Conservation and Management

Shooting And Trapping

Shooting, trapping, and collecting have been significant mortality factors in several populations. Lock (1993) reported that great numbers of adult terns were shot and trapped in Atlantic Canada and U.S. in last quarter of nineteenth century for millinery trade.

Pesticides And Other Contaminants/Toxics

Effects of contaminants on fish-eating birds have been well studied in Great Lakes, and impacts have been identified in some Caspian Tern colonies. By 1980–1981, residue levels of DDE, PCBs, and mirex in eggs of Great Lakes Caspian Terns were low and did not appear to have serious effect on reproduction, eggshell thickness, or population size and growth (Struger and Weseloh 1985). In 1990, concentrations of DDE found in plasma of Great Lakes Caspian Terns were less than threshold concentrations known to cause eggshell-thinning (average 0.107–0.281g/g wet weight, n = 123). However, concentrations of PCBs in plasma were greater than those of any other compound, and highest in birds from colonies in Green Bay, Lake Michigan (average 3.236–3.499 g/g wet weight, n = 10) and Saginaw Bay, Lake Huron (average 2.512 g/g wet weight, n = 15) both industrialized areas, and the most contaminated of Great Lakes’ breeding sites. When the proportion of Great Lakes adults banded as chicks in their natal area (n = 29) was correlated with mean PCB concentrations for each of 5 regions, a statistically significant negative correlation (r ²= 0.83, p < 0.001) was observed between mean con-centrations of PCBs by region and natal fidelity. Mora et al. (1993) postulated that reduced natal site fidelity at the colonies most contaminated with PCBs may be due to: increased mortality of young; accumulation of PCBs in postfledging individuals to concentrations which could cause increased mortality during migration due to utilization of fat reserves; and postfledging terns may have greater susceptibility to PCBs and other PHHs, which may result in greater mortality.

Grasman et al. (1996) found organochlorine-associated suppression of T-cell mediated immunity in prefledgling Caspian Tern chicks from the Great Lakes (total of 5 sites sampled, n = 35–50 chicks from each site); suppression was most severe at the more contaminated colonies in Saginaw Bay and Lake Ontario. PCBs were the contaminant most closely associated with immunosuppression. They concluded that contaminant-associated immunosuppresion provides a potential mechanism to explain low recruitment into the breeding population of Caspian Terns raised at highly contaminated colonies.

Eggs from Green Bay, Lake Michigan, and Saginaw Bay, Lake Huron, also had the highest PCB concentrations of eggs studied throughout Great Lakes (Ewins et al. 1994). High PCB concentrations may result in lowered reproductive success. In 1986, a major 100-yr flood occurred in Saginaw Bay/River ecosystem, which moved contaminated sediments and sediment-stored PCBs into the water column. Of 24 dead eggs examined here in 1987, Ludwig et al. (1993) reported half held abnormal embryos; they attributed major chick mortality at this site to inability to gain weight normally.

Collisions With Stationary/Moving Structures Or Objects

Reported to fly into electric wires (Cooke 1937), and to collide with vehicles, trains, and other objects (Tomkins 1934, Ludwig 1965).

Degradation Of Habitat

Not an important problem for Caspian Terns in North America; no data on win-tering sites.

Disturbance At Nest Sites; Direct Human/Research Impacts

Sensitive to human disturbance, especially early in breeding cycle and incubation period. During early stages of breeding, before eggs are laid, sudden deserting flights of entire colonies in response to human disturbances are typical. In colonies in ne. Lake Michigan, 22% of reproductive failures were caused by investigator disturbance that led to nest desertion (Cuthbert 1981). At 1 colony, cannon-netting activity in early Jun was the single greatest cause of reproductive failure, resulting in desertion by 445 pairs, about two-thirds of the colony. Many of these birds had been incubating <2 wk and had not developed strong nest-site attachment (Shugart et al. 1978).

Human disturbance at colonies facilitates egg predation by gulls when more wary terns are flushed from nests (Penland 1982, Quinn 1984). Egg mortality also results from actions of parent birds when they are upset by human intruders and knock eggs out of their nests when flushed quickly (FJC).

