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Demography and Populations
Measures Of Breeding Activity
Age At First Breeding; Intervals Between Breeding
Unknown. Observations (see Breeding: immature stage, above) suggest first breeding may be when ≥2 yr old; probably breeds annually thereafter, but no specific evidence.
Clutch
Usually 3 eggs (see Breeding: eggs, above).
Annual And Lifetime Reproductive Success
No information on lifetime reproductive success. Limited information available for breeding success at colonies (see Table 1). Reproductive success for particular location can be quite variable from year to year and often dependent on weather and water levels. Productivity at a colony for any particular year may vary from 0 to 1.9 eggs hatching/nest; 0 to 1.6 young fledged/nest; survival of young difficult to determine after young leave nest at age 4 d.
Number Of Broods Normally Reared Per Season
No direct information; probably 1 brood/season even though replacement of lost clutches frequent.
Proportion Of Total Females That Rear At Least One Brood To Nest-Leaving Or Independence
No information.
Life Span And Survivorship
No information on annual adult survival rate. Maximum reported longevity 12 yr by individual banded as chick in Santa Clara Co., CA, and recovered dead in Tulare Co., CA (based on 73 recoveries of 9,512 birds banded; Klimkiewicz and Futcher 1989).
Disease And Body Parasites
Diseases
No information.
Body Parasites
Limited information. In Colorado, 9 of 10 terns examined infected with fluke Diplostomum spathaceum (Trematoda; Davies et al. 1973). Lice (Mallophaga) recorded from this species include Actornithophilus funebre, Philopterus melanocephalus, and Saemundssonia parvigenetalis (Peters 1936, Malcomson 1960).
Causes Of Mortality
Exposure
Egg loss possibly due to wave action in floating nests and beach nests close to water level; egg loss sometimes high, especially during storms or after heavy rains cause water levels to rise (McNicholl 1971, Cuthbert and Louis 1993, Fraser 1994a) or during high tides (Storey 1987, Mossman 1989). Wave and high water effects usually gradual, but single storms or prolonged heavy rains can destroy considerable proportion of eggs and young present as well as affect nesting substrate and habitat (see McNicholl 1971, 1982; Storey 1987; Russell and Harris 1990).
Predation
See Behavior: predation, above. Intense predation may lead to colony abandonment (Harrison 1979, Fraser 1997). During one year of 2-yr Minnesota study, colony of 132 pairs “failed during mid-incubation (15 June) in 1992 due, possibly, to predation by a Great Horned Owl . . . ” (Fraser 1997: 88–89).
Competition With Other Species
No information. Possible competition for nest sites in mixed-spec-ies colonies.
Range
Initial Dispersal From Natal Site
No information.
Fidelity To Breeding Site And Winter Home Range
No information for marked individuals. Single pair nesting 7 yr on Plum I., MA, presumed to be same individuals (Petersen 1997). Marsh colonies shift rapidly with changes in habitat suitability through changes in water level or vegetative growth, but recolonize when areas become suitable again. In Louisiana, colony persistence averaged 4.2 yr (range 1–8) over 15 yr survey (Visser and Peterson 1994).
Dispersal From Breeding Sites
Little information. Chick banded at Green Bay, WI, found nesting in Minnesota 10 yr later (G. Fraser pers. comm.).
Home Range
No information.
Population Status
Numbers
Recent published estimates of breeding populations within specific geographic areas include the following: Canada, 2,133–4,216 pairs (Alvo and McNicholl 1996); Great Lakes, 3,025 pairs in 45 colonies (Scharf et al. 1993); U.S. Atlantic Coast, 5,766 pairs; U.S. Gulf Coast, 23,096 pairs; U.S. Pacific Coast, 8,095 individuals (Spendelow and Patton 1988); and Baja California, Mexico, 30–35 pairs (Howell and Webb 1995).
Trends
Breeding Bird Survey (BBS) data for 1966–1999 show no statistically significant, long-term change for this species in the U.S. (+1.1%/yr, p = 0.27, n = 114); no state or region with adequate sample size for meaningful statistical analysis (Sauer et al. 2000). These data, however, must be interpreted cautiously; BBS methods not well suited for censusing colonial waterbirds.
Population Regulation
Reproductive success often low due to weather effects or predation, but this species appears to be well adapted to balance predation risk against weather hazards by nesting on variety of substrates, by flexibility in colony size, and by rapid re-laying following nest loss. Longevity undoubtedly an important factor enabling individual replacement even with several nesting failures. Factors affecting survival over winter and between fledging and first breeding unknown.
Mcnicholl, Martin K., Peter E. Lowther and John A. Hall. 2001. Forster's Tern (Sterna forsteri), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/595
