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Recent Changes in the Ring-Billed Gull Population and Biology in the Laurentian Great Lakes

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Recent Changes in the Ring-Billed Gull Population and Biology in the Laurentian Great Lakes RECENT CHANGES IN THE RING-BILLED GULL POPULATION AND BIOLOGY IN THE LAURENTIAN GREAT LAKES JAMESP. LUDWIG SINC• World War II the Ring-billedGull (Larus delawarensis)popu- lation of the Laurentian Great Lakes has been characterizedby a massive increasein the number of nesting birds in all of the lakes. Published data on Ring-billed Gulls (Ludwig 1943) and Herring Gulls (Larus argentatus) (Paynter 1949; Hickey 1952; Ludwig 1962, 1966) were unable to indicate logical reasonsfor the enormousincreases recorded; neither did publishedlife tables suggestthat such increaseswere pos- sible in a Larus gull. Faced with the fact of an enormouslyincreased gull populationon the Great Lakes,it seemedclear that eitherparameters of populationdynamics were incorrectlyestimated, or the bandingdata on which the estimatedmortality rates were basedwere inaccurate. Sev- eral workers (Hickey 1952, Hickey et al. 1966, Ludwig and Tomoff 1966) suggestedthat band loss could account for the unacceptablere- sults. The incrediblyrapid increaseof this populationthat occurredbe- tween 1960 and 1965 simply could not fit even the most optimistically constructedmodel of populationgrowth for the speciesbased on field estimatesof fledgingrates and a reducedadult death rate (Ludwig 1966). Exploratory trapping data from 1965 showedthat some birds raised in colonies of Lakes Erie and Ontario were recruited into Lake Huron colonies.This suggestedthat Great Lakes Ring-billedGulls of breedingage may move from colonyto colonyand from lake to lake in some numbers. Ecologistshave long recognizedthat most animal populationstend to remain relatively stable, fluctuating about a mean number from year to year in undisturbed ecosystems.Beeton (1965, 1966) cited an ex- ample of disruption of the Great Lakes in the virtual disappearanceof the Hexageniasp. mayflies from Lake Erie and the appearanceof huge populationsof formerly rare tubificid worms, nematodes,and fingernail clams; theseeffects he attributed to pollution. Thus ecosystemdisrup- tion in the Great Lakes is characterizedby irruptionsof formerly rare or absentspecies as well as extinctionsor decimationsof formerlyabun- dant species. The recentexplosive spread of the sealamprey (Petromyzon marinus) and alewife (Alosa pseudoharengus)with the nearly simultaneousde- cline of the commerciallyvaluable fish speciesunderscores the fragile quality of these ecosystems(Miller 1956, Smith 1963). The species 575 The Auk 91: 575-594. July 1974 576 JAMES P. LVDWIG [Auk, Vol. 91 diversity in these communitieshas always been low, largely owing to the recencyof deglaciationand geologicalstructure that prevented in- vasionsof waterborneorganisms. Possibly a more complex freshwater system would have evolved if these ecosystemshad been permitted to develop naturally for enough time. The intrusion of European man into North America also increased the rate of introductions into these lakes. The formerly effective barriers to invasionby waterbornespecies were torn down, admitting Atlantic anadromousspecies. Others were introduceddirectly. These introductions,together with massivechanges in theselakes' watersheds,have decimatedmuch of the original fauna. Ever-increasing additions of industrial and municipal waste continue to disrupt the modernGreat Lakes and to changethe trophic structure on which Ring-billedGulls depend. Lakes in recently deglaciatedareas tend to follow similar paths in succeedingfrom the oligotrophiccondition to the filled-in bog. The oligotrophiclake with nutrient-poor watershedsbecomes eutrophic and highly productive through gradual accumulationof nutrients that pro- vide impetus to plant growth and the filling of lake basins. The Lauren- tian Great Lakes were deglaciated between 14,000 and 10,000 years ago, and attained modern water levels only about 2,000 to 2,500 years ago. When North America was discoveredby Europeanman each of the Great Lakes was in some stage of oligotrophy, developingno oxygen debts in summer,and supportinglarge populationsof fishes,particularly coregonids.Eutrophication has been greatly acceleratedby the growth of a huge technically oriented human population around the lakes, which has regarded running water as a vehicle for waste disposal. Beeton (1965, 1966) discussedthe related problems of acceleratedaging and pollution of the Great Lakes, noting that amongthem only Lake Superior has not had significant rises in nutrients and dissolved solids in the last half century. Harlow (1966) found that the human population surroundingthe western Lake Erie basin contributed more than half of the nutrientsto that grosslypolluted and highly productiveecosystem. Most of the nutrient