New York Natural Heritage Program
Caspian Tern
Hydroprogne caspia (Pallas, 1770)
Birds

Threats [-]
Caspian Terns are sensitive to human disturbance at nest sites especially in the early stages of nesting and incubation (Cuthbert and Wires 1999) and nearby. Well meaning researchers, recreational boaters, and fishermen may, therefore, pose a threat to new or unprotected colonies. Entire colonies have abandoned nesting areas in response to human presence (Cuthbert 1981). Investigator effects occur during research when observers flush birds from the nest inadvertently enabling predators such as gulls access to the nest while the parents are agitated by the intruder. Adults may even abandon chicks due to the presence of researchers, for instance during banding efforts (Penland 1981, Penland 1982). Fetterolf and Blokpoel (1983) used a combination of remote monitoring of tern nesting sites and refrained from visiting nesting areas during the post-hatching period to limit investigator effects on a colony near Toronto on Lake Ontario. They cite this method as a necessity to accurately document fledgling success and concluded that nesting success was greatly increased in years where this method was employed in lieu of more frequent visits (Fetterolf and Blokpoel 1983). The Great Lakes population inhabits remote natural islands and a few sites on the mainland shores of the lakes (Wires and Cuthbert 2000). Since this species is sensitive to human disturbance, development of these or surrounding sites would threaten populations; although both nesting colonies in New York are located on protected islands. Also North American populations have congregated in high densities at a smaller number of nesting sites (Wires and Cuthbert 2000), making the species more vulnerable to stochastic events including disease, weather, and changing environmental conditions. In New York, there are only two known nesting colonies. In 2006, 672 Caspian Terns from the Little Galloo Island population were found dead from type E botulism (W. Stone pers. comm. cited in Smith 2008). Although, the number of nests reported in 2007, 1580, was similar to the number reported before the outbreak in 2006 of 1589 and numbers exhibited only a moderate decline to 1376 nests in 2008 (New York Natural Heritage Program 2008), future outbreaks would be detrimental and could eventually lead to the extirpation of this nesting colony (Smith 2008). Studies in the Great Lakes have also indicated the presence of environmental contaminants particularly PCBs, TCDD, DDE, mirex, and HCB in Caspian Tern eggs and chicks (Grasman et al. 1996, Struger and Weseloh 1985). These are harmful because they may lead to immunosuppression, reproductive and developmental difficulties in birds as well as egg-shell thinness (Grasman et al. 1996, Struger and Weseloh 1985). Despite this, the Great Lakes the population appears to be reproducing and expanding successfully demonstrating some resilience to current contaminant levels.

Conservation Strategies and Management Practices [-]
Since the colonies with highest reproductive success are found in locations isolated from human disturbance with low predation, best management practices are centered around minimizing disturbance to the nesting area. Successful efforts include the creation of nesting islands away from disturbance, limiting human access, and protecting existing colonies from development pressure. Researchers have sought to limit investigator disturbance by implementing nest covers while visiting the nesting area and even constructing tunnels to allow access to observation blinds without distressing the colony. Taylor and Blokpoel (1996) described the successful creation of nesting islands and rafts in Hamilton Harbour in Lake Ontario and the process they used to encourage the occupation of them. Quinn and Sirdevan (1998) demonstrated that Caspian Terns selected sand as a nesting substrate over stone and gravel and recommend mixing sand with a small amount of pea gravel which is used in nest lining, during habitat creation projects. This research, in addition to the creation of floating nesting platforms, proved effective to establish new colonies on Lake Ontario (Quinn and Sirdevan 1998). In New York, both known colonies occupy islands that are protected and managed for colonial waterbirds. Human activity such as boat-landing and fishing surrounding the islands could disturb breeding birds and should be restricted from April through July. Activities that would negatively affect water quality, increase water temperature, turbidity, or alter depths surrounding the islands could impact spawning and reproduction by fish species in the area (NY State Department of State and NY Department of Environmental Conservation 1993).

Research Needs [-]
Research is needed to identify stopover sites during migration and important wintering areas; both remain largely unknown. Other research priorities for this species include population dynamics especially factors that favor increase and expansion, comparative studies of solitary verses colonial nesting behavior, and studies of reproductive strategies and parental care (Cuthbert and Wires 1999). Research into the genetic structure of North American populations, especially given the disjunct distribution and fidelity to the natal site, are warranted (Cuthbert and Wires 1999). In New York, future inventory efforts are needed to identify new nesting locations assuming the continued eastward expansion in distribution.