability exists that given to make progress. Our understanding of the ap- nest sites will change over time because of plant propriateness of techniques, the importance of succession or other variables. Long-term studies long-term studies, and our attention to the effects are necessary to distinguish between the effects our own activities may be having on the accuracy of nest site selection and effects associated with of our data, will enable gull biologists to make plant successionor other time-related factors (i.e., even greater contributions in the future. time vs. tradition) on an individuals’ total re- This volume is the first joint publication of the 6 STUDIES IN AVIAN BIOLOGY

Pacific Seabird Group and the Colonial Water- in the biology of the kittiwake Rissa tridactyla:a 3 l- bird Group and originated at their First Joint year study of a breeding colony. J. Anim. Ecol. 54: Meeting. We hope this achievement will stim- 9-26. ulate further cooperation between two organi- COULTER,M. C. 1973. Clutch size in the Western Gull. Ibis 115:474. zations which together can have profound influ- CURTIS,D. J., C. G. GALBRAITH,J. C. SMYTH,AND D. ence on colonial waterbird and seabird B. A. THOMPSON.1985. Seasonalvariations in prey conservation and management in this hemi- selectionby estuarineBlack-headed Gulls (Lams ri- sphere and worldwide. dibundus).Est. Coast. Shelf Sci. 21:75-89. DRURY,W. H., ANDJ. A. KADLEC. 1974. The current status of the Herring Gull population in the north- LITERATURE CITED eastern United States. Bird-Banding 45:297-306. AMERICANORNITHOLOGISTS UNION.’ 1983. Check- ERWIN,R. M., J. GALLI, AND J. BURGER. 1981. Col- list of North American birds. Sixth Edition. Allen ony site dynamics and habitat use in Atlantic coast Press, Lawrence, KS. seabirds.Auk 98:550-561. ANDERSSON,M., F. GOTMARK, AND C. WIKLUND. FARRAND,J., JR. 1983. The Audubon Societymaster 1981. Food information in the Black-headedGull, guideto birding. Vol. 2, Gulls to dippers.A. A. Knopf, Larus ridibundus.Behav. Ecol. Sociobiol.9: 195-200. New York. 398 pp. BAERENDS,G. P., ANDR. H. DRENT. 1970. The Her- FETTEROLF,P. M. 1983. Effectsof investigator activ- ring Gull and its egg. Behav. Suppl. 17:l-3 12. ity on Ring-billed Gull behavior and reproductive BARNARD,C. J., ANDD. B. A. THOMPSON.1985. Gulls performance. Wilson Bull. 95:23-4 1. and Plovers, the ecology and behaviour of mixed- GOTMARK,F., AND M. ANDERSSON.1980. Breeding speciesfeeding groups. Columbia Univ. Press,New associatesbetween Common Gull (Larus cams) and York. 302 pp. Arctic Skua (Stercorariusparasiticus). Omis Stand. BEER,C. G. 1970. On the responseof Laughing Gull 11:121-124. chicks (Lams atricilla) to the calls of adults. I. Rec- GOULD,S. J., AND R. C. LEWONTIN. 1979. The span- ognition of the voices of parents. Anim. Behav. 18: drels of San Marco and the Panglossianparadigm: 652-660. a critique of the adaptationist programme. Proc. R. BEER,C. G. 1975. Multiple functions and gull dis- Sot. London B 205:581-598. plays. Pp. 16-54, in G. P. Baerends,C. G. Beer, and GRAHAM,F., JR. 1975. Gulls, a social history. Ran- A. Manning (eds.). Functions and evolution of be- dom House, New York. 179 pp. haviour. Clarendon Press, Oxford. GREIG,S. A. 1984. The feeding behaviour of Lams BENT,A. C. 1947. Life histories of North American argentatusand other Larus gulls at refuse tips. Un- gulls and terns. Dodd, Mead & Co., New York. 333 publ. Ph.D. thesis, Univ. of Durham. PP. HAND,J. L. 1979. Vocal communication ofthe West- BLOKPOEL,H., AND G. D. TESSIER.1986. The Ring- em Gull (Larus occidentalis).Unpubl. Ph.D. disser- billed Gull in Ontario: a review of a new problem tation, Univ. California, Los Angeles, CA. species.Occas. Paper No. 57, CanadianWildlife Serv., HAND, J. L. 1980. Human disturbance in Western Ottawa. 34 pp. Gull Larus occidentalislivens colonies and possible BOERSMA,D., ANDJ. P. RYDER. 1983. Reproductive amplification of intraspecific predation. Biol. Con- performance and body condition of earlier and later serv. 18:59-63. nestingRing-billed Gulls. J. Field Omithol. 54:374- HENDERSON,B. A. 1975. Role of the chicks’ begging 380. behavior in the regulation of parental feeding be- BONGIORNO,S. 1970. Nest-site selectionby Laughing havior of Lams glaucescens.Condor 77:488-492. Gulls (Lams atricilla). Anim. Behav. 18:434-444. HOFFMAN,W. 1984. Phylogeny, feeding behavior, BURGER,J. 1980. The transition to independenceand and wing structure in gulls, terns, and allies (Laro- postfledgingparental care in seabirds.Pp. 367-447, idea). Unpubl. Ph.D. dissertation,Univ. South Flor- in J. Burger, B. L. Olla, and H. E. Winn (eds.). Be- ida, Tampa, FL. havior of marine animals,Vol. 4. Plenum Publ. Corp., HOFFMAN,W., J. A. WIENS,AND J. M SCOTT. 