Species: Chlidonias niger

Most terns in the northeastern United States and Canada return to breeding areas during the first two weeks of May, although birds may arrive in western New York as early as the last week of April (Laughlin and Kibbe 1985, Firstencel 1987, Gerson 1987). Conspicuous aerial courtship displays characterize the courtship period, which begins soon after arrival at the breeding site. In the "high-flight", a group of 2-20 terns ascend together to a great height then split into smaller groups of two or three and descend in rapid glides (Baggerman et al. 1956). During the "fish-flight", a male tern carries a small fish or large insect in its bill and is closely followed by a female as the two fly about the marsh. At the close of this aerial display the male follows the female to a perch and feeds her (Baggerman et al. 1956). <br><br>In the northeastern United States egg laying begins in late May, but may be initiated as late as the middle of July. Nests with eggs were observed at one site in western New York from 24 May to 12 July (Firstencel 1987). During a 1989 survey of colony sites throughout New York, nests with eggs were observed as early as 25 May and as late as 18 July (Novak 1990). Not known to be double brooded and late nests probably represent renesting attempts. At Rush Lake in Wisconsin, Bailey (1977) observed a trend toward three nesting peaks, one in late May, one in early to mid June, and one in late July. This pattern was attributed to two initial nesting periods characterized by a high degree of synchrony, followed by a period of renesting (Bailey 1977). Baggerman et al. (1956) also reported highly synchronous nesting activity. <br><br>One to five eggs may be laid, although the normal clutch is usually two or three (Bent 1921). Clutches with four eggs have been reported in only two recent studies (Bergman et al. 1970, Mossman 1980) and are apparently quite rare. Other than Bent (1921), there are no published reports of five egg clutches. Single egg clutches may often be replacement nests or nests where one or more eggs have already been lost (Bent 1921, Cuthbert 1954, Firstencel 1987). In a recent study in Wisconsin, the average clutch size for 41 closely monitored nests was 2.9 (Bailey 1977). Four nests had clutches of two, but no nests contained less than two or more than three eggs. Average clutch sizes reported in other recent studies where nests may not have been monitored as carefully, range from 2.25 to 2.75 (Cuthbert 1954, Goodwin 1960, Bergman et al. 1970, Mossman 1981, Firstencel 1987, Novak 1990). Incubation begins with the laying of the first egg, and eggs require 20-24 days to hatch (Goodwin 1960, Bergman et al. 1970, Bailey 1977). Both sexes incubate (Goodwin 1960). <br><br>Young are tended by both parents. Chicks are able to swim, walk and run by the time they are two days old (Goodwin 1960). The chicks grow rapidly, doubling their weight in less than three days and quadrupling their weight in less than six days (Bailey 1977). The rate of weight gain slows after the eighth day. In some cases, chicks may be relocated from the nest site to "auxiliary" nests within a few days after hatching (Cuthbert 1954, Firstencel 1987). If disturbance at the nest is minimal, young may remain at the original nest site for as long as 14-25 days, although they hide in the vegetation at the sign of danger and may be found swimming as far as 40 ft from the nest (Cuthbert 1954, Goodwin 1960). The age at fledging is difficult to determine. Bailey (1977) reported fledging at 18 and 19 days for two chicks of known age and suggested that the majority of chicks are flying at 21 days of age with a mean fledging age possibly less than 20 days. Baggerman et al. (1956) and Goodwin (1960) reported fledging at 21 days. Young are fully fledged at about four weeks. <br><br>Estimates of nest success (expressed as a percentage of nests where at least one egg was hatched successfully) from four nest studies are as follows: 27% (15 of 55 nests) in Ontario, 29% (56 of 192 nests) in Iowa, 34% (13 of 38 nests) in Wisconsin, and 50% (12 of 24 nests) in New York (Dunn 1979, Bergman et al. 1970, Bailey 1977, Firstencel 1987, respectively). There was no obvious correlation between nest success, height of eggs above water, and number of nests per substrate in the Iowa study (Bergman et al. 1970). <br><br>Survival of young to fledging is difficult to measure because of the mobility of chicks. Bailey (1977) attempted to measure chick survival by placing fencing around nests to prevent young from moving away from the nest site. Just three of 26 (12%) chicks monitored fledged successfully. Sixteen chicks were lost to predation and several chicks died in the pen netting. Fledging success at unfenced nests (perhaps a better representation of fledging success) was estimated at 15-20% (Bailey 1977). Recent surveys have presented estimates of reproductive success based on the number of fledglings produced per egg laid in the colony (Rabenold 1987, Novak 1990). Estimates for three small (less than 10 pairs) colonies in Indiana were 0%, 53%, and 67%, for an overall average of 30% (Rabenold 1987). Estimates also varied widely for 19 sites in New York, from 4% to 38%, with an overall average of 20% (Novak 1990). Mossman (1980) reported a 25% reproductive success based on the ratio of young: adults observed at one study area in Wisconsin. <br><br>The similarity between reproductive or fledging success rates and nest success (hatching success) supports the observation by Dunn (1979) that most losses occur during the egg stage. Wind and wave action, and storms were responsible for most nest losses in several studies (Bergman et al. 1970, Bailey 1977, Dunn 1979, Faber and Nosek 1985, Chapman-Mosher 1987). Nest losses have also been attributed to egg inviability, predation, muskrat activity, and intraspecific interactions (Bergman et al. 1970, Bailey 1977, Dunn 1979, Firstencel 1987). <br><br>Has been described as a semi-colonial nesting species (Cuthbert 1954, Bergman et al. 1970). Nests may be clumped closely in favorable habitat or more widely scattered in other, perhaps less favorable areas. As is typical of colonial nesting gulls and terns, terns will join together to defend the nesting area from intruders (Cuthbert 1954).