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Reproductive Success of Ospreys at Two Sites in Connecticut Donna Christine O'neill

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Reproductive Success of Ospreys at Two Sites in Connecticut Donna Christine O'neill Connecticut College Digital Commons @ Connecticut College Biology Faculty Publications Biology Department 7-1998 Reproductive success of ospreys at two sites in Connecticut Donna Christine O'Neill Robert A. Askins Connecticut College, [email protected] Follow this and additional works at: http://digitalcommons.conncoll.edu/biofacpub Part of the Terrestrial and Aquatic Ecology Commons Recommended Citation O’Neill, D. C. and R. A. Askins. 1998. Reproductive success of ospreys at two sites in Connecticut. Connecticut Warbler 18: 120-132. This Article is brought to you for free and open access by the Biology Department at Digital Commons @ Connecticut College. It has been accepted for inclusion in Biology Faculty Publications by an authorized administrator of Digital Commons @ Connecticut College. For more information, please contact [email protected]. The views expressed in this paper are solely those of the author. REPRODUCTIVE SUCCESS OF OsPREYS 121 REPRODUCTIVE SUCCESS OF OSPREYS AT peake Bay (McLean and Byrd 1991). Sibling aggression and brood TWO SITES IN CONNECTICUT reduction, which were common in Chesapeake Bay Ospreys, are often caused by food shortage, but are rarely observed in Ospreys with no food stress (O'Conner 1978; Stinson 1979; Poole 1984). Donna Christine 0' Neill and Robert A. Askins Also, during the nesting months the male Osprey does 99.9% of the hunting for his family (Poole 1989). Food stress could be an indi­ red caU$e of the nest failure of Ospreys; if the male camlOt find Abshact enough food, the female may be forced to hunt also, thereby leav­ Nest success rates and rates of fish delivery to nests were deter­ ing eggs or chicks vulnerable to predation. mined for two large Osprey populations in COlmecticut, one at There were 106 active Osprey nests (nests with eggs) in Con­ Groton Reservoir, Groton, and one at Great Island, Old Lyme, dur­ necticut during 1996 and 131 active nests during 1997 (Victoria ing 1996 and 1997. Between 1993 and 1996 these Osprey popula­ 1996, 1997). The last stronghold for nesting Ospreys in Connecticut tions had substantially different rates of nest success. Great Island during the DDT years was Great Island, a salt marsh located in Ospreys fledged few young while Groton Reservoir Ospreys had Old Lyme. Historically, the densest colony of Ospreys in COlmecti­ good nest success. During 1997, however, fledging rates were simi­ cut has been located in this marsh, and the nests at this site have lar at the two sites. In 1996, low nest success at Great Island 're­ had a high success rate. DUring the late 1970's and into the 1980's, suited from high predation rates, probably due to raccoons. The when Ospreys began to recover from organochiorine poisoning, higher nest success rate at this site in 1997 appears to be due to low Great Island Ospreys continued to increase in numbers and to re­ predation rates because of the installation of new predator guards produce effectively. Since 1991, however, the number of successful on all nest platforms. There was no evidence of raccoon predation nests on Great Island had declined dramatically, falling to zero in at Groton Reservoir in either year. In 1996 Ospreys delivered Hsh 1993 and remaining low through 1996 (Victoria 1996; Figure 1). The to their nests at a similar rate on Great Island and Groton Reser­ number of nesting Osprey pairs on Great Island remained high, voir. In 1997 Great Island Ospreys made more Hsh deliveries to but their nests produced few fledglings. their nests than Groton Reservoir Ospreys. Groton Reservoir in Groton, Connecticut has a similar number The Osprey (Pandion haliaetus) became a symbol of the environ­ of nesting pairs to the Great Island population. The Groton Reser­ mental movement during the 1960's and 1970's. Several studies at voir Ospreys have been very successful at producing young during that time showed that this once abundant fish hawk had declined the same time period that the Great Island Ospreys were reproduc­ radically in numbers. In the Connecticut River estuary and sur­ ing poorly (Figure 1). Great Island Ospreys Hsh mostly on Long ls­ rounding areas, more than 200 active Osprey nests were docu­ lalld Soulld and surrounding brackish estuaries, while the Groton mented in 1940, but by 1970 only eight active nests remained Ospreys appear to be Hshing mainly at the freshwater reservoir (Spitzer 1980, as cited in Poole 1989). The Osprey's decline was where they nest (persollal observation). eventually traced to the chemical DDT and other organochlorines New England Ospreys liVing along the coast apparently rely that were commonly used as pesticides and routinely sprayed on mainly on three species of fish; winter flounder (P/euronecles marshes