Effect of Group Size on the Startle Response of Geese in the Lake Wingra Watershed
Jenna Ryan, Katrina Stevenson, Angela Traut

Abstract
 
The amount of geese residing in the Vilas Park area has been increasing greatly in recent years.  This increase has caused problems in the Wingra Watershed.  We observed the startle response of the geese towards humans as a function of size of geese groups.  Knowing how the geese will react to humans will help with population control.   We observed the geese over a two month period of time in five of the eight zones in Vilas Park.  Through our observations, we found that there were two distinct group sizes of geese.  The small groups were those less than 100 geese, while the large groups were 100-300 geese.  These groups had measurably different startle responses.  We found that the larger the group, the quicker the geese respond to humans.  This could be caused due to more geese being present to notice the humans.
 
 
Introduction
 
Within the past two decades, the giant Canada goose population has increased dramatically.  A large number of these geese have become urbanized, preferring to live in neighborhoods, golf courses, parks, and “anywhere near water and food” (Clayton 1995).  Vilas Park, near Lake Wingra in Madison, Wisconsin, is a popular environment for both resident and migrant geese.  Vilas Park contains an ample amount of open grassy areas and is bordered by several bodies of water, making it an ideal location for the geese. 
 
In order for a goose to migrate, it must be taught how and where to fly by its parents. If a goose does not migrate, then its offspring will not migrate either.  “Therefore, all following generations of nonmigratory Canada geese will also be nonmigratory, or resident geese, which will stay year-round in the vicinity where they are born” (Link 2005).  Since the offspring of resident geese do not know where to migrate to, they too become resident geese, crowding urban areas.  Furthermore, “Canada geese hatched in urban environments may have very low mortalities due to the abundance of food and relative scarcity of natural predators” (Link 2005).  Urban populations are free to grow at a rapid rate, quickly increasing the effect they have upon their urban habitat. 
 
However, it is not only this resident population that has become a booming problem in Vilas Park, as well as other urban areas across the country.  “Migrating populations (which themselves tend to winter further north each year) often join these resident populations, which apparently serve as ‘decoys’ that attract migrants to urban areas occupied by resident geese” (Lorman et al. 2003).  Resident populations, besides internal growth due to low mortality rates, are increased by additional migrant geese that see the residents and conclude that the area must be a satisfactory place to live.
 
Problems associated with an increased number of urban geese include a large amount of feces on grassy areas and beaches, damage to the turf itself, increased erosion and nutrient runoff, the possible spread of diseases to other animals, and attacks on people (Lorman et al. 2003).  These problems can be greatly reduced by decreasing the goose population.  However, in order to find effective ways of decreasing the population, one must know how they will respond to both the methods and to the people administering the methods. 
 
Urbanized geese have become more comfortable in the presence of humans.  However, they still respond when humans invade their space.  These responses include (Figure 1):  the alert display, where the neck is vertical and straight and the head is horizontal; the bent neck display, where the neck is tucked back and the head is lowered and pointed towards the aggressor; the head forward display, is when the goose extends its neck and holds the head low and points it towards the aggressor; and the head pumping display, where the goose quickly lowers and raises its head in a pumping motion (Link 2005).
 
We studied how group size of geese affected the way the geese reacted towards humans.  From preliminary research, we could not distinguish resident populations from migrant populations, but we did however notice differences in the size of each group in Vilas Park and how that group reacted toward our presence.  In our study, we recorded the geese’s response when we walked toward them. We hypothesized that with a larger group, the geese’s reaction to humans, also known as the startle response, would occur when we were closer to the geese in comparison to a smaller group.  We thought that with a larger group the geese would feel more secure because there are more of them.  Knowing the differences in the response of geese to humans can aide in further research regarding the effect the geese have on the Wingra Watershed.  It can also help with the control of the goose population. Since many populations control methods involve close contact with the geese,  by knowing how geese are likely to react, one can determine how best to approach a particular group of geese based on the size of that group.

Figure 1: Common startle responses of geese

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Methods

We conducted our research over a span of a month and a half in the months of October and November.  We observed the geese about once a week and recorded the time, weather, and what zone of Vilas Park the geese were in each time (Table 1).  Figure 2 is a map of the different zones in the park where we observed the geese.

Figure 2: Map of the zones in Vilas Park

We observed the first group of geese we came upon in Vilas Park, and then moved to any subsequent groups that we encountered during our walk through the park. We choose groups of geese that were not in the water, since we needed to walk up to them and observe their response.  For each observation, we had one person walk at a steady pace towards a group of geese.  That person dropped a set of keys as a marker when the geese first noticed her and some of the geese started walking away (response 1).  She then continued walking and dropped another set of keys when all of the geese in the group started walking away (response 2).  We used a tape measure to measure and record the distances from both responses 1 and 2 to where we determined the middle of the group of geese had been.

