Probability of lek collapse is lower inside sage-grouse Core Areas: Effectiveness of conservation policy for a landscape species

Abstract

Greater sage-grouse (Centrocercus urophasianus) occupy sagebrush (Artemisia spp.) habitats in 11 western states and 2 Canadian provinces. In September 2015, the U.S. Fish and Wildlife Service announced the listing status for sage-grouse had changed from warranted but precluded to not warranted. The primary reason cited for this change of status was that the enactment of new regulatory mechanisms was sufficient to protect sage-grouse populations. One such plan is the 2008, Wyoming Sage Grouse Executive Order (SGEO), enacted by Governor Freudenthal. The SGEO identifies "Core Areas" that are to be protected by keeping them relatively free from further energy development and limiting other forms of anthropogenic disturbances near active sage-grouse leks. Using the Wyoming Game and Fish Department's sage-grouse lek count database and the Wyoming Oil and Gas Conservation Commission database of oil and gas well locations, we investigated the effectiveness of Wyoming's Core Areas, specifically: 1) how well Core Areas encompass the distribution of sage-grouse in Wyoming, 2) whether Core Area leks have a reduced probability of lek collapse, and 3) what, if any, edge effects intensification of oil and gas development adjacent to Core Areas may be having on Core Area populations. Core Areas contained 77% of male sage-grouse attending leks and 64% of active leks. Using Bayesian binomial probability analysis, we found an average 10.9% probability of lek collapse in Core Areas and an average 20.4% probability of lek collapse outside Core Areas. Using linear regression, we found development density outside Core Areas was related to the probability of lek collapse inside Core Areas. Specifically, probability of collapse among leks >4.83 km from inside Core Area boundaries was significantly related to well density within 1.61 km (1-mi) and 4.83 km (3-mi) outside of Core Area boundaries. Collectively, these data suggest that the Wyoming Core Area Strategy has benefited sage-grouse and sage-grouse habitat conservation; however, additional guidelines limiting development densities adjacent to Core Areas may be necessary to effectively protect Core Area populations.

Fig 1

(A) Wyoming in relation to the United States. (B) Density of average oil and gas wells per km² (C) 31 sage-grouse Core Areas designated by The State of Wyoming SGEO (version 3) within the distribution of sage-grouse (D) Locations of 2,382 leks archived within the lek database. For our study, only leks surveyed from 1999 to 2013 were used. Collectively, these were the data sets that were used to conduct our analysis.

Fig 2. Observed population trends from male lek counts inside and outside of Core Areas, by year, from 2001–2013 in Wyoming.

The vertical line at 2008 indicates the year in which the SGEO was enacted.

Fig 3. Probability of lek collapse was calculated independently for each year using a Bayesian binomial probability function of the Core Area leks and non-core area leks in Wyoming, 2001–2013.

All probabilities are independent probabilities of collapse, however probabilities have been displayed as continuous for easier viewing. The vertical line at 2008 indicates the year in which the SGEO was enacted. The 95% credibility interval is given for each year.

Fig 4. Probability of lek collapse was calculated using Bayesian binomial probability from 2001–2013 in Wyoming based on leks located 1.61 km (1 mi), 4.83 km (3 mi) outside Core Areas and the Core-Core Area.

All probabilities are independent probabilities of collapse; however probabilities have been displayed as continuous for easier viewing. The vertical line at 2008 indicates the year in which the SGEO was enacted. The 95% credibility intervals have not been included, but all CI’s overlap.

Fig 5. Predicted percent change in Core Area lek attendance as a function of oil and gas development adjacent to Core Area boundaries.

We used the linear model from the regression of Core Area lek attendance for leks within 1.61 km and 4.83 km of the Core Area boundary against oil and gas development density within 1.61 km and 4.83 km outside of the Core Area boundary to predict the percent decline in lek attendance of Core Area leks.