Conservation Endocrinology
Northern Spotted Owls © Folk Photography
The Northern spotted owl (NSO), Strix occidentalis caurina, is the flagship threatened species of the Pacific Northwest. Federally listed under the Endangered Species Act in 1990, the NSO continues to decline at a rate of about 7% throughout its range. Despite the fact that the NSO is one of the best-studied wild vertebrate species in the world, causes of its decline remain controversial.
Our Center has developed measures to help assess the relative impacts of pressures such as barred owl invasion, habitat loss and anthropogenic disturbance in NSO. We were the first to develop non-invasive fecal hormone measures of physiological stress (glucocorticoids), reproductive activity (sex steroids) and nutritional state (thyroid hormones) in NSO. Combined, these measures provide a comprehensive profile of NSO physiological health that can serve as a powerful diagnostic tool in correlational and experimental studies of disturbance impacts. One of our largest studies employs these tools to document impacts of off-highway vehicle and road exposure on the NSO.
Off-highway vehicle (OHV) use has more than tripled in the last decade and continues to gain in popularity. Finding ways to manage recreation that better protect threatened and endangered species is a high priority for USDA Forest Service and US Fish and Wildlife Service. We are measuring the effects of OHV use on the Northern spotted owl (NSO) in the Shasta-Trinity and Mendocino National Forests of northern California, in collaboration with these federal agencies and with motorcycle non-profit groups like Blue Ribbon Coalition. We combine correlational and experimental approaches and measure behavior, annual reproductive success and a suite of fecal hormones that include stress steroids (glucocorticoids), sex steroids (testosterone and estrogen) and metabolic hormones (thyroid hormones).
METHODS
Correlational approach:
Shasta-Trinity and Mendocino National Forests are managed to contain areas of both high and low/no OHV use. Our study compares hormone levels, behavior and annual reproductive success among NSO pairs in comparable habitat with high and low regular exposure to OHV use. Collaboration with bioaccoustical engineers at Hubbs Seaworld enabled us to quantify vehicle use on the roads closest to our territories. This allows us to treat exposure as a continuous variable and test for dose-response effects
Experimental approach:
Twice during the breeding season, once in May and again in July, NSO in both high and low OHV use areas are experimentally exposed to an hour of motorcycle use between 8:00 and 12:00 in the morning. All scat from all NSO on the territory are collected throughout the day. Additionally, behavior is recorded during three hour-long focal watches. Identical data collection is conducted on control pairs in high and low OHV use areas that do not receive the experimental OHV exposure.
The intensity of the motorcycle exposure simulates what occurs during “Enduros”, popular events in which large numbers of motorcyclists ride hard for long distances on National Forest trails. Our simulated enduros are conducted by volunteers from the local OHV community. Volunteer interns from the Student Conservation Association put in long hours to assist with data collection.
Preliminary Results:
Exposure to an hour-long simulated enduro significantly increases fecal glucocorticoids in NSO (Fig.1). Further males are more sensitive than females and both sexes are more sensitive in May than in July (Fig. 2). In May, breeding NSO females spend most of their time incubating while males are responsible for feeding themselves, their mates and their offspring for the first ten days after hatching. Our results suggest that disturbing males at this time may have more impact than later in the season when both members of the pair share the responsibility of feeding offspring. Managers are using these results to limit OHV use in such a way as to best protect breeding NSO.
Figure 1: Male, but not female, fecal glucocrticoid levels were significantly higher than controls after an hour of experimentally applied motorcycle exposure.
Figure 2: Increase in fecal glucocorticoids in response to an hour of experimentally applied motorcycle exposure is stronger in May than in July.
Project 2: IMPROVING SURVEY TECHNIQUES FOR THE SPOTTED OWL
Improving Spotted Owl Surveys
Marvin finds a Spotted Owl roost by the scent of owl pellets.
Without question, one of the most serious threats facing the Northern spotted owl is the recent range expansion of another closely related owl species, the Barred owl (BO), Strix varia. Because BOs may attack and kill NSO, NSO are known to vocalize less when around BOs. This poses a serious problem for the manager whose primary means of establishing NSO presence is NSO vocal response to simulated calls. When repeated vocalization surveys yield no NSO vocal response for three consecutive years, the territory is considered unoccupied and habitat protection is lifted. However, vocalization survey results may be unreliable if NSO are unlikely to vocalize due to BO presence. We are addressing this problem by developing a new survey technique that relies on detection dogs trained to locate owl pellets by scent.
In the spring of 2008 a single detection dog, Marvin, was trained to locate spotted owls by the scent of their pellets and feces. Initial training was conducted at the Center training facility in Pack Forest. Validation work occurred on sites in Shasta-Trinity that are used in our long-term OHV study. We used the best available habitat selection model (Zabel, et al 2003) to identify 18 two km2 search cells with high probability of owl occupancy throughout our study area in sites where we know current NSO locations (although dog handlers remained blind). Marvin successfully located NSO roost sites on 17 of these 18 sites. On one site where he was unsuccessful, the owl was subsequently located outside of the grid created with Zabel’s model. In two cells Marvin found spotted owls that hooters had failed to locate. Most impressively, while it took hooters 63 visits to successfully locate NSO, it only took Marvin 21 visits to find the same pairs. This suggests that incorporating detection dogs into survey protocol can not only reduce bias in the presence of barred owls, but can increase surveying efficiency by three-fold. US Fish and Wildlife has hired the Center’s dog handlers to survey for spotted and barred owls throughout Shasta-Trinity and Mendocino in 2009 and Washington Forest Law Center is seeking funds to have dogs survey Washington state as well.
Other small-scale studies by our Center on NSO in Washington, Oregon and California examine how our physiological health measures vary with proximity to road but also with other land use practices where barred owls are also present, in collaboration with researchers conducting long-term demographic studies throughout the NSO range.
NSO with territories closest to roads have higher fecal glucocorticoids than owls with territories further from roads. Morever, fecal glucocrticoids appear to increase in a dose-dependent manner as proximity to road increases. Consistent with this we also found that NSO in National Parks have lower fecal glucocorticoids than NSO in adjacent National Forests, despite comparable numbers of barred owls in adjacent areas.
Table 1: Summary of outcome for each site surveyed with detection dog. Sites where handlers simulated spotted owl vocalizations are indicated by “Vocalized” in “Notes”. Auditory and visual confirmation were accomplished by either the dog handler and orienteer at the time the dog located the roost or by an independent crew using vocalization survey methods within two weeks.