Table 1: Observation Information in Vilas Park

Table 2: Group Size, Distances of Responses in meters and Differences in Responses of Geese

Figure 3: Correlation Between Group Size and Distances of Responses

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Results

During our study we observed geese were in five of the nine zones (zones 2, 3, 6, 7, and 8) (Figure 2).  We studied the geese in cloudy weather, sunny, windy, cold, and also rain (Table 1).  After we looked at all of our data, we were able to determine the differences between larger group sizes and smaller group sizes.  The smallest group we had was 30 geese, and the largest group size we had was 500.  There was a distinct difference between the larger groups and the smaller groups (Figure 3).  We used 100 as the cut off for smaller groups, and 300 for larger groups, as this broke the data into three distinct sections.  

We could conclude that with the smaller number of geese we can get closer to them, while the larger number of geese gives their first response quicker (Figure 2).  We noticed when studying the larger group that once a couple of the geese gave their first response, the entire group would follow.  The smaller group size of geese took a lot longer for them to notice us due to the smaller numbers.  The first response for the smaller group was much quicker than that of the larger group.  We found that the same effect happened when we recorded their second response.  The smaller group size flew away quicker than the large group size. The second response we decided would be when the geese actually flew into the water or up into the sky. 

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Discussion

 When observing geese in the Wingra Watershed, we hypothesized that a small group of geese would react to the presence of humans more quickly than a larger group would.  We made this hypothesis based on the general inclination of animals to find security in large numbers.  Our results, however, showed our hypothesis to be incorrect. We actually discovered that geese that traveled together in groups of 300 responded quicker to our presence than groups smaller than 100. We were surprised to find that the smaller groups of geese not only responded slower to the presence of humans in comparison to the larger groups of geese in the Vilas Park area, but that we were able to approach the geese as closely as we did. In a large group, there are more geese to notice that humans are approaching.  Also, the sheer number of geese means that more geese will become frightened, causing the whole group to take notice and respond.  Based on the geese’s responses to the presence of humans, we found that the startle response does change based on the group size of the geese found in Vilas Park of the Wingra Watershed.

Throughout the process of gathering information, our group noticed some potential sources of error.  When determining what specifics were required of the geese’s responses to qualify as first response and second response we established a simple set of guidelines.  For a group of geese, the first response occurred when some geese responded and the second response occurred when most geese responded.  Due to the fact that these guidelines were not measurement specific they were considered a potential source of error. However, due to the nature of our project it would be very difficult to specifically measure the first and second responses in other ways without changing the entire structure of our project.  We also ran into a potential source of error while counting the group sizes of the geese.  This occurred primarily when dealing with large numbers of geese.  Each time we observed the startle response we counted the number of geese the same way. We used binoculars to get accurate results making sure to double and triple count the geese.  The problems that occurred included constant shifting and moving about of the geese and interferences such as trees and surrounding tall grass.  To assist in any potential future students on the startle response of geese it would be useful to indicate the answers as approximately, not exactly, to avoid this inaccuracy.

 Our results have provided some practical implications that may be useful in determining how the geese in Vilas Park affect the Wingra Watershed.  The results provided us with a better understanding of how comfortable geese are with humans.  Clearly the presence of humans had a larger startle response with geese in group sizes of 300 or more in comparison to a group size of 100 or less, which may actually result, as time progresses, in the expansion of the goose population in Vilas Park.  If this does happen it will result in an increase in the amount of feces that will pollute the Wingra Watershed, which will poorly affect the growth of natural vegetation in the surrounding area.  Our results may be helpful in controlling the growing goose population due to a better understanding of the number of geese that occupy the various zones in Vilas Park as well as the knowledge of the two groups’ startle responses to humans.    

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Works Cited

Clayton, Mark. "Gaggles of Geese Give Up the Wild to Become Pests in Urban America." Christian Science Monitor 87 (1995): 14. EBSCOhost. EBSCO. Edgewood College Library, Madison. 28 Nov. 2007. Keyword: Canada geese.

Link, Russell. "Living with Wildlife." Washington Department of Fish and Wildlife. 28 Nov. 2007 <http://wdfw.wa.gov/wlm/living/canada_geeese.htm>.

Lorman, Jim. Giant Canada Geese in the Wingra Watershed: a Preliminary Report. Madison, 2003. 28 Nov. 2007 <http://lakewingra.org/library/docs/1117595700-canada_geese.pdf>.

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