POPULATION DYNAMICS

Recent increases in Double-crested Cormorants in the United States Great Lakes

William C. Scharf and Gary W. Shugart

HERECENT HISTORICAL rise(1910- 1945) and fall (1946-1975) of Great Lakes populations of the Double- crested Cormorant (Phalacrocorax auntus) has been well documented by Postupalsky (1978), and in reports of recent increases in Canadian waters of by Blokpoel et al. (1980). Further increases in the Canadian wa- ters of , during 1980, have been reported by D. V. Weseloh (pers. comm.). In this paper we report on the magnitudeof increasesin United States Great Lakes waters from 1977 to 1980. The United States Great Lakes popu- lation of cormorants in 1977 was 157 in three colonies, a 26% increase over 1976 (Scharf et al. 1978 and 1979). In conjunction with a Common Tern (Sterna hirundo) survey of the Michi- Fig. 1 gan Great Lakes shoreline in 1980 and w•th the cooperation of other ob- shelves on isolated islands. The tree- nesting birds, and one, Scarecrow Is- servers, we were able to document a nestersutilize trees varying from decid- land in Lake Huron, has only tree- 454% increase in this species since uouselms (Ulmus spp.) and oaks(Quer- nesters that are utilizing former Great 1977. The survey was conducted by cus spp.) to coniferous cedars (Thuja Blue Heron (Ardea herodias) nests actual nest counts and in some in- spp.). One site, Cat and Willow islands All of the island habitats are shared stancesby counting nests on aerial pho- in Lake 's Green Bay, has 185 by Herring Gulls (Larus argentatus), tographs. We counted a total of 714 artificial nesting platforms built on util- that will prey upon eggs and small nests at 12 colonies on four United ity poles erected in the bay by Wiscon- chicks of cormorants whenever the States Great Lakes (Table 1, Fig. 1). sin Public Service Corporation for the adult cormorants are kept off their Nuclei of reproductive successcon- cormorants (Green Bay Press Gazette, nests. Hence, caution is suggestedfor tnbuting to the recolonization process May 17, 1980). At least two of the new census takers, banders and other •n- seemto be in three areas: a) at the Green colonies have both tree- and ground- trudinghumans. In somecolonies Ring- Bay area of northwestern Lake Michi- ganwhere two new colonieswere noted Table 1. Cormorant nestingsites in United States Great Lakes, 1980. m 1976 and 1977; b) the Little Galloo Site Lake Census Method Nests Island colony of eastern Lake Ontario where colony growth has been over I.• Gull Island Superior Ground Count--Kjos 53 2. TaquamenonIsland Superior Ground Count 34 200% since 1977;and c) the Lake Supe- 3. Cat-Willow Island Michigan G. B. Press Gazette 100 rior and western influx postulated by 4. Gravelly Island Michigan Ground Count 91 Blokpoel et al. (1980). These divergent 5. Little Gull Island Michigan Ground Count 16 hypothetical sources underscore the 6. Fish Island Michigan Aerial Photog. 70 7. Gravel Island Michigan Aerial Photog. 25 w•despread nature of the population 8. Spider Island Michigan Aerial Photog. 45 increaseof this speciesand the proba- 9. Gull Island Michi an Ground Count 8 bfi•ty of there being several sourcesof 10. Scarecrow Island Huron Aerial Count 12 b•rds for recolonization. 11. Black River Island Huron Ground Count 2 Favored habitats for ground-nesting 12. Little Galloo Island Ontario Ground Count--Weseloh 276 cormorants are cobble beaches or rock •Numbersare keyed to Figure 1.

