Milwaukee Gull Populations in Relation to

Distance from Lake Michigan

 

by Patti Homolka

BI 341: Ecology

November 30, 2000

Abstract

A study was performed to test the hypothesis that the Milwaukee area gull populations are greatest near Lake Michigan and decrease as distance from the lake increases. Gulls were counted at three sites of varying distances from Lake Michigan. Each site was visited eight times and each visit lasted the same amount of time. The data obtained showed a negative correlation between distance from the lake and the number of gulls observed. The results of the study supported the hypothesis. Key words: gull, Herring gull, Larus argentatus, Lake Michigan.

Hypothesis and Introduction

The purpose of this study is to test the hypothesis that the Milwaukee area gull populations are greatest near Lake Michigan and decrease as distance from the lake increases.

In the United States, Herring gulls, or Larus argentatus, live near the oceans and Great Lakes. Their diets consist largely of fish, particularly while nesting (Belant, et. al., 1993). In addition, L. argentatus tend to nest in or near the same territory from year to year (Tinbergen, 1960). The hypothesis is based on the premise that L. argentatus lives near bodies of water, eats mostly fish and returns to the same territory every year. They would most likely be found where food is present and near their nesting sites.

 

Methods

Gulls were counted at three sites of varying distances from Lake Michigan. All sites were located in Milwaukee County and were at approximately the same latitude. Data was collected in the parking lots at the following locations: Bender Park, which is on the lake shore, Kohls Department store on South Howell Avenue, which is approximately 5.5 kilometers from the lake shore, and Milwaukee County Sports Complex, which is approximately 11.3 kilometers from the lake shore. The distances from the lake shore were calculated using a Milwaukee County map, its legend and a metric ruler. Each site was visited eight times. There were eight outings in which the sites were visited consecutively. Each visit lasted 10 minutes. Data was collected over a period of ten days and every gull seen was counted.

Data and Results

The data collected was graphed and a correlation test performed, using Microsoft Excel. A negative correlation would support the hypothesis, with a value of -1.0 showing the strongest negative correlation between distance from the lake and number of gulls counted. The test showed a correlation of –0.77 between distance from the lake and number of gulls counted, based on all of the data.

 

 

Table 1. Number of gulls counted during each visit to Bender Park (0 kilometers from lake shore), Kohls Department Store (5.5 kilometers from the lake shore) and Milwaukee County Sports Complex (11.3 kilometers from the lake shore).

Visit number

Number of gulls counted at Bender Park (0 km from shore)

Number of gulls counted at Kohls (5.5 km from shore)

Number of gulls counted at the Sports Complex (11.3 km from shore)

1

4

3

0

2

6

1

0

3

6

6

1

4

15

3

36

5

21

2

1

6

12

1

0

7

9

3

3

8

92

1

4

Average number of gulls counted

20.6

2.5

5.6

 

 

 

 

 

 

 

 

Figure 1. Comparison of the distance from the Lake Michigan and the average number of gulls observed at each distance.

 

Discussion

L. argentatus live near the oceans and Great Lakes in the United States, and eat mostly fish (Belant, et. al., 1993). Other food sources include garbage from landfills, intertidal organisms and other sea birds (Belant, et. al., 1993, and Pierotti, et. al., 1991). Gull sightings could be expected at some distance from the lake, due to the presence of garbage. However, most gulls would most likely be spotted closer to the lake, since they eat mostly fish.

The observed behavior of the gulls varied from site to site. All gulls observed at the site that was 11.3 kilometers from the lake were flying east. Those seen 5.5 kilometers from the lake were flying in various directions or sitting on top of light posts in the parking lot. The gulls observed at the lake shore were swooping into and out of the water, flying in circles, or flying parallel to the shore line. Those seen farthest from the lake may have been coming from a landfill or another body of water. There are a few small lakes west of the site that was farthest from the lake. In addition, the third set of visits occurred late in the afternoon, and the site farthest from the lake was visited last. The gulls seen could have been returning to their nesting spots, which is a possible explanation for the abundance of gulls seen flying east during that visit.

There was a moderate negative correlation between distance from the lake and the number of gulls counted. The data collected and negative correlation support the hypothesis that Milwaukee area gull populations are greatest near Lake Michigan and decrease as distance from the lake increases.

 

 

References

Belant, J. L., Seamans, T. W., Gabrey, S. W. and Ickes, S. K. (1993). Importance of landfills to nesting Herring Gulls. The Condor. 95: 817.

Pierotti, R. and Annett, C. (1991). Diet choice in the Herring Gull: constraints imposed by reproductive and ecological factors. Ecology. 72: 319.

Tinbergen, N. (1960). The Herring gull’s world. New York: Basic Books, Inc.