**

Egg Island (**.*** N, -***.*** W) in western Lake

Athabasca (Figure 1) supports the largest Caspian Tern

(Hydroprogne caspia) colony in the province of Alber- ta (http://tpr.alberta.ca/parks/managing/sitedesc_can shield.asp). In recognition of this fact, the island was designated an ecological reserve by the province in 1992. It is the smallest (0.36 ha) such reserve in Alber- ta. Egg Island is approximately 70 m long by 40 m

wide, is elliptical in shape, and has a surface of pebble, cobble, and boulder gravel. It rises to a maximum

elevation of approximately 2.5 m above lake level. The island also supports breeding populations of Cal- ifornia Gulls (Larus californicus) and Herring Gulls

(Larus argentatus). Terns have likely nested in this area since at least the early 1900s. Sightings of Caspian Terns in the vicinity of Egg Island date back to 1903. Caspian Terns were observed in the Lake Athabasca

Delta in June 1903 (Preble 1908) and 1907 (Seton

1911). Soper (1942) made additional sightings in the Delta in late May and late June in 1932 and 1933,

respectively. The earliest census of Caspian Terns nesting on Egg Island was completed in 1952 with

approximately 20 breeding pairs reported (Salt and Wilk 1958, 1966; Salt and Salt 1976). Surveys were conducted intermittently in subsequent years. In early July 1971, Hohn (1973) visited Egg Island and esti- mated there were approximately 20 pairs of Caspian Terns and 50-80 pairs of California Gulls nesting on the island. Weseloh and Cocks (1979) censused the

island again in June, 1977 and counted 47 Caspian

Tern nests along with one Herring Gull nest. They esti- mated a maximum of 100 pairs of California Gulls

nesting on the island. Weseloh and Cocks (1979) pro- vide an excellent summary of the early Caspian Tern accounts for this region. In more recent years, Nord- strom and coworkers visited the island on two occa- sions. On 12 July 1990, Nordstrom (unpublished data) estimated approximately 150-200 adult Caspian Terns were breeding on the island. Data for other species were not collected. On 11 June 2001, Nordstrom, Vuj- novic and Thomas (unpublished data) reported at least 150 pairs of nesting Caspian Terns. They also estimat- ed that there were about 400 adult California Gulls, about 10 adult Herring Gulls, about 60 adult Ring- billed Gulls and about 30 adult Common Terns on/

around the island. However, there are no records of the latter two species nesting on the island.

Parts of northern Alberta have seen a significant in- crease in industrial activity over the past two decades. This is evident in the Fort McMurray area where the Oil Sands are under development (National Energy

Board 2004*, Alberta Environment 2008*). A major

river, the Athabasca River, flows through Fort McMur- ray and the area where many of the Oil Sands opera- tions are underway. The river flows northwards into western Lake Athabasca approximately 200 km down-

stream from Fort McMurray, the industrial hub of Oil Sands development (see Figure 1). The intention of our research was to provide updated information regard- ing the size of the populations of colonial waterbirds that breed on Egg Island. These data will be used to assess future trends in waterbird populations as a result of environmental change.

Methods

On 14 June 2009, we visited Egg Island via float-

plane (Figure 2). Snow and ice drifts were still present in waters adjacent to some parts of the island but, over- all, the waters of Lake Athabasca were ice-free. We arrived on the island at 08:00 (Mountain Standard

Time, UTC-7) and spent approximately 1 hour count- ing nests, taking egg measurements for California

Gulls, and collecting Caspian Tern and California Gull eggs for toxicological and dietary analysis. Here, we report population, clutch size distribution, and egg size data. Egg volume was estimated using the equation: Colonial Waterbirds Nesting on Egg Island, Lake Athabasca, 2009 CRAIG HEBERT1, WAYNE NORDSTROM2, and LAIRD SHUTT1

1Environment Canada, Wildlife and Landscape Science Directorate, National Wildlife Research Centre, 1125 Colonel By Drive, Ottawa, Ontario K1A 0H3 Canada

2Alberta Parks, Parks Ecology Program, 3rd floor, Oxbridge Place, 9820 – 106 Street, Edmonton, Alberta T5K 2J6 Canada Hebert, Craig, Wayne Nordstrom, and Laird Shutt. 2010. Colonial waterbirds nesting on Egg Island, Lake Athabasca, 2009. Canadian Field-Naturalist 124(1): 49–53.

In June 2009 a census was conducted of colonial waterbirds breeding on Egg Island in western Lake Athabasca. This island supports the largest breeding colony of Caspian Terns (Hydroprogne caspia) in Alberta. California Gulls (Larus californi- cus) and Herring Gulls (Larus argentatus) also nest on the island. One hundred and one Caspian Tern nests (=pairs) were counted during 2009. Since 1990, the number of terns nesting on the island appears stable. However, more frequent surveys of waterbird populations are recommended, particularly in light of growing industrial activity in this region. Key Words: Caspian Tern, Hydroprogne caspia, California Gull, Larus californicus, Herring Gull, Larus argentatus, Egg Island, Lake Athabasca, Alberta.

