Common Tern Sterna Hirundo
Within Ohio, breeding Common Terns have always been Townsend 1985). Contamination by pesticides and other toxic restricted to the Western Basin of Lake Erie in Lucas, Ottawa, chemicals may also reduce the success of nesting terns. and Erie counties. Throughout most of the 20th century, adult Along western Lake Erie, the preferred nesting sites of terns were regularly observed as they gracefully foraged for small Common Terns are natural or man–made islands that are free fish over the open waters of the lake. In recent years, however, of mammalian predators and human disturbance. These Common Terns have fallen on hard times and the small remnant colonies may be shared with other terns and gulls. They will population is in danger of disappearing from the state. also utilize mainland beaches and dredge disposal areas, but This is not the first time Common Terns have been faced with only when islands are unavailable. Their nests are placed on extirpation from Ohio. In the 19th century, they were virtually the ground on sandy or gravelly substrates. The island sites are eliminated by the millinery trade, but quickly recovered after they either barren or sparsely vegetated, while the mainland received protection. In the early 1900s, these terns were once colonies tend to be more densely vegetated (Peck and James again quite numerous along western Lake Erie with an estimated 1983). When their populations were larger, a few isolated population of 3,000 pairs (Jones 1903). pairs also nested within marshes where they placed their Their population trends during the 20th century were de- nests on muskrat houses (Campbell 1940). scribed by Peterjohn (1989a) and are only briefly summarized here. Despite frequent shifts in the locations of their large nesting colonies, Common Terns remained numerous along western Lake Erie through the 1940s with estimates of 2,000–5,000 pairs. In the 1950s, they were forced to abandon a number of their former breeding sites, but a single large colony usually formed some- where along western Lake Erie each year. This colony was normally composed of 1,000–2,000 pairs, but totalled 5,000 in 1967. The last colony of 1,000+ pairs was reported in 1970. High lake levels eliminated the Ohio nesting colonies between 1971 and 1974, but 350 pairs formed a new colony at Oregon (Lucas County) in 1975. Their declining fortunes along western Lake Erie were symptomatic of significant decreases in nesting Common Tern populations throughout the Great Lakes region (Courtney and Blokpoel 1983, Shugart and Scharf 1983). At the beginning of the Atlas Project, breeding Common Terns were restricted to the Oregon colony. In 1982, this colony was reduced to fewer than 100 pairs, none of which successfully raised young. The site was abandoned in 1983. In 1985, at least 10 pairs of terns attempted to nest at a small island near the mouth of Sandusky Bay in Erie County. They did not return to this site in 1986, but three pairs nested at Oregon. The only Alvin E. Staffan nesting record in 1987 was provided by two unsuccessful pairs at Ottawa National Wildlife Refuge (Lucas County). During 1988– 1989, as many as 47 pairs have been counted in a diked marsh Common Terns normally return to their Ohio colonies during near the Cedar Point Causeway in Erie County, although few the last days of April and first half of May. Nests with eggs have young have been raised. The Ottawa Wildlife Refuge site hosted been reported as early as May 7 (Shields and Townsend 1985), only a few unsuccessful breeding pairs in 1989. but most first clutches are laid between May 15 and June 5. In addition to the Ohio colonies, Common Terns also nest in Recently hatched young have been noted by June 5 (Campbell the Ontario and Michigan portions of western Lake Erie (Cadman 1968), but most young do not hatch until mid–June. These et al. 1987, Payne 1983). While there is interchange of nesting young terns normally leave the colony during the second half of terns between these colonies, their reduction within Ohio is not July. Common Terns frequently renest if their first clutches are compensated for by increases in other colonies. In fact, their destroyed. Renesting attempts are responsible for incubating numbers have noticeably declined in every colony since the adults through August 4 (Campbell 1968). These late nests have 1960s. A number of factors have contributed to this decline. produced recently hatched young during July, but few of these Expanding gull populations usurped many of the former tern young survive to fledge in late August. nesting sites and forced terns to utilize less than optimal locations where they are subjected to increased predation. Hence, reproduc- tive success at their few remaining colonies is very poor and insufficient to maintain their small populations (Shields and
124 Blocks Special Areas Other Observations Confirmed Probable Possible
Analysis of Block Data by Physiographic Region Summary of Total Blocks % Regional Ave. # Individ Breeding Status Physiographic Blocks with with % per BBS Route No. of Blocks in Which Region Surveyed Data Data for Ohio (1982–1987) Species Recorded Lake Plain 95 1 1.1 100.0 – Till Plain 271 – – – – Total 1 0.1% Ill. Till Plain 46 – – – – Confirmed 1 100.0% Glaciated Plateau 140 – – – – Probable – – Unglaciated Plateau 212 – – – – Possible – –
125 Common Tern