Tulsa Audubon Society
Year 2001 Zink Island Least Tern Breeding Survey
Robert J. Harwood
Least Tern Observers: Judy Barto, Bill Carrell, Bob Harwood, Leda Laurence, Jo Loyd, Tomye Mainer, Gail Storey, Suzy Tramel
The least terns breeding success this year was for all practical purposes the same as last year, not very good.
The purpose of the least tern breeding survey this year as other years is to determine breeding success in comparison with previous years. Before this year’s nesting season the U.S. Fish and Wildlife Service, the Corps of Engineers, and the Boy Scouts removed the vegetation from both Zink and North Zink islands. This year the survey extended from May 13 to July 22, almost the same date range as last year. I would like to thank all the members of this year’s survey for all the hours they spent in doing the survey, and their excellent observing and reporting of the least tern data. Also, I would like to thank Neely Lowrie for his excellent advice.
(1) The least tern breeding success this year was for all practical purposes the same as last year, not very good. There were 18 fledged young this year versus 20 last year, and the ratio of fledged young/nests was 0.43 versus 0.44 last year.
(2) No evidence of nesting on North Zink Island was seen; nesting was only on Zink Island.
(3) The vegetation largely grew back during the nesting season.
(4) No clear reason for the poor breeding success this year is evident.
The vegetation should be removed from Zink Island again, and the vegetation residue should be sprayed to prevent grow-back. Additional sand should either be manually added to Zink Island, or added by managing the river flow. Additional investigations of the tern food source should be done to verify the quality of the fish in the river.
The least tern breeding rate this year is virtually the same as last year, 18 fledged young versus 20 last year and 42 nests versus 45 last year (Figures 1 and 3) giving fledged/nests ratios of 0.43 and 0.44 (Figure 2). These results should be considered as being the same because of the impreciseness involved in making the observations. Also, the numbers of adults seen on Zink Island were nearly the same both years, 93 versus 80. Non-flying young data also are similar for both years, 44 this year versus 42 last. An observation on the island by Kevin Stubbs of Fish and Wildlife on June 13 found 48 nests versus 42 nests in observing from the banks, and 11 chicks versus 2 seen from the banks. This kind of variation is expected between the two types of observation. Much better breeding success was attained in 1992 through 1999 when the ratios of fledged/nests ranged from 0.61 to 1.44 and the numbers of fledged chicks ranged up to 46.
Removal of vegetation from the islands was expected to cause increased breeding success this year. However, the rapid growth back of the vegetation may have been a significant factor is keeping the breeding results the same. More aggressive vegetation removal needs to be done before the next breeding season. This year the Canada geese were not observed unduly interfering with the least terns. Questions still remain about possible heavy metal contamination of the fish food supply, and predation of the least tern chicks by birds, reptiles, or mammals. Boaters in the river did not appear to seriously disturb the terns this year, and no people were observed on Zink Island except those authorized. Flooding was not a factor this year as last.
Additional colonies of a few birds were observed on islands at 71st street and ~78th street. These colonies each probably successively fledged a few chicks.
The poor breeding success on Zink Island and the lack of use of North Zink Island still remain unsolved mysteries.
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