The Sublette County Journal
Volume 4, Number 14 - 12/2/99
brought to you online by Pinedale Online
"Pinedale/Jackson Region Sage Grouse Job Completion Report, 1996-1998"
Pinedale/Jackson Region Sage Grouse
Job Completion Report
Period Covered: January 1, 1996 - March 1,1999
Prepared By: Doug McWhirter
The management of sage grouse has become, and will continue to be increasingly scrutinized, especially as populations continue to decline throughout much of the range of this species. Thus, the collection and analysis of sage grouse population data has never been more necessary. This report summarizes these data collection efforts in the Pinedale/Jackson Region for the period 1996 through 1998, beginning with lek surveys in 1996 and continuing through the winter of 1998-1999.
Data collected within the Pinedale/Jackson Region has consisted of 1) lek surveys, 2) brood surveys, and 3) wings of birds killed by hunters. Lek surveys are used to assess active/inactive status and trends in lek attendance by males. Aerial surveys are used to locate new leks and determine active/inactive status. Only ground observations were used to determine maximum attendance by males. Brood surveys give a measure of productivity in the form of the number of chicks/hen. Cumulative observations, and data gathered from horseback and vehicle routes were used to calculate productivity. Productivity is also calculated using sex/age information from wing barrel collections. Wings were collected in barrels distributed throughout Upland Game Management Areas 3 and 7 (Figure 1). These collections allow the composition and distribution of harvest to be determined. Hatching dates and the percentage of successful nesting hens can also be determined from these samples. Data collection protocols follow that recommended by the Western States Sage Grouse Technical Committee (Appendix A).
Harvest and hunter information is obtained through a mail questionnaire of bird hunters in Wyoming. These data are compiled by Upland Game Management Area. Because Upland Game Management Area 7 lies within portions of both the Green River and Pinedale/Jackson Regions, harvest data does not correspond directly to areas where lek and brood surveys are conducted within the Pinedale/Jackson Region. It must be recognized that harvest information from the questionnaire represents a larger area than the area with the Pinedale/Jackson Region where sage grouse population data is collected.
This analvsis is broken into 5 distinct sections: 1) leks, 2) nesting, 3) hatching, 4) brood production, and 5) harvest. Included are information from Upland Game Bird Management Units 1, 2, 3, and a portion of Unit 7.
In 1996, 33 active leks and 34 inactive leks were surveyed. In addition, 60 historical leks were not surveyed. In 1997, 38 active leks and 25 inactive leks were surveyed, while 43 historical leks were not surveyed. In 1998, 61 active leks and 36 inactive leks were surveyed, while 49 historical leks were not surveyed. As a result of the 1998 lek surveys, it has been determined that there are 146 known leks within the Pinedale/Jackson Region (Appendix B).
Perhaps the most routinely surveyed set of sage grouse leks within the Pinedale/Jackson Region is in Jackson Hole. Total male attendance on these leks has shown a profound decrease since 1990 (Figure 2). This is quite different from the increased numbers of males observed on leks in the Pinedale/Big Piney area (Figure 3). Part of the reason for the apparent recovery of strutting males in the Pinedale/Big Piney area is the discovery of~new" leks. In 1996, 4 leks went from active status to inactive status and 2 leks went from inactive status to active status in the Pinedale/Big Piney areas, while no new leks were found. In both 1997 and 1998, 6 leks went from active status to inactive status and 5 leks went from inactive status to active status each year. In 1997 4 new leks were found and in 1998 16 new leks were located. This increase in new leks (which is primarily a result of increased sampling effort) coupled with a true increase of birds on existing leks, is responsible for the dramatic increase seen in male attendance in 1998 on the Pinedale/Big Piney leks.
When the average number of males per active lek is examined, however, the trend remains, as the number of males per lek in Jackson Hole has continued to decline (Figure 4) while some recovery has occurred in 1997 and 1998 on Pinedale/Big Piney leks (Figure 5). In fact, birds on the Pinedale/Big Piney leks have increased 153% from the low experienced in 1996, while attendance at the Jackson Hole leks have declined to their lowest point ever.