to control mosquitoes during the 1940's and 1950's (Ames americanus) make up 50% of the bird's diet, Atlantic menhaden 1966). Since the use of DDT and other insecticides was balmed in (Brevoortia tyrannlls) account for 20% and river herring (A/osa spp,) the 1970's, Osprey numbers along the East Coast have been in­ account for 20% (Poole 1989). Survey trawls by the Connecticut creasing (Spitzer et a!. 1978). Departulent of Environulental Protection, Fisheries Division, In some areas, such as the Delaware Bay and the Chesapeake showed that the abundance of winter flounder off the Connecticut Bay, Osprey populations are not making a full recovery. Predation coast in 1995 was the lowest since data collection began in 1979 by the Great Horned Owl (Bubo virginian us) was advanced as the (Simpson et a!. 1995; Figure 2). The decrease in winter flounder co­ most likely cause for nest failures along the New Jersey side of the incided closely with the initial decrease in llest success at Great ls­ Delaware Bay (Steidler et a!. 1991), while food shortage and sibling land. If the prey species that makes up 50% of the Osprey diet aggression were deemed the reason for nest failures in the Chesa- was less available to Ospreys at Great Island, this might affect 120 The COIUlccticut Warbler, VoL 18, No.3, July 1998 122 O'NEIL ET AL. REPRODUCflVE SUCCESS OF OsPREYS 123 3 - ~~ -Greallsland nest success. Moreover, the Osprey population at Great Island is _Groton Reservoir large, so there might be many males trying to find enough food for their families in approxinlately the same area. In contrast, the il 2,5 c Groton Reservoir Ospreys apparently feed mainly on freshwater ~ fish, so they would not be affected by the decline in fish popula­ • 2 ~ tions in Long Island Sound. ,'"c This study focused on comparing the diets of Ospreys at Great 0 1.5 • Island 'and Groton Reservoir. The main goal was to determine '0'" . whether the amounts of fish delivered to nests at the two sites •" were similar. Also, observations on any human and animal activity ",E c that might affect the Ospreys were recorded to attempt to deter­ • 0.5 ., • mine whether there are other reasons that Great Island Ospreys ~'" were unsuccessful at breeding while Groton Reservoir Ospreys ~ ,.- 0 were successful. 1985 1987 1989 1991 1993 1995 1997 Study Areas Figure 1. Average number ofyoung fledged per active nest at Great Island Great Island is a 122-hectare salt marsh located in Old Lyme, and Groton Reservoir, Connecticut, 1985-1997 (from Victoria, 1997). Connecticut. It is separated from the mainland by about 30 meters. It is easily accessible to animals like whitetail deer (Odocoilells virginianlls) and raccoons (Procyon lotor). The area is also heavily used by people during summer weekends for recreational activi­ 90 ties like canoeing, kayaking, fishing and crabbing. Ospreys nesting 80 on Great Island use artificial nesting platforms which are about 4 ~ ";'., meters high. Nest platforms are within sight of each other. Almost .. 70 all nests on Great Island are equipped with metal sheets designed Cl ..~ to keep ground predators out of the nests. These metal sheets wrap 80 ..,.. around the nesting poles immediately underneath the platforms. c 50 There were 14 nesting pairs of Osprey on Great Island during 1996 "0 =~ and 16 pairs in 1997. During both years there were several young ~ 40 birds that did not build nests. In 1997, Great Island was closed to 'j; 30 recreational activity by the Department of Environmental Protec­ -0 tion during the incubation and hatching periods, from May 26 to Gi J:l 20 July 7. E The Groton Reservoir is a system of interconnecl(~d freshwater Z " 10 reservoirs covering about 216 hectares. The area is fenced and <> locked to keep the public out but is heavily used by Groton town 1985 1981 1989 1991 1993 1995 1997 employees. Trucks and lawnmowcrs arc constantly passing by the Osprey nests. Fishing.. hunting and aU types of water n~crealion arc prohibited in the Groton Reservoir. Groton Ospreys use converted Figure 2. Geometric mean of abundances for 3-11 year old flounder per tow for Long Island Sound along the coast of Connecticut, 1985-1997. (from utility poles that have platforms attached on the tops for nest sites. Penny Howell, CT DEP Marine Div., personal communication, 1998) These poles are 9 meters high, so the Groton Ospreys were nesting much farther off the ground than the Great Island Ospreys. The Groton poles are not eqUipped with predator guards. The nests are The COlUlecticut Warbler, Vol. 18, No.3, July 1998 124 O'NEIL ET AL. REPRODUCTIVE SUCCESS OF OsPREYS 125 located farther apart than those at Great Island; in many cases, to analyze the frequency of fish deliveries. The allalysis was based they are not within sight of other Osprey nests. Some of the poles on whether fish were or were not delivered during an observation are close to electrical high tension wires, but none are directly con­ ,.
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