910 American B•rds, November 1981 balled Gulls (Larus delawarensts), RARE OCCURRENCE Black-crowned Night Herons (Nycti- corax nycticorax) , and Cattle Egrets (Bubulcusibis) nest in addition to the Herring Gulls and Great Blue Herons. At the colony at Gravelly Island, Lake A North American record of the Asiatic M•chigan, almost-fledged young were Marbled Murrelet countedas an indicationof productivity per nest July 12, 1980. There were 125 (Brachyramphus marmoratus perdix) chicks and 87 nests, for an average of I 43 per nest. On the same day at the Daniel R. Jehl and Joseph R. Jehl, Jr. same location there were four recent nests with 1-2 eggs each. The latest nesting cormorants were those on Gull NAUGUST 9, 1981, at Mono Lake, dov, 1951: 245-47). The closest nesting Island, . There were two Mono County, California, DRJ locality is approximately 6000 km from nestsand six chicksthere on August 23, found a Marbled Murrelet (Brachyram- Mono Lake. 1980. Similar late nestingswere seen in phus marmoratus) in breedingplumage There are no publishedrecords of the 1976at Fish Island, Lake Michigan, the washed ashore on a beach that had been Asiatic Marbled Murrelet in North first year the cormorants nested there. censused regularly all summer, most America. Apparently the only premous recently on August 6. JRJ, who pre- inland report for a Marbled Murrelet ACKNOWLEDGMENTS paredthe specimenas a study skin, (San anywhere in North America away from Diego Natural History Museum no. the immediateproximity of the breeding ETHANK THE Michigan Depart- 41544;Fig. 1)estimated that it hadbeen grounds of B. m. marmoratus (which ment of Natural Resources and deadfor 11/2days. The bird was an adult may be as much as 40 km inland along the United States Fish and Wildlife male, testes 10 x 3 ram; it was emaci- the west coast) is from Quebec, where Service who funded our transportation ated, lacking subcutaneousfat, and its one was shot by a hunter in November to these locations under grants to study stomach was empty. 1979(David and Gosselin, 1980). Fortu- Common Terns and colonial nesting In the field we recognized the murre- nately, that report included a photo- b•rds. Also, Chuck Kjos and D. V. let as being unusually large. S. I. Bond graphwith a ruled scale, which showed Weseloh provided counts we were un- and G. McCaskie compared it with ref- that the Quebec specimen was also able to make and Donald DeRuiter pi- erence matedhalin the San Diego Natu- large and possesseda white-eye ring loted the floatplaneto the islands. ral History Museum and, on the basisof Our suspicion that it represented an a description by Ridgway (1919), unrecognized example of perdix was LITERATURE CITED identified it as the asiatic race B.m. confirmed by S. G. Sealy, who had perdix. The identification was anticipatedour findingsand had already BLOKPOEL, H., J.P. RYDER, I. SED- confirmed by Spencer G. Sealy. examined the specimenin conjunction DON, and W. R. CARSWELL. 1980. with his studies of the distribution and Colonial waterbirds nesting in Canadian Formerly recognized as a distinct Lake Superior. Progress Notes Canad. species (Brachyramphus perdix) the morphologyof Brachyramphus murre- Wild. Serv. No. 118:1-13. Asiatic Marbled Murrelet has a distinct lets. POSTUPALSKY, S. 1978. Toxic chemicals white eye-dhng,lacks rufous tones on and cormorant populations in the Great Lakes. Can. Wildl. Serv. Wild. Toxical. the upper parts in breeding plumage Div. Manuscr. Rep. No. 40. Ottawa. 25 (Ridgway 1919), and is larger than the LCIDSARE EXTREMELY rare inland PP. North American race (B.m. marmora- and only two species, Dovek•e SCHARF, W. C., G. W. SHUGART, M. L. tus). (Alle alle) and Ancient Murrelet (Syn- CHAMBERLIN. 1978. Colonial birds Dimensionsof the Mono Lake speci- thliboramphus antiquus) occur there nestingon man-madeand natural sitesin the U.S. Great Lakes. Rep. WES-TR-D- men are: wing (flat) 146 ram; exposed with appreciablefrequency. Almost all 78-10. U.S. Army Eng. Waterw. Exp. culmen 22.3 ram; tarsus, 17.9 ram, recordsseem to be associatedwith per- Stn. Vicksburg, Miss. 140 pp. weight 204 g (emaciated). Dimensions iods of severe coastal storm and poor SCHARF, W. C. 1979. Nesting and migra- of breeding male B.m. marmoratus visibility that occur during the late fall tion areas of birds of the U.S. Great and early spring migration periods Lakes (30 April to 25 August 1976). U.S. from British Columbia (Sealy 1975)are: Fish Wildl. Serv. Off. Biol. Serv. FWS/ wing (flat) 128-140 (134.2) ram, N =25; (Munyer 1965, Verbeek 1966; Murphy OBS-77/2. 113 pp. exposed culmen 13.2-17.4 (15.5) ram, and Vogt, 1933). While that explanation N=38; tarsus 15.1-17.6 (16.2) ram, may be relevant to the appearance of --Division of Science and N=37; weight 196.2-232.2 (218.5) g, perdix in Quebec in November, it seems Mathematics, N= 10. unlikely to apply to the Mono Lake Northwestern Michigan College, Although the nest of the Asiatic Mar- specimen, which appeared in late sum- Traverse City, MI 49684. bled Murrelet was discovered prior to mer following a calm and storm-free (ScharJ);Ecology Program, Rutgers that of the American form, the Asiatic period that had persisted for the pre- University, New Brunswick, NY 08903 bird is less well known. Its breeding vious month in northern California. (ShugarO. range seems to be concentrated along We are grateful to Suzanne I. Bond, the east coast of the Kamchatka Penin- Guy McCaskie, and Spencer G. Sealy sula and on the mainland coast of the for their help in preparation of th•s Sea of Okhotsk (Dement'ev and Gla- report.

Volume 35, Number 6 911