The percentage of successful nesting hens was determined by analysis of wings collected from birds killed by hunters in September. Hens were successful nesters if they were molting primaries 5, 6, 7, or 8. The added energetic cost of raising young delays molting of these feathers. Unsuccessful nesters were already molting the ninth and tenth primaries. This merely indicates whether or not a hen produced young, not that she successfully reared the chicks.
There has been long term variation in nesting success in this area (Figure 6). The percentage of successful nesting hens decreased from 94% in 1990 to 74% in 1995, and continued to decline to 68% in 1996 and 41% in 1997. A slight increase to 54% was seen in 1998 (Figure 7). The 1990-1998 average is 71%, only slightly less than the long term average of 78% obtained from averaging all available data from 1958-1985. It is difficult to reconcile this dramatic decline in nest success with the apparent recovery in male attendance seen on leks in 1997 and 1998.
Differential nesting success between yearling and adult females was observed in 1997 and 1998
(Figure 8). Adult hens had noticeably higher nesting success rates than did yearling hens. During
1994 through 1996, yearlings and adults had verv similar nesting success. The data collected in 1997 and 1998 more closely approximates that of 1991, 1992 and 1993.
Average hatching date, as determined by analysis of juvenile wings collected from hunters varies from year to year, but always peaks sometime in June (Figures 9-Il). As seen during the period from 1990 to 1996, the earliest hatching date recorded from 1996 to 1998 was during the second week of May and the latest was the last week of July.
Peak hatch dates in 1996 and 1998 were quite normal for this area (based on 1990-1996 data), which was essentialIy mid-June, with the peak actually occurring during the third week of June. The peak hatch in 1997, however, was skewed further to the last week of June. Perhaps climatic conditions (a cold, wet spring) during early nesting caused nest failures, forcing greater numbers of hens to renest. Future analysis will examine the relationship between weather conditions and hatching dates for the data set collected since 1990.
Brood surveys consist of incidental observations coupled with routes traveled specifically for brood counts. Results vary with effort, but the more systematic method employed since 1994 has produced samples of more than 100 broods (Figure 12).
Productivity, as measured by the average number of chicks per hen, declined dramatically from 3.5 in 1990 to 1.3 in 1995 (Figure 13). Some recoverv in the number of chicks per hen was observed in 1996, but returned to previously low levels in 1997 and 1998. As was stated in the 1990-1996 Sage Grouse Job Completion Report, this is a major departure from the average of 3.4 chicks per hen seen from 1958 to 1975. The average from 1991 through 1998 was 1.7 chicks per hen (Figure 14).
Sage grouse harvest has declined dramatically over the last 10-15 years (Figure 15). In Upland Game Management Areas 3 & 7, harvest declined approximately 81% from 1983 to 1997. Hunter numbers have followed this same trend, as 74% fewer hunters took to the field in 1997 versus that seen in 1984 (Table 1). Hunter days dropped from a high of 10,181 in 1983 to a low of 3,428 in 1997, a decline of 66%.
Composition of harvest was determined by examination of wings collected from hunter killed birds during the fall hunting season. Total number of wings collected is shown in Figure 16. The dip in 1995 coincides with the first year the season opening date was shifted from September 1 to mid-September. A breakdown of harvest composition from 1996 through 1998 is given in Table 2.
The decline in hunter participation and harvest can be attributed to both a decline in the population and changes in hunting season dates which were designed to reduce the vulnerability of hens with broods and the potential harvest. One piece of information obtained from these wing collections is an estimate of brood productivity (i.e the number of chicks in the harvest versus the number of hens. When this estimate is compared to brood productivity estimates obtained from survey efforts, a noticeable difference is seen in the data sets. Brood survey estimates are usually higher than those obtained from wing data (Figure 17). Presumably, this is due to the fact that brood surveys contain samples taken from late June through late August and that some chick mortality is occurring prior to when wings are collected during the mid-September/early October hunting season.
Due to the difficulty of obtaining adequate sample sizes from brood surveys, and the somewhat inflated estimate that early season brood counts can give, it is suggested that wing data continue to be used to estimate productivity. Brood surveys should also continue, as the two sets of data could be used to compliment each other and reveal trends in chick mortality.