50 THE CANADIAN FIELD-NATURALIST Vol. 124

FIGURE 1. Map of the study region.

Volume (cm3) = 0.489 (length breadth2)/1000

(Ryder 1975)

Two biologists surveyed the entire island and count- ed nests for each of three species: Caspian Terns, California Gulls, and Herring Gulls. For California Gulls, egg measurements (length and breadth) were

obtained from completed 3-egg clutches. Similar data are not reported for the other two species because there were no 3-egg clutches for Caspian Terns and there were few Herring Gull nests.

Results

Caspian Terns were the most abundant species breed- ing on the island with 101 nests counted (Figure 3). In addition, there were 87 California Gull nests and 3 Herring Gull nests. Clutch size distribution data were also collected and are shown in Table 1. Average clutch size for Caspian Terns breeding in northern North

America is three eggs (Bent 1921). Similarly, modal 2010 HEBERT, NORDSTROM, AND SHUTT: COLONIAL WATERBIRDS NESTING 51 TABLE 1. Clutch size distribution data for waterbird species nesting on Egg Island, 14 June, 2009.

Species Clutch Size Total

0123

Caspian Tern 29 31 41 0 101

California Gull 14 29 22 22 87

Herring Gull 0012 3

FIGURE 2. Aerial view of Egg Island, Lake Athabasca, 14 June 2009. FIGURE 3. Approximately one-third of the Caspian Terns breeding on Egg Island, Lake Athabasca, 14 June 2009. clutch size for California Gulls nesting at another Alberta colony was three eggs (Vermeer 1970). Her- ring Gulls have also been reported to have a modal clutch size of three eggs (Tinbergen 1960). Clutch size distribution data indicated that egg-laying was still occurring for all species with the gulls somewhat more advanced than the terns. Mean ( standard deviation) egg size data from 3-egg clutches of California Gulls were as follows: length 64.59 2.33 mm, breadth

45.73 1.33 mm, volume 66.14 4.99 cm3. Mean

clutch volume was 198.43 11.00 cm3. Mean per-

cent difference between the largest and smallest egg within a clutch (intra-clutch variation in egg size) was 9.76 6.20%. With respect to the collection of fresh eggs, the timing of the visit on 14 June was nearly opti- mal as eggs from all species were available but there were no complete three-egg clutches for Caspian Terns. Future visits (assuming similar weather conditions) could be delayed for several days to ensure the pres- ence of complete clutches for all species.

Discussion

The nest count data reported here are consistent with census information from 1990 and 2001. Although the level of accuracy of the counts varied during the last three surveys, they indicated that the number of Caspi- an Terns breeding on the island reached its peak dur- ing the past two decades and has been stable at 100- 200 pairs. This trend combined with forthcoming

information regarding contaminant levels in the 2009 eggs will provide a benchmark against which to eval- uate future change. In light of growing economic

development in this region, more frequent censuses of waterbird populations on Egg Island are recommended. Waterbirds, such as terns and gulls, are useful indica- tors of environmental quality and ecosystem change

(Kushlan 1993; Hebert et al. 1999, 2008). Egg size data for California Gulls were similar to those report- ed previously for that species in Alberta (Vermeer 1969). However, mean clutch volumes and intra-clutch differences in egg size showed substantial variation among clutches. Such endpoints can be valuable in

assessing food stress and their long-term monitoring can provide insights into how ecosystem change may alter food availability for top predators (Hebert et al. 2002, 2009). Regular monitoring of waterbird popu- lations would be a useful addition to programs assess- ing the potential environmental impacts of Oil Sands development (e.g., Regional Aquatics Monitoring Pro- gram, see Golder Associates 2003*) and for assessing ecological change in general.

Acknowledgments

The authors thank Fish and Wildlife Division of

Alberta Sustainable Resource Development and Alber- ta Tourism, Parks, and Recreation for granting permits allowing this work to take place. Permits were also obtained from the Canadian Wildlife Service. Seth

Melmock of McMurray Aviation provided transporta-

tion to the island. Jeannine Paquette produced Figure 1. A. J. Erskine and C. Stuart Houston provided com- ments that improved the manuscript. Environment

Canada’s Ecotoxicology and Wildlife Health Program supported this research.

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RAMP Steering Committee. Calgary, Alberta.

National Energy Board. 2004. Canada’s Oil Sands: Oppor- tunities and Challenges to 2015. http://www.neb.gc.ca/clf- nsi/rnrgynfmtn/nrgyrprt/lsnd/lsnd-eng.html. Government of Canada, National Energy Board, Calgary, Alberta. Literature Cited

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Received 17 November 2009

Accepted 24 April 2010

2010 HEBERT, NORDSTROM, AND SHUTT: COLONIAL WATERBIRDS NESTING 53

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