The Institute for Wildlife Studies (IWS), in collaboration with the Santa Catalina Island Conservancy, has started an osprey reintroduction on Santa Catalina Island, California in order to return a key component of the ecosystem to the Channel Islands and southern California. The osprey is currently listed as a Species of Special Concern by the California Department of Fish and Game. Although ospreys once occurred as breeding residents on the southern Channel Islands (Kiff 1980), there are currently no known nesting pairs on the islands. San Clemente Island contained the largest number of nesting pairs, with at least 20 nests found in 1907 (Linton 1908, Kiff 1980). Ospreys also were common on Santa Catalina Island, although no estimates of their numbers can be found (Kiff 1980). However, Howell (1917, as cited in Kiff 1980) reported that on Santa Catalina Island "every detached rock of any height [had] its resident pair".
Osprey numbers appear to have declined starting in the early 1900s, probably due in large part to indiscriminate shooting (Kenyon 1947, Kiff 1980). By the 1930s, ospreys were seldom seen on Santa CatalinaIsland (Willett 1933, as cited in Kiff 1980). Although individual osprey are occasionally reported on Santa Catalina Island, no osprey pairs are known to occur and no nests have been found on Santa Catalina Island since the early 1900s.
Introductions are usually only necessary when existing nesting populations are 300 km or more from historical nesting ranges, making the likelihood of natural re-establishment low (Henny and Anthony 1989). Currently, the closest osprey nesting populations are at the southern end of the Sierra range (Henny and Anthony 1989) and in Baja California (Friedman et al. 1950). Both of these nesting populations are >300 km from Santa Catalina Island. Additionally, although the number of pairs of breeding osprey have increased at the southern edge of their range in California, the breeding range has not extended farther south (Henny and Anthony 1989). These factors suggested that it was improbable that ospreys would naturally re-establish themselves on Santa Catalina Island.
These birds were transported to Santa Catalina Island and placed in a release tower at Thompson Reservoir. The hacking technique has been used successfully to introduce ospreys in other areas (e.g., Hammer and Hatcher 1983, Schaadt and Rymon 1983, Martell et al. 1994), and IWS has been using the technique for over 20 years to reintroduce bald eagles (Haliaeetus leucocephalus) to Santa Catalina Island.
The ospreys remained in the hack tower for about 3 weeks until they were ready to fly. Prior to releasing the birds we equipped each one with U. S. Fish and Wildlife Service leg bands and a backpack-mounted radio transmitter to allow us to monitor their movements. All four osprey fledged from the hack tower. Unfortunately, one succumbed to an unknown illness several days after it started flying. However, the remaining 3 osprey remained healthy and one was seen catching fish less than 2 weeks after it learned to fly.
It is unknown whether ospreys introduced to Santa Catalina Island will be year-round residents or migrants. Ospreys in Baja California are year-round residents (Judge 1983, Peterson 1990), and it is possible that the breeding populations of osprey in California that are nearest to Santa Catalina Island do not migrate long distances (Henny and Anthony 1989). If the ospreys brought to the island for release were from a migratory population, we would expect them to return to Santa Catalina Island or the surrounding area in 2 to 3 years (Zarn 1974). In addition to adding new ospreys to Santa Catalina Island, there is also the possibility that birds released on Santa Catalina Island will repopulate other of the Channel Islands. Furthermore, our releases have the potential to attract other ospreys to the area, as apparently occurred in Minnesota (Martell et al. 1994).
Ospreys in other regions have been negatively impacted by organochlorine pollution, particularly DDE (Wiemeyer et al. 1988). As a result of remnant DDT/DDE pollution off the mainland coast of California (Chartrand et al. 1985, Garcelon et al. 1989), bald eagles on Santa Catalina Island are currently unable to hatch their own eggs successfully (Sharpe and Garcelon 1999). However, bald eagles acquire the bulk of their contamination from the tissues of seabirds and marine mammals (Garcelon et al. 1989). Because ospreys feed almost exclusively on fish, which have low levels of DDE contamination around Santa Catalina Island (Garcelon et al. 1989), we believe that osprey would be able to successfully breed on Santa Catalina Island and the surrounding Channel Islands.
The release in 2000 was used to test the effectiveness of our techniques for releasing osprey on Santa Catalina Island. Because of our successful release, we plan to expand the project to release more osprey over the next few years. The more birds that are released as part of the reintroduction effort, the greater the chances for long-term success of the program.
ACKNOWLEDGMENTS: We thank the Santa Catalina Island Conservancy for assisting with the hack tower construction and for allowing us to conduct the release program on their property. We give special thanks to the the Eagle Lake Ranger District, of the U.S. Forest Service for allowing us to remove the young osprey and for their assistance in accessing the nests.
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