In 2005 we were able to successfully field test the protocols for our study. In addition to getting logistical infrastructure in place, we also confirmed that the presence of researchers on Northern Spotted Owl (NSO) territories had no discernable effect on the stress levels of the owls (see Figure 1).
Because of a strong effect of scat sample size on hormone concentration, we used the residuals from a regression of sample mass and corticosterone level for this and all other analyses. Simulated enduro events conducted with volunteer riders in 2005 significantly increased male NSO corticosterone levels relative to controls (Figure 2).
Interestingly, simulated enduros had no effect on corticosterone levels in female NSO (Figure 3)
This is consistent with results from an earlier study conducted by Wasser et al. (1997) in which it was found that male NSO living within a quarter mile of a logging road had elevated levels of corticosterone relative to males with territories further from roads. Females showed no effect of proximity to road on level of corticosterone. So far, no discernable effect of OHV exposure on behavior or reproductive success has been detected, however, sample size from 2005 was small, as it was a poor breeding year for the NSO and the pilot year of the project. At this point, no definitive conclusions can be made. Stay tuned as data from 2006 are collected and analyzed.
Figures
Figure 1
Figure 1: Corticosterone metabolites can be detected in Northern Spotted Owl (NSO) scat approximately two hours after corticosterone is secreted into circulation. Therefore, if the presence of our researchers on the owls' territories represents a significance stressor to the owls, levels of corticosterone would increase approximately 2 hours after our arrival and increase with time spent on territory thereafter. This graph shows each scat sample collected plotted by the time researchers had been on the territory on the X-axis and owl corticosterone level (as a residual) on the Y-axis. It shows that there is no relationship between time researchers spent on the territory on owl corticosterone level. Therefore, we can conclude that the process of collecting scat and behavioral data does not represent a significant stressor to the NSO.
Figure 2
Figure 2: Male Northern Spotted Owl (NSO) showed a significant increase in levels of corticosterone after exposure to an hour long simulated enduro event. Control males, shown on the left, were sampled on the same days with the same protocol without being exposed to OHV traffic. Levels of corticosterone shown in light blue were measured from all individuals sampled in the morning prior to OHV exposure for enduro birds and at the equivalent time of day for controls. Sample sizes are shown in parentheses.
Figure 3
Figure 3: There was no effect of exposure to simulated endo event on levels of corticosterone in female Northern Spotted Owl (NSO). Sample sizes are shown in parentheses.