Greater sage-grouse (Centrocercus urophasianus) COSEWIC assessment and status report: chapter 7

Population Sizes and Trends

Search effort

Greater Sage-Grouse population trends and status are based largely on monitoring males on leks. Concerns have been raised regarding the validity of using lek counts as population indices (Walsh et al. 2004, Strohm 2005). Attendance varies daily, seasonally and annually (Walsh et al. 2004). Indices derived from lek counts are not corroborated in models with realistic demographic rates (Strohm 2005), and variable search effort may misrepresent population trends (Aldridge 2000, Aldridge and Brigham 2003). Lek counts were not performed on an annual basis in Alberta and Saskatchewan until the last decade (Table 1, table2) (See Distribution: Canadian Range for more information).

In Alberta,each lek receives a single count annually at the end of April over a 3-day period. Surveyors arrive at each lek 1 hour prior to sunrise and remain until after sunrise or the birds fly away for the day. Up to 2 hours can be spent at each active lek (Eslinger pers. comm. 2006). Monitoring of leks was sporadic from 1968-1996. From 1997 onward, lek counts were conducted annually at all occupied and previously occupied leks (Alberta Fish and Wildlife Division, Alberta Sustainable Resource Development 2006).

In Saskatchewan, monitoring has been undertaken by Saskatchewan Environment and Resource Management biologists (1987-1994) in collaboration with Grasslands National Park (1996-2006) (Wynn 1996). In Grasslands National Park prior to 1994, leks were enumerated 3 times each spring. From 1995-2006, leks were monitored 4 times on specified count days (Wynn 1996). On count days, observers arrive at each lek ½ hour prior to sunrise and remain for 2 hours. Unoccupied leks have not been monitored on an annual basis (Grasslands National Park of Canada 2006). Survey of the leks in southwest Saskatchewan is in accordance with protocol recommended by the Western States Sage-Grouse Technical Committee (McAdam pers. comm. 2006). Lek counts are conducted every 7-10 days between early April to early May and at least one lek count coincides with the day Alberta counts are done (McAdams pers. comm. 2006).

Abundance

Surveys in spring 2006 enumerated 90 males at 9 leks in Alberta, and 60 males on 6 leks in Saskatchewan, for a cumulative average of 10 males/lek in both provinces (Tables 2, table3). Population estimates reported previously in Canada use a low and high estimate (Aldridge and Brigham 2003). The low estimate uses the high count of males on leks and assumes a sex ratio of 2 females: 1 male (Aldridge and Brigham 2003; Lungle 2006). A second, high estimate includes the 2:1 sex ratio, but also assumes only 90% of leks were counted and 75% of males were counted on leks. Using these assumptions, the Canadian estimate in 2006 is 450-667 birds. Population estimates are 270-400 in Alberta, and 180-267 in Saskatchewan.

Fluctuations and trends

Annual rates of change suggest long-term declines of 2%/year in Greater Sage-Grouse across western North America (Connelly et al. 2004). Greater Sage-Grouse populations in Canada appear to be cyclic (Table 1, table2); however, inconsistent monitoring between years and provinces make it difficult to assess these cycles and annual rates of change (Aldridge 2000; Connelly et al. 2004). The overwhelming trend appears to be one of decline. In Alberta, the number of individuals may have declined by as much as 85% since 1968 and 34% in the past decade. Aldridge and Brigham (2003) and Connelly et al. (2004) calculated similar rates of population decline (66-92%: 1968-2002 and 80%: 1975-2003). Connelly et al.(2004) report the number of individuals in Saskatchewan has declined 28-51% in the past decade (1996-2006); since 1988, the Saskatchewan population has declined 90-94%. Similarly, declines of 60-90% were reported prior to 1994 (Aldridge and Brigham 2003; McAdam 2003, Connelly et al. 2004). Routine monitoring was only initiated in 1994 (Aldridge and Brigham 2003) making assessment of long-term population trends impossible (Connelly et al.2004).

Using the lower population estimates, the number of individuals in both provinces has declined from 777 in 1996 to 450 in 2006, a 42% decline. From 1988 to 2006 the total Canadian population declined 88%. Similar results are shown for leks, which declined in number from 30 to 15 from 1996 to 2006 (50% decline, Table 3). Of 21 leks monitored in Alberta in 1968, 17 (81%) had been abandoned by 2006 (Alberta Fish and Wildlife Division, Alberta Sustainable Resource Development 2006). In Saskatchewan lek abandonment rates appear even greater. Of 61 leks occupied in 1988, 54 (89%) had been abandoned by 2005 (Grasslands National Park of Canada 2006). However, it appears that 22 (36%) leks occupied in 1988 were not monitored in subsequent years, and 4 (7%) did not have > 2 males during the assessment period or within 5 years of that period.