1978. New York. Hybridization between gulls (Larus glaucescensand BURGER,J. 1984. Pattern, mechanism, and adaptive L. occidentalis)in the Pacific northwest. Auk 95: significanceof territoriality in Herring Gulls (Larus 441-458. argentatus).Om. Mono. No. 34, A.O.U., Washing- HOLLEY,A. J. F. 1981. Naturally arising adoption in ton, DC. 92 pp. the Herring Gull. Anim. Behav. 29:302-303. BURGER,J., B. L. OLLA,AND H. E. WINN (eds.). 1980. HOLLEY,A. J. F. 1984. Adoption, parent-chick rec- Behavior of marine animals, Vol. 4. Plenum Publ. ognition and maladaption in the Herring Gull (Lams Corp., New York. argentatus).Z. Tierpsychol. 64:9-14. BURGER,J., ANDJ. SHISLER.1978. Nest site selection HOWELL,T. R., B. ARAYA,AND W. R. MILLIE. 1974. and competitive interaction of Herring and Laughing Breedingbiology of the Gray Gull, Larus modestus. gulls in New Jersey. Auk 95:252-266. Univ. Calif. Publ. Zool. 104:1-57. CLARK,A. B., ANDD. S. WILSON. 1981. Avian breed- HUNT, G. L., JR. 1972. Influence of food distribution ing adaptations:Hatching asynchrony,brood reduc- and human disturbanceon the reproductive success tion, and nest failure. Quart. Rev. Biol. 561253-277. of Herring Gulls. Ecology 53: 1051. CONOVER,M. R. 1984. Occurrence of supernormal HUNT, G. L., AND M. W. HUNT. 1977. Female-female clutchesin the Laridae. Wilson Bull. 961249-267. pairing in Western Gulls (Larus occidentalis)in COULSON,J. C., AND C. S. THOMAS. 1985. Changes southern California. Science 196:1466-1467. GULL RESEARCH IN THE 198Os- Southern 7

INGOLFSSON,A. 1970. Hybridization of Glaucous human disturbanceon the breeding successof gulls. Gulls Larus hyperboreusand Herring Gulls L. ar- Condor 77~495-499. gentatusin Iceland. Ibis 112:340-362. RYDER,J. P. 1978. Possibleorigins and adaptive val- JEHL,J. R. 1971. A hybrid Glaucous x Herring gull ue of female-female pairing in gulls. Proc. Colonial from San Diego. Calif. Birds 2:27-32. Waterbird Group 2:534. LORENZ,K. 1970. Studies in animal and human be- RYDER,J. P., ANDP. L. SOMPPI. 1979. Female-female haviour, Vols. 1 & 2. Harvard Univ. Press, Cam- pairing in Ring-billed Gulls. Auk 96: l-5. bridge, MA. 401 & 366 pp. SOUTHERN,L. K., S. R. PATTON,AND W. E. SOUTHERN. LUDWIG, J. P. 1974. Recent changes in the Ring- 1982. Nocturnal predation on Larus gulls. Colonial billed Gull population and biology in the Laurentian Waterbirds 5: 169-l 72. Great Lakes. Auk 91:575-594. SOUTHERN,W. E. 1980. Comparative distribution MAYR, E. 1984. The contributions of ornithology to and orientation of North American gulls. Pp. 449- biology. BioSci. 34:250-254. 498 in J. Burger, B. L. Olla, and H. E. Winn (eds.). MILLER, D. E., AND J. T. EMLEN. 1975. Individual Behavior of marine animals, Vol. 4. Plenum Publ. chick recognition and family integrity in the Ring- Corp., NY. billed Gull. Behaviour 52: 122-144. SOUTHERN,W. E., S. R. PATTON,L. K. SOUTHERN,AND MILLS, J. A. 1973. The influence of age and pair- L. A. HANNERS. 1985. Effects of nine years of fox bond on the breedingbiology of the Red-billed Gull predation on two speciesof breedinggulls. Auk 102: Larus novaehollandiaescopulinus.J. Anim. Ecol. 42: 827-833. 147. SPEAR,L. B., D. G. AINLEY, AND R. P. HENDERSON. MONTEVECCHI,W. 1978. Nest site selection and its 1986. Postfledgling parental care in the Western survival value among Laughing Gulls. Behav. Ecol. Gull. Condor 88: 194-l 99. Sociobiol. 4: 143-l 6 1. TINBERGEN,N. 1953. The Herring Gull’s world. Col- MOORE,W. S. 1977. An evaluation of narrow hybrid lins, London. 255 pp. zones in vertebrates.Quart. Rev. Biol. 52~263-277. TUCKER,V. A. 1972. Metabolism during flight in the MOYNIHAN,M. 1958a. Notes on the behavior of some LaughingGull (Larus atricillu). Am. J. Physiol. 222: North American gulls: II. Non-aerial hostile behav- 237-245. ior of adults. Behaviour 12:95-l 82. VERMEER,K. 1963. The breedingecology of the Glau- MOYNIHAN,M. 1958b. Notes on the behavior of some cous-wingedGull (Lams gluuc&cens)on Mandarte North American gulls:III. Pairing behavior. Behav- Island, B.C. Occas. Papers B.C. Prov. Mus. 13:1- iour 13:112-130. 104. PATTON,S. R. 1986. Comparative foraging ecology WINKLER,D. W. 1985. Factors determining a clutch of three speciesof gulls (Lams) at urban landfills in size reduction in California Gulls (Lams culiforni- west-central Florida. Unpubl. Ph.D. dissertation, cw): a multi-hypothesisapproach. Evolution 39:667- Univ. South Florida, Tampa, FL. 677. ROBERT,H. C., AND C. J. RALPH. 1975. Effects of