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Managing Cormorants in the Eastern Basin of Lake Ontario, 1999

Excerpt from a poster presented at the AOU meeting on August 12, 1999 by Irene Mazzocchi

Co-authors: Farquhar, J.F., Kandel, M., Parsons, G., Adams, C.M., Coleman T.H., Richmond M.

Methods

Little Galloo Island

NYSDEC began treating all Double-crested Cormorant (Phalacrocorax auritus) nests on Little Galloo Island with pure food grade corn oil beginning 6 May 1999. The oiling process was conducted five times, at two week intervals (Table 1). Oil was applied from a back pack sprayer unit in sufficient volume to cover the exposed surface of each egg. An average of 6ml of oil was used per egg.

Gull, Bass and Calf Islands

Nest removal activities on Gull and Bass Islands began in 1994 as part of an effort to restrict the expansion of cormorant colonies to islands other than Little Galloo. In 1997, Calf Island was included in nest removal activities following an attempt by cormorants to establish a colony. Visits to Gull and Bass Islands were made weekly beginning in early May and continued until mid July. On Calf Island only two visits per season were necessary. All ground nests were removed by hand and tree nests were removed with a 6m telescopic pole from the ground or by climbing the tree and prodding with a 3m metal pole. Each nest removed was scattered as much as possible to discourage rebuilding. In 1999, 147 nests were removed from Gull Island and 40 removed from Bass Island.

Results

Little Galloo Island

The number of eggs oiled on Little Galloo Island ranged from 5,015 - 16,310 per trip (Table 1). Peak nest count was 5681 nests recorded on 20 May. Hatching success (number of chicks hatched per egg) for oiled nests was less than 1%. This meets the objective set in the NYSDEC five year management plan to reduce the number of successful cormorant nests on Little Galloo Island by 90%.

Gull, Bass and Calf Islands

Since the nest removal program began in 1994, there has been no successful Double crested Cormorant reproduction on Gull, Bass and Calf Islands. Nesting attempts have varied from year to year with the peak number of nests (including re-nests) removed at 345 in 1997.

Table 1. Egg Oiling on Little Galloo Island, Jefferson County, New York, 1999.
Date # Nests Oiled # Eggs Oiled # Chicks On Ground # Chicks In Trees # Tree & Unoiled Nests Total Nests
6 May 2856 7119 0 0 ? 2856
20 May 5627 16310 0 0 54 5681
3 June 4283 9718 0 0 800* 5083
17 June 3889 7568 12 113 90 3979
8 July 2844 5015 36 106 80 2924

*Due to inclement weather approximately 800 nests were not oiled.


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