As discussed in the 1990-1996 Sage Grouse Job Completion Report, there has been a general declining trend in percentage of juveniles in the harvest, particularly since the mid- 1970s (Figure 18). Representation of juveniles in the harvest seems to have stabilized, but remains well below that seen during the years from 1960 to 1975. Consequently, the proportion of the harvest comprised of yearlings and adults has generally increased, particularly that of adult and yearling females (Figure 19). A dramatic difference is seen in the composition of the harvest between the period prior to 1975 and the period following 1975 In 1975, the percentage of juveniles in the harvest decreased noticeably, while the proportion of adult and yearling females in the harvest increased noticeablv. It is not coincidence that 1975 was the initiation of the poor brood productivity that has been affecting this population ever since (see Figure 14).
Harvest of sage grouse was broken out by week to assess the timing of harvest (Table 3). During the years the season ran from September 1 through September 30, most (60%-70%) of the harvest occurred in the first week of the season. After that, harvest declined dramaticallv. The 1995 season, which did not open until September 16 and closed on September 30, saw an equal amount of hunting pressure in each of the two weeks. Harvest pressure in 1997 showed a similar trend. The 1996 and 1998 sage grouse hunting seasons, however, revealed that substantially more harvest occurred during the first week of the season than the second.
Observations of wintering sage grouse from the winters of 1996, 1997, and 1998 are provided in Appendix C. The compilation of this data with that recorded in the 1990-1996 Sage Grouse Job Completion Report should allow for the identification of several important sage grouse wintering areas. Information gleaned from recent and proposed sage grouse research projects will also be helpful in delineating these important areas. There is also some potential to identify potential sage grouse wintering areas using GIS technology. An analysis incorporating data layers such as slope, aspect, and vegetation type could yield possible winter ranges. This could further be refined with digital snow cover data. All of these data layers are currently available for the Upper Green River Basin and should be used in this type of analvsis.
The Mesa Sage Grouse Study
As a result of funding provided by Ultra Petroleum, The Mesa Sage Grouse Study was initiated in 1998. As of this time, the first annual report has been completed (Appendix D). Initiation of this project involved the following:
- 39 females and 21 males were captured and radioed on 6 different leks (3 undisturbed" leks and 3 "disturbed" leks) during the spring of 1998. Disturbed leks have an increased level of disturbance associated with them, in this case primarily roads accessing a natural gas field.
- Weekly locations were obtained from April through August, 1998. From September, 1998 through May, 1999 three telemetry flights were performed.
- At each location, habitat types were recorded.
- At nest sites and brood rearing areas, vegetation data was collected.
- 20 juveniles (15 females, 5 males) were captured and radioed in August, 1998.
Highlights from this study include the following results:
- Males moved very little from March through June and remained near the lek sites. Some interlek movements were documented (28.5% of collared males relocated to different leks). By July, males and broodless females moved to summering areas (primarily irrigated hay meadows). Six males were killed by predators by summers end.
- Five of the 39 females were lost to predation.
- Twenty-eight of 36 collared females initiated nests (2 renests, 1 hen nested 3 times) for a total of 32 nest attempts. Eighteen of 32 nests lost to predation. Fourteen successful nests (at least one chick was hatched from nest), for an estimate of 39% nesting success.
- A total of 68% of the radioed hens nested within a 2.0 mile radius of a lek. When broken out, however, 89% of the hens from undisturbed leks remained within the 2.0 mile radius while only 47% of the hens from disturbed leks remained within 2.0 miles.
- A couple of the more unusual movements include that of a hen who moved 60 air miles to nest near Green River Lakes and a hen that moved 30-40 air miles to nest near Black Butte.
- Hens remained within 1.0 mile of the nest during early brood rearing (first three weeks of life). Taking into account the range of hatching dates, this would be approximately late May through late July. Four broods were lost to snow and cold temperatures during this time.
- Eleven hens managed to get chicks through to late brood rearing. These birds moved to summering areas (irrigated hay meadows, riparian areas near sagebrush). All but 2 hens moved off The Mesa. Some hens moved their broods as far as 10 miles, to irrigated hay meadows on the CL Bar Ranch. Most hens reared their broods just off The Mesa, many of them returning nightly to roost in the sagebrush uplands on the flanks of The Mesa.
- The average clutch size was 7~8 chicks. One month later, it dropped to 2.7 chicks. When all marked females were included, brood productivity was only 0.72 chicks/hen.
