JoAnne Burch

 Purpose

The purpose of this research experiment was to determine the feeding preference of Aimophila Cassina, a sparrow, for three different types of grasses: Warm Season Grasses, Cool Season Grasses, and Fescue Grass. The Warm Season Grasses were composed of Andropogon gerardi (Big Bluestem), Andropogon scoparius (Little Bluestem), Sorghastrum nutans (Indiangrass), Panicum virgatum (Switchgrass), and Bouteloua curtipendula (Side-Oats Gramma) . The Cool Season Grass consisted of Ladino Clover and Phleum pratense (Timothy) grasses. Finally, the Fescue fields were filled with Kentucky 31 Fescue. In each of the three fields, a bird feeder was placed 5ft from the ecotone and approximately 40ft into the middle of the field. This tested the preferce of birds to the open field as opposed to the ecotome (Hitchcock, 366, 534, 698, 726, 754, 758, 776).

Method

The site for the experiment was Taylorsville Lake State Park. The experimental team worked in conjunction with the Wildlife and Conservation Department in order to set up the bird feeders and develop possible tactics for collecting data. Through prior research on feeding times of birds, it was determined that the best times for observation would be early morning and afternoon (Welty, 98). Park Rangers set up the feeder one week prior to the team’s observation in order for the sparrows to become adapted to the additional food supply. The feed was mixed in order to ensure a diverse bird population. It should be noted that these feeders were only intended to entice the birds and not to be their primary food source. The fields were observed three times in the morning and three time in the evening for an hour each period. The feeders and a 15 foot radius surrounding each were observed to record the number of bird visits. Team members viewed their respective feeder simultaneously so as to insure an accurate representation. The temperature at all six visits remained fairly constant, ranging from 40-60 degrees.

Specifically, the team hoped to determine the grass type and preferred area of feeding (ecotone v. field) most favored by birds inhabiting the Taylorsville area.

Due to inconclusive data, the focus of the project was amended to reflect a hypothetical approach. It was determined that Aimophila cassinii would be the most prevalent species found in the Taylorsville lake area due to seaonal changes and its non-migratory behavior (Welty, 454). Upon further research, it was hypothesized that Aimophila cassinii would select the Warm Season Grasses.

Explanations

A variety of factors were taken into account in selecting Warm Season Grasses as the predicted primary feeding site. Primarily, this hypothesis was based upon seed size and grass height. The Warm Season Grasses, most notably Andropogon gerardi(Big Bluestem), Sorghastrum nutans (Indiangrass), Bouteloua curtipendula (Side-Oats Grama), and Panicum virgatum (Switchgrass), had a significantly larger seed size. The Cool Season Grasses, Phleum pratense (Timothy) and Ladino Clover, were marked by a small seed size. The Fescue field, composed entirely of Kentucky 31 Fescue, had a larger seed size however it was speculated that the thick underbrush offset the advantage of the large seed size. The team speculated that a larger seed size would be an advantage to Aimophila cassinii because it would be more easily spotted. The photos of the seed size allow for easier comparison:

Grass height was another consideration in determining Warm Season as the preferred grass. All of the grasses present in the Warm Season field possessed a significant height advantage compared to the Cool Season and Fescue fields. Both of these fields were notably closer to the ground and therefore not as available. The height of the Warm Season grasses enabled the birds to access the seeds more effectively. Seeds located at a greater height provided the birds with a greater visual range. Additionally, the sparrow would be subjected to fewer ground dwelling predators. Due to possible evolutionary selection pressures, the high location of the seeds would reduce the competition with ground rodents for lower grass seeds. In addition to seed height and size, the grass density also could be a determining factor. Again, the photos of the grasses allow a better comparison:

The density of the grasses plays a crucial role in the birds’ preference for a field. An increase in density creates a hindrance for motility of the sparrow. This obstacle retards the sparrows’ ability to efficiently collect food. The Warm Season Grass field was marked by an absence of low-lying underbrush and therefore would not present a challenge for the sparrow. In contrast, the Cool Season and Fescue fields were highly dense and therefore would be less appealing to the sparrow.

Conclusion

There are many requirements that are crucial for Aimophila cassinii to thrive in its natural environment. If any one of these were inadequate or overabundant it would reduce the likelihood of the sparrow’s presence. The chart below attempts to investigate possible factors that could have accounted for the absence of Aimophila cassinii. The chart begins with what is most crucial in the sparrow’s requirements and then investigates other possible problems.