Olive-sided flycatcher (Contopus cooperi) COSEWIC assessment and status report: chapter 7

Population Sizes and Trends

Search effort

The Olive-sided Flycatcher is conspicuous because of its loud song and tendency to perch on tall trees in open habitats. Despite this, there are few data on its ecology and abundance. Only three studies, in Alaska (Wright 1997), Oregon (Altman 1999) and Montana (Robertson and Hutto 2007) have specifically studied Olive-sided Flycatcher ecology. All other avian community surveys and breeding bird atlases conducted in Canada have documented this species in low numbers. Typically few individuals are recorded during point count surveys, and nests are hard to find, making breeding confirmation difficult.

Only the BBS and the checklist-based Étude des populations d’oiseaux du Québec (ÉPOQ, Association Québécoise des groupes d'ornithologues 2006) in Quebec have recorded the Olive-sided Flycatcher in sufficient numbers to describe population trends. Both monitoring programs do not account for habitat change that may occur at survey locations and do not have complete coverage of Olive-sided Flycatcher range either nationally (BBS) or within Quebec (ÉPOQ). Partners in Flight and the Canadian Wildlife Service have identified the inadequate coverage of BBS routes in the northern boreal part of the range of the Olive-sided Flycatcher as being a significant impediment to understanding national and regional population trends (Dunn 2005, Dunn et al. 2005). Altman and Sallabanks (2000) note, however, that the densest populations of Olive-sided Flycatchers are found in the western mountains from BC south to California, areas well-covered by the BBS. Wright (1997) found that the BBS survey protocol was well suited to detect the Olive-sided Flycatcher if singing males were present.

In Ontario, Ontario Breeding Bird Atlas data show a 7% decline in breeding range (measured by occupied atlas squares, adjusted for effort) between 1981-1985 and 2001-2005; this loss seems to be more serious in the southern parts of the species’ range (Birds Ontario, unpub. data). Because of the tendency to travel high in the canopy, this species is not well surveyed at migration monitoring stations. No Canadian migration monitoring stations have sufficient data to reliably assess population trends, although Thunder Cape Bird Observatory has found a negative (statistically non-significant) trend in spring captures and a positive (statistically non-significant) trend in autumn captures from 1995 to 2005 (Bird Studies Canada 2006).

Abundance

The Olive-sided Flycatcher is locally and patchily distributed and generally found at low densities throughout its range in Canada (0.05-3.49 birds per BBS route). In Canada, it reaches its highest densities in southern Yukon (3.49 birds per BBS route) and the coastal forests of British Columbia (2.39 birds per BBS route) (Sauer et al. 2005). Using estimates from BBS data, Rich et al. (2004) estimated the world population at 1.2 million individuals in the 1990s; this would have declined to about 700,000 in 2005 given known North American population trends. About 450,000 birds are estimated to breed in Canada (P. Blancher, unpublished data).

Fluctuations and trends

BBS data indicate widespread and statistically significant declines in Olive-sided Flycatcher populations across North America, with a significant 3.5% mean annual decline in North America (Sauer et al. 2005) for the period 1966 to 2005, and a 4% mean annual decline in Canada for the period 1968 to 2006 (Downes et al. 2007). The latter trend translates into a 79% decline over that 38-year period. These declines are strongest west of the Rockies where the highest breeding densities of Olive-sided Flycatchers are found (Altman and Sallabanks 2000).

The decline became steeper from 1985 to 1993, resulting in a more serious negative trend estimate for 1986 to 2006 (-5.3%), but has lessened since then (Table 1, Figure 2); the 10-year trend calculated from the 1996 to 2006 data is a significant annual decline of 3.3 %. The latter trend translates into a population decline of 29% over that decade.

Population trends at the provincial level are difficult to assess because of the smaller sample sizes in BBS data at that scale. Declining trends from BBS data from British Columbia, Ontario, Quebec and New Brunswick are statistically significant over the entire BBS survey period and the last 20 years (Table 1). In Quebec, these declines follow an increase in abundance from the mid-1970s to the mid-1980s which is described by both the BBS and the ÉPOQ (Figure 3). At Tembec’s Tree Farm Licence #14 in southeastern British Columbia, the Olive-sided Flycatcher population was also observed to be stable for the period 1999-2004 (Bayne 2005).