- Only 1 bird was harvested during the 1998 hunting season.
- On the November 19, 1998 winter flight, 54 birds were located. Two of these, both males, remained north of The Mesa. Twenty-three either moved back or remained on The Mesa, while 29 birds had moved south of The Mesa to winter ranges located south of the New Fork River and west of Highway 191. Wintering birds were found both to the north and south of Wyoming Highway 351.
- By the time of the January 30, 1999 flight, the 2 males that were wintering north of The Mesa were now on The Mesa. Little movement occurred since the November flight (only 6 more birds moved off The Mesa to areas south of the New Fork River).
- Eight grouse (3 males, 2 females, 3 chicks) had died between late August and the November, 1998 flight. Five more grouse died during the period between the November, 1998 flight and the January, 1999 flight.
The University of Wyoming Cooperative Wildlife Research Unit initiated a study of the sage grouse population in Jackson Hole in April, 1999. The project is being conducted in cooperation with the WGFD, National Park Service, and the National Elk refuge. A study proposal is included in Appendix E. Objectives of this research include the following:
1) Identify and vegetatively quantify seasonal habitats used by sage grouse based on reproductive status (nesting, brood rearing, late summer, and winter habitat selection).
2) Quantify the immediate effects of management practices and development throughout the park.
3) Assess the impacts of predation on sage grouse productivity.
4) Assess the impacts of ungulate grazing on the sagebrush dominated portions of the park.
Sage grouse in the Pinedale/Big Piney areas seem to have experienced a slight recovery during the years from 1996 to 1998. Total number of males surveyed and average number of males per lek both increased considerably. The sage grouse of Jackson Hole, however, were not as fortunate, as total male attendance and average number of males per lek continues to drop and in fact, has never been lower since records have been kept. Nesting success continued to decline in 1996 and 1997, with a slight recovery in 1998. These declines in nesting success make it hard to explain the increase in male attendance at leks during 1997 and 1998. Perhaps chick survival was better during these years, compensating for poor nest success (slight improvement of brood productivity was observed in 1996, but declined again in 1997 and 1998). The increased brood productivity seen in 1996 caused the percentage of juveniles in the harvest to increase that year. The proportion of juveniles in the harvest declined following the decline in brood productivity seen in 1997 and 1998. Although appearing to have stabilized or begun a slight increasing trend, the representation of juveniles in the harvest still does not come close to approximating that seen from 1960 to 1975. Consequently, the representation of adult and yearling hens in the harvest remains above that seen prior to 1975. While the composition of the harvest has noticeably changed, so has total harvest, declining roughly 80% over the last 15 years.
It appears as although some recovery has been initiated in the last three years, this grouse population is still suppressed due to poor chick survival. In addition, nesting success may also be a factor which was not given as much importance in the l990~l996 Sage Grouse Job Completion Report, as success rates did not appear to be beyond that of past fluctuations. The continuation of depressed nesting success seen from 1996 to 1998, however is cause for concern. Although the composition of the harvest may be somewhat undesirable, the effect of the dramatically reduced total harvest may outweigh the adverse impact of increased adult/yearling female harvest. There must be some level of compensation occurring to allow for the increased male attendance observed the last few years.
Sage grouse data collection has become, and will continue to be, a high priority. Efforts from 1996 to 1998 exceeded that of previous years and will hopefully continue. Results from The Mesa Sage Grouse Study, as well as additional proposed research directed at oil & gas impacts to sage grouse in the Jonah Natural Gas Field, should improve our understanding of sage grouse ecology in the Upper Green River Basin. Likewise, the sage grouse study initiated in Jackson Hole in 1999 should provide valuable information on the status, population dynamics, mortality factors, and habitat use by this small and apparently isolated population. It is likely, however, that these investigations will highlight chick survival as a major driving force in the dynamics of local sage grouse populations, which will still beg the question, "how do we improve sage grouse chick survival?"
Jackson Hole Sage Grouse Study
See The Archives for past articles.
Copyright © 1999 The Sublette County Journal
All rights reserved. Reproduction by any means must have permission of the Publisher.
The Sublette County Journal, PO Box 3010, Pinedale, WY 82941 Phone 307-367-3713
Publisher/Editor: Rob Shaul email@example.com