contributionwas in the form of sewage. At the apex of food chains associatedwith these lakes are Ring-billed Gulls and other secondarypredators. Adult Ring-bills are presenton the Great Lakes during most of the year. METHODS AND STUDY AREAS Because banders have visited the Ring-billed Gull colonies in the Thunder Bay region of northwesternLake Huron annually since 1932, coloniesthere were chosenfor study trapping sites from 1965 through 19(57. Ring-bill coloniesin the Beaver Islands of Northern Lake Michi- gan were visitedin 1965 in conjunctionwith a pesticidestudy of Herring July 1974] Ring-billed Gulls 577 Gulls (Ludwig and Tomoff 1966), and were visitedagain in 1966 and 1967. The Charity Islands Reef colonyin SaginawBay of Lake Huron was added in 1966 in conjunctionwith a study of the distribution of type E botulismin Ring-billed Gulls (Ludwig and Bromley 1967). Be- causedata from theseLake Huron-Lake Michigan coloniesproved that some birds were recruited from coloniesof Lake Erie, Lake Ontario, and the St. LawrenceRiver, the 1967 researchstrategy included trapping in those areas to estimate the amount of exchange of gulls between coloniesand lakes and to study colony social organization.The Mohawk Island colonyin easternLake Erie near Port Maitland, Ontario, and two coloniesin Lake Ontario (Little Gallo Island near HendersonHarbor, New York, and the Bluffs colony near Brighton, Ontario, within Presqu'ile ProvincialPark) were addedto the researchdesign in 1967. The Chantry Island colony near Southampton,Ontario, in eastern Lake Huron be- tween the Lake Huron and Lake Ontario colonies,was also included in 1967. Adult gulls were trapped in each of thesecolonies in 1967. Large numbers of adult birds banded as chicks had to be captured to obtain an adequatesample of birds of knownage and origin. I used a a•-inch mesh cannon net, Dill cannons,and electrically fired 110- grain blackpowder cartridges for catchingthe gullson their nests(Figure 1). Adult birds are most easily trapped in colonieswhen incubating or before the chicksare old enoughto run. Inevitably someeggs and nests are destroyedduring these operations,but clutchesdestroyed in the nestingseason by carelessstepping or falling projectilesare usually replaced.Adult birds are surprisinglylittle disturbedby cannonnetting in their coloniesearly in the season.Unlike Southern (1967b), I found little evidencethat cannonnetting causedbirds to abandontheir colonies. Seabirds are particularly mobile creatures. In the Great Lakes at leastthree species of terns,the Common(Sterna hirundo), Black (Chili- doniasniger), and Caspian(Hydroprogne caspia) have establishedre- producingpopulations. Herring, Ring-billed,and Great Black-backed Gulls (Larus marinus) are also established.The Little Gull (Larus minutus)is establishingitself in Lake Ontarionear Torontoand in Lake St. Clair. Great Black-backed Gulls nest at scattered locations in Lake Ontario and seempoised at the edge of the Great Lakes for an in- vasion. Bent (1921) recordedHerring Gulls, CommonTerns, Black Terns, and CaspianTerns breedingon islandsin the Great Lakes well back into the 19th century. Bent (1921) thought,as did Barrows(1912), that the Ring-billed Gull disappearedas a breedingspecies from GreatLakes islands early in the 20th century. Whetheror not it disappearedcompletely is not certain. If it was establishedbetween 1906 and 1925 it must have bred in small numbersin remoteparts of Lake Huron (GeorgianBay). Lud- 578 JAMES P. LuDwxo [Auk, Vol. 91 / Figure 1. A cannon-netted sample of Ring-billed Gulls, Chantry Island, 19 May 1967. wig (1943) recordedthe species'return to prominencein northern Lake Michigan and Lake Huron after 1926. By 1941 at least 26 islandshad supportedcolonies at least once dur- ing the previous 15 years. Several islands, including Scarecrow,St. Martin's Shoal, Halfmoon, and South Limestonein Lake Huron, appar- ently have supported colonies continuouslysince 1932 (see Ludwig 1962 for list of coloniesand their locations). By 1940 coloniesin Lakes Huron and Michigan supported a population approximating20,000 breedingpairs, and this portion of the Great Lakes populationapparently remainednearly stableat this level until about 1960 (Ludwig 1966). The reasonsfor this moderatereinvasion of the Great Lakes are obscuredby the past and by a lack of study; furthermorethe reasonsfor population stability between 1940 and 1960 are not apparent. Some shifting of gulls betweenislands during this period in Lakes Huron and Michigan took place, but no irruption of gulls occurredcomparable to the in- credible increase that came between 1960 and 1967. In 1960 the Ring-billed Gull populationof Lakes Huron and Michigan was estimatedto be 27,000 nestingpairs (Ludwig 1962). By 1967 this July 1974] Ring-billed Gulls 579 TABLE 1 ESTIMATES OF NESTI•O PAIRS I3I RING-BILLED GULL COLONIES OF LAKES HIIROl• AND MICIIIGAN 1960-67
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