Table 1. Summary of Greater Sage-Grouse surveys in Alberta and population estimates 1968-2006 (Data provided by Alberta Fish and Wildlife Division, Alberta Sustainable Resource Development 2006)
Year Number of Active LeksTable notea Number of Males Number of Males/Lek Spring Population Estimate (Low) Spring Population Estimate (High)
1968
21
613
29.2
1839
2724
1969
20
554
27.7
1662
2462
1975
19
212
11.2
636
942
1976
19
347
18.3
1041
1542
1977
13
286
22.0
858
1271
1978
13
235
18.1
705
1044
1979
11
198
18.0
594
880
1980
16
482
30.1
1446
2142
1981
16
524
32.8
1572
2329
1983
18 (1)
358
19.9
1074
1591
1985
14
208
14.9
624
924
1987
13
400
30.8
1200
1777
1989
12
344
28.7
1032
1529
1991
11
241
21.9
723
1071
1994
8
70
8.8
210
311
1995
12 (1)
110
9.2
330
489
1996
11 (2)
136
12.4
408
604
1997
8 (1)
122
15.3
366
542
1998
8
124
15.5
372
551
1999
9
117
13.0
351
520
2000
8
126
15.8
378
560
2001
9
114
12.7
342
507
2002
10 (2)
89
8.9
267
395
2003
9
94
10.4
282
418
2004
9
94
10.4
282
418
2005
9 (1)
95
10.6
285
422
2006
9 (1)
90
10.0
270
400

 

Table 2. Summary of Greater Sage-Grouse surveys in Saskatchewanand population estimates 1988-2006
(Data provided by Grasslands National Park of Canada)
Year Number of Occupied Lekstable noteb Number of Males Number of Males/Lek Spring Population Estimate (Low) Spring Population Estimate (High)
1988
61 (4)
934
15.3
2802
4150
1994
15 (1)
93
6.2
279
413
1995
16 (1)
105
6.6
315
467
1996
19 (2)
123
6.5
369
547
1997
10
61
6.1
183
271
1998
11
122
11.1
366
542
1999
8
101
12.6
303
449
2000
10
126
12.6
378
560
2001
10
106
10.6
318
471
2002
10
84
8.4
252
373
2003
10
81
8.1
243
360
2004
8
60
7.5
180
267
2005
8
62
7.8
186
276
2006
6
60
10.0
180
267

 

Table 3. Lek abandonment in Albertaand Saskatchewan 1996-2006. Leks in parenthesis are those consisting of < 2 males within the assessment period or within 5 years.
Location Occupied Leks 1996 Occupied Leks 2006 Abandonment Rate
Saskatchewan
19 (2)
6 (0)
68%
Alberta
11 (2)
9 (1)
18%
Total
30 (4)
15 (1)
50%

Rescue effect

Vast tracts of sagebrush have been removed in northeastern Montana, effectively isolating the Alberta population (ASGRAG 2005, Carlson pers. comm. 2006). Movement of grouse between Alberta and eastern Montana is unlikely due to conversion of native rangeland (Carlson pers. comm. 2006). However, there appears to be an essential corridor for gene flow in western Saskatchewan that connects Alberta to the rest of the population and evidence exists of long-range dispersal events (> 200 km) between Alberta and Montana (Bush pers. comm. 2006). On going research at the University of Montana is hoping to elucidate the amount of cross-border movement of radio-marked Greater Sage-Grouse (Tack pers. comm. 2006).

Lek counts of Greater Sage-Grouse north of the Milk River in the USA suggest declines in Greater Sage-Grouse in the past decade mirroring the Canadian population trends (Carlson pers. comm. 2006). North of the Milk River, the habitat is mixed prairie-grassland with silver sagebrush dominating, whereas south of the river the community is a mixture of silver and big sagebrush (Carlson pers. comm. 2006). In regions south of the Milk River such as south Phillips and Valley Counties, the grouse population appears large and stable (Carlson pers. comm. 2006).

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