1. The Correlation of Tree Cavity Height and Owl Nesting Habits
Statement of Problem
Materials
Results
Discussion
Tree cavity height is an important factor in the nesting of woodland owls. Which range of tree cavity heights best supports owl nesting?
The materials used in this experiment were: a GPS unit, measuring tape, yellow flagging ribbon, and a camera rig. The camera rig consisted of an ActionPro miniature camera attached to an eight meter telescopic pole. A Galaxy tablet was used to mirror the camera.
The results of the study support the initial hypothesis, as 5.9% of trees in the centimeter range were active.
Overall, the data collected provided new insight concerning the optimal cavity height of owls in Southeastern Arizona. The average active cavity height was found to be 484 centimeters. However, active cavities were found to be anywhere from centimeters in height.
This data suggests that owls can nest at a wider range of cavity heights and at lower average heights than previously believed.
While this wide range may suggest a level of uncertainty in an owl’s preferred nesting height, 55% of data points collected were within the centimeter range.
A major imitation of this study was its sample size. Because of the rarity of active cavities, the activity rates shown in the results may not be precise.
Introduction
Activity Rates at Height Intervals
Small owls found in Southeastern Arizona such as M. trichopsis, M. kennicotti, O. flammeolus, and M. Whitneyi rely heavily on tree cavities. These owls, unlike most birds, do not build their own nests. Instead, they use tree cavities created by woodpeckers, fallen branches, or rot.
Owls need to choose a cavity that is high enough to avoid predation but low enough to provide a safe environment for owlets learning to fly. Therefore, an optimal cavity height range can be determined by scientists. This range can be used by developers in order to preserve optimal nesting sites.
My hypothesis is that the optimal range for owl cavity nesting will be anywhere from 400 to 600 centimeters, as most ground predators will not be able to reach this height.
Table 1: This table displays the percentage of cavities that were active at each height interval
Figure 2: Tree cavities within a plot are surveyed using a camera rig. Photo taken by author
Activity Rates at Height Intervals
Methods
In order to gather data, a fifty square meter plot of forest was flagged out. Then, the trees within the plot were scanned for cavities.
Each time a cavity was found, its location and height were recorded on a data sheet. The camera rig was then lifted into to the cavity so the contents would be shown on the tablet.
Based on the presence or absence of materials like eggshells or feathers, a determination could be made as to if the cavity was active or inactive.
In total, thirty-five plot cavity inventories were taken. This allowed for a sample size of 225 cavities.
Future Implications
This research is valuable because it allows developers to preserve likely owl nesting sites.
A problem with this goal is that the activity rates of cavities at even the optimal range are relatively low. Future research to find the optimal ranges of other nesting criteria is needed in order to find and protect the trees with the highest activity rates.
While it is unlikely that a cavity solely at the optimal height range is active, it is more likely that the cavity would be active if it fits multiple criteria.
Figure 3: This graph displays the total number of cavities and the number of active cavities at each height interval
Heights and Contents of Active Cavities
Figure 1: An uninhabited tree cavity at 445 centimeters. Photo taken by author
Table 2: This table displays the heights and contents of active cavities