Chick mortality can greatly increase when humans enter colonies. In Grays Harbor, WA, researcher activities in a single day in 1 colony resulted in 30% of known chick mortality during a 16-d span (Penland 1982). Banding activities during 1 h in this colony caused estimated 35% mortality among chicks 6–10 d of age (Penland 1981). Investigator disturbance also precipitated early abandonment of nesting area and caused chick mortalities in a colony studied on Lake Ontario (Fetterolf and Blokpoel 1983). Rate of chick mortality from human disturbance increases as colony size increases as result of greater number of aggressive adults, defended territories, and time required for adults to relocate chicks after a disturbance (Penland 1976).

In addition to disrupting nesting activities, humans have severely impacted colonies by collecting eggs and adults for food (Bent 1921, Cott 1953, Ludwig 1965, Nettleship and Lock 1973), and through acts of vandalism (Penland 1976, Koonz 1982).

Conservation Status

Despite increasing numbers in the Great Lakes, Caspian Tern has special status in several areas. Canadian population was recognized as Rare in 1987 by the Committee on Status of Endangered Wildlife in Canada (COSEWIC; Blokpoel and Scharf 1991), and classified as “Vulnerable” in 1990 (Sirois et al. 1991). Because of small number of breeding sites in Ontario, the Ontario Ministry of Natural Resources (OMNR) identified this species as “Rare” in 1988 (Blokpoel and Scharf 1991); in 1994, Caspian Tern bred at only 13 sites (Neuman and Blokpoel 1997). Currently listed as Threatened in Michigan, Endangered in Wisconsin, and Species of Special Concern in Utah, Wyoming, Virginia, and Louisiana because of limited nest sites and declining numbers due to fluctuating water levels, predation, and or human disturbance. In Florida, species designated by the Florida Committee on Rare and Endangered Plants and Animals (FCREPA) as “Species of Special Concern” due to small numbers of breeding birds and breeding sites; will likely become official designation when state reviews species status (J. Rodgers Jr. pers. comm.). In Quebec, currently on official legal list of all species considered for “Threatened” or “Vulnerable” designation (M. Robert pers. comm.).

Measures Proposed And Taken

Conservation efforts usually aimed at nesting areas; focus is on colony protection or enhancement. Measures include providing artificial nest sites (Lampman et al. 1996), creating/maintaining islands from dredge or other materials (Parnell and Shields 1990, Clay 1992, Quinn et al. 1996), providing preferred or amending substrates, preventing or removing gull nests (Stadtlander et al. 1993, Quinn et al. 1996), covering nests to reduce egg predation by gulls (Quinn 1984), maintaining or suppressing vegetation (Clay 1992, Quinn et al. 1996), using decoys and taped vocalizations to attract terns (Lampman et al. 1996), and constructing tunnel systems to allow investigators access to blinds without disturbing nesting birds (G. Shugart pers. comm.). Other measures include limiting or preventing public access to breeding colonies, minimizing and carefully planning investigator activities (Penland 1976, Blokpoel 1981), preventing low-level overflights by aircraft during breeding season, monitoring populations to determine trends and shifts, and assessing effects of gull species in certain areas (Blokpoel and Harfenist 1986, D. Roby pers. comm.). Large colonies with good potential for long-term conservation should be protected from human development, such as runways, harbors, and buildings (Blokpoel and Scharf 1991).

Effectiveness Of Measures

Highest reproductive success occurs at remote colony sites free from human and predator disturbance. Actions by federal, state, or private landowners to create these conditions will contribute to conservation of species. Developing such conditions often means limiting human access. At sites where habitat is lost or otherwise unsuitable, artificial islands and nest sites have been successful. At Hamilton Harbour, Lake Ontario, 3 islands were constructed during winter 1995–1996 to increase biodiversity of colonial nesters. After substrate preferences were determined experimentally, the area designated for Caspian Terns was surfaced with sand and pea-gravel for lining of nest rims (see Breeding: nest site, above). The colony was established, and 200–300 clutches were initiated in subsequent years (Quinn and Sirdevan in press). In addition, a raft was installed in 1993 and used successfully by at least 50 pairs in 1995, indicating that this species will breed in significant numbers on artificial floating platforms (Lampman et al. 1996). When investigators are present in colony, nest covers significantly reduce egg predation by gulls and should be employed when researchers are working in small colonies (75–100 nests). Nest covers may be less effective in larger colonies because predation may occur at unprotected nests outside of study area (Quinn 1984).