Tulsa Audubon Society Year 2000 Zink Island Least Tern Breeding Survey

Robert J. Harwood, Chairman

Least Tern Observers: Judy Barto, Bill Carrell, Bill Foster, Bob Harwood, Ellen Lee, Neely Lowrie, Jo Loyd, Tomye Mainer, Patty Moser, Daphne Parker, Sandra Raley, Ruth Rippetoe, Aline Romero, Suzy Tramel

 

Figure 1

Summary
The Least Terns on Zink Island in the Arkansas River had poor breeding success this year, even worse then last year, which is reason for concern.
Year Fledged/Nests Table
1992 1.44 for
1994 1.18 Fledglings
1995 1.05 per
1996 1.43 Nest
1997 0.62 Chart
1998 1.12  
1999 0.61  
2000 0.44  
Introduction

The purpose of the survey is to determine the breeding success this year of Least Terns on Zink Island in the Arkansas River and to compare with the breeding success past years. This year the survey extended from May 14 to July 22. I would like to thank all the observers for the many hours they spent collecting the data used in this survey and to thank Neely Lowrie, the past chairman of the Least Tern survey, for all his excellent advice.

 

 

 

 

Conclusions

(1) The Least Terns had only poor breeding success this year with an estimated 20 fledged young. Last year there were an estimated 33 fledged young. This year the ratio of fledged young/nests is only 0.44, whereas last year it was 0.61, which was also regarded as low.

(2) Several factors may have contributed to the poor breeding success this year. These include the large amounts of vegetation on the island restricting the amount of sand for nesting, harassment by geese on the island, being disturbed by boats and racing shells too close to the island, and being disturbed by people on the island.

Figure 2

Table for Fledglings Per Year Chart
Year Fledged Young Nests F.Young/Nests Adults
1992 46 32 1.44  
1994 47 40 1.18 85
1995 23 22 1.05 50
1996 30 21 1.43 55
1997 21 34 0.62 80
1998 37 33 1.12 75
1999 33 54 0.61 115
2000 20 45 0.44 80
Recommendations

Several actions should take place to increase the chances for breeding success in the future. Vegetation should be removed from Zink Island and also North Zink Island, although no nesting has been observed on the latter island to date. More sand should be added to both islands. The geese should be removed from the vicinity of the islands. All boats should be kept as far as possible from the islands during breeding season. All unauthorized people should be kept off the islands, especially during breeding season.

 

 

Discussion
The Least Terns had especially poor breeding success this year. The maximum number of nests was estimated at 45 from the observation data (Figure 1), but the number of fledged young was estimated at only 20 from the flying young results. This gives a fledged young/nests ratio of 0.44 (Figure 2). Last year the ratio was 0.61, and the year before 1.12. Last year an estimated 33 young birds were fledged, and the year before an estimated 37 birds were fledged. Figure 2 suggests a general decline in ratio of fledged young/nests the past few years. However, Figure 3 does not show a decline in the number of adults over the past several years, but does show the decrease in numbers of fledged young the past two years. In 1995 and 1997 the numbers of fledged young also were low.

Variations in the Least Tern numbers over a few days on Figure 1 are caused by the observations being made at different times of the day by the different observers, and also by some of the observations being made only from the east side of the river. It should be noted that nests could be detected and counted only when an adult tern was setting on the nest.

Several factors may have contributed to the decline in fledged young this year. We cannot attribute the decline to high water. However, the vegetation on the islands has become increasingly thick and extensive restricting the areas available for nesting. Removing the vegetation and adding more sand could only be helpful. The Tulsa River Parks Authority did spend a day adding sand to Zink Island this spring before the Least Terns arrived, but then had to stop adding sand because of higher river levels. The large number of wild geese in the area, often on the island, could only make nesting difficult for the Least Terns; removing the geese could be beneficial for the terns breeding efforts. Several times boats and racing shells have been observed too close to the island, which could disturb the terns. Also, the evening of July 9 several people were observed out on Zink Island causing an unknown amount of damage. The proposed actions suggested above may contribute to future increased breeding success of the Least Terns and might also lead to nesting on North Zink Island. However, there always could be other natural factors presently not known that also contributed to the poor breeding success this year and the lack of use of North Zink Island.

 

Figure 3

 

 

Table for 2000 Data Chart
Day Adults Nests NF Young Flying Young Total Time
1 0 0 0 0 0 1:00
2 3 0 0 0 3 7:00
5 0 0 0 0 0 10:00
6 3 0 0 0 3 10:30
8 3 0 0 0 3 12:20
9 2 0 0 0 2 9:50
10 9 0 0 0 9 10:00
11 4 0 0 0 4 1:20
12 9 0 0 0 9 8:30
13 24 0 0 0 24 10:30
15 19 9 0 0 19 12:40
16 31 12 0 0 31 1:45
17 35 7 0 0 35 1:30
18 37 14 0 0 37 9:10
19 52 11 0 0 52 9:00
20 58 18 0 0 58 10:30
22 45 28 0 0 45 12:40
23 55 25 0 0 55 7:15
24 79 37 0 0 79 11:00
25 45 10 0 0 45 8:30
26 49 28 0 0 49 7:30
27 70 33 0 0 70 9:00
28 80 42 0 0 80 9:45
29 45 35 0 0 45 12:40
30 31 18 0 0 31 9:20
31 42 34 3 0 45 11:00
33 36 16 0 0 36 10:00
34 49 34 1 0 50 8:45
35 75 41 9 0 84 9:00
36 58 34 0 0 58 1:00
37 45 31 7 0 53 9:00
38 59 38 15 0 74 10:00
40 59 22 22 3 81 9:00
41 72 24 12 0 84 9:00
42 60 33 42 0 102 9:15
43 31 21 5 0 36 12:30
44 30 9 16 0 46 7:30
45 39 19 17 0 56 2:30
46 29 0 9 0 38 8:30
47 34 2 20 0 54 9:00
48 47 5 18 0 65 8:00
49 38 3 20 0 58 7:00
50 12 0 0 1 13 12:30
51 30 2 5 1 36 4:00
52 27 5 7 1 35 11:00
54 29 0 13 10 52 9:30
55 13 0 2 7 22 8:00
56 35 0 6 18 59 8:15
57 13 1 5 10 28 1:30
58 11 0 15 5 31 8:00
60 0 0 0 7 7 8:00
61 5 0 4 4 13 9:00
62 2 0 0 0 2 2:00
63 2 0 0 1 3 7:30
65 3 0 0 5 8 7:15
66 2 0 0 2 4 10:30
68 0 0 0 0 0 10:00
70 1 0 0 2 3 8:45
             

 

 

 

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