Table 1. Canadian Breeding Bird Survey trends for the Olive-sided Flycatcher (from Downes et al. 2007). Trend is presented as percentage change per year, with probability P (* = p<0.05, n = 0.05 < p < 0.1, no value = not significant), based on N survey routes. Provinces and territories with insufficient data to calculate trends are not shown.
Region 968-
2006
Trend
968-
2006
P
968-
2006
N
968-
1985
trends
Trend
968-
1985
trends
P
1968-
1985
trends
N
986-
2006
trends
Trend
986-
2006
trends
P
986-
2006
trends
N
1996-
2006
trends
Trend
996-
2006
trends
P
1996-
2006
trends
N
Canada
-4.0
*
468
-3.2
*
255
-5.3
*
394
-3.3
*
309
Yukon
 
 
 
 
-0.4
 
24
2.1
 
21
British Columbia
-5.7
*
110
-8.6
*
59
-5.2
*
103
-2.2
 
84
Alberta
2.3
 
67
17.7
n
23
-4.2
 
59
-12.7
 
47
Manitoba
-3.8
 
22
 
 
-3.0
 
20
2.6
 
18
Ontario
-9.5
*
70
-5.5
*
51
-13.2
*
47
-3.0
 
29
Quebec
-3.7
*
69
6.8
n
43
-11.2
*
48
-14.8
n
34
New Brunswick
-6.7
*
35
-6.1
n
27
-10.0
*
32
-11.7
n
24
Nova Scotia
-0.1
 
31
-0.5
 
24
-0.7
 
27
-2.7
 
24
Newfoundland and Labrador
-1.8
 
15
 
 
 
 
 
 

Figure 2.  Annual population indices for the Olive-sided Flycatcher in Canada, based on Breeding Bird Survey (BBS) data (1968-2006).

Figure 2.  Annual population indices for the Olive-sided Flycatcher in Canada, based on Breeding Bird Survey (BBS) data (1968-2006).

Figure 3.  Top: Annual population indices for the Olive-sided Flycatcher in Quebec, based on the mean number of birds observed per Étude des populations d'oiseaux du Québec (ÉPOQ) checklist. Only daily checklists produced between May 15 and July 13 in which observers stayed at least 30 minutes in the field, away from bird feeders were considered. Bottom: Breeding Bird Survey annual abundance indices for the Olive-sided Flycatcher in Quebec.

Figure 3.  Left: Annual population indices for the Olive-sided Flycatcher in Quebec, based on the mean number of

 

Table 2. United StatesBreeding Bird Survey trend results (from Sauer et al. 2005). Trend is presented as percentage change per year, with probability P, based on N survey routes.
Region 1966-
2004
trends
Trend
1966-
2004
trends
P
1966-
2004
trends
N
1966-
1979
trends
Trend
1966-
1979
trends
P
1966-
1979
trends
N
1980-
2004
trends
Trend
1980-
2004
trends
P
1980-
2004
trends
N
United States
-3.5
0.00
511
-2.5
0.04
201
-3.1
0.00
458
Alaska
-2.1
0.13
55
-2.3
0.10
55
Arizona
4.2
0.6
10
1.3
0.89
9
California
-3.9
0.00
115
-3.1
0.08
71
-4.0
0.00
105
Colorado
0.1
0.97
46
-3.0
0.77
4
0.3
0.85
45
Idaho
-3.1
0.08
20
-5.6
0.66
4
-3.4
0.07
19
Maine
-0.6
0.90
38
-3.6
0.63
13
-4.0
0.19
34
Michigan
-7.2
0.46
12
-10.2
0.34
2
-9.8
0.41
11
Minnesota
-2.5
0.51
26
1.0
0.91
10
-4.8
0.26
25
Montana
-2.4
0.09
19
0.4
0.97
5
-2.0
0.16
17
New Hampshire
-7.8
0.00
13
-0.4
0.90
10
-12.6
0.06
6
New Mexico
2.3
0.69
8
4.0
0.53
7
New York
-7.3
0.00
20
-10.3
0.04
16
-11.0
0.00
10
Oregon
-4.3
0.00
72
-4.2
0.03
28
-1.7
0.11
69
Utah
-4.9
0.29
18
-6.5
0.11
18
Vermont
-3.0
0.48
13
-7.1
0.17
9
0.3
0.98
9
Washington
-2.5
0.01
47
0.5
0.88
20
-3.7
0.00
45
Wisconsin
-0.3
0.85
19
4.7
0.12
6
0.4
0.85
16
Wyoming
-1.0
0.80
13
-1.5
0.72
13

Rescue effect

BBS results suggest Olive-sided Flycatcher populations in the United States are undergoing similar declines to those observed in Canada (Sauer et al. 2005, Table 2). The Olive-sided Flycatcher appears to use similar habitat in the United States and Canada, so immigrants would be adapted for conditions in Canada. The close proximity between US and Canadian populations would also mean that immigration is possible. However, similar declines in the relative abundance of the Olive-sided Flycatcher in the United States suggest that surplus individuals may not be available to immigrate to suitable, but vacant, habitat in Canada. Natural rescue of Canadian populations by populations in the United States is therefore possible, but very unlikely unless reasons for population declines in the United States can also be identified and addressed.

Page details

Date modified: