Red-headed woodpecker (Melanerpes erythrocephalus) COSEWIC assessment and status report: chapter 7

Population Sizes and Trends

Search effort

The North American Breeding Bird Survey (BBS) is a large-scale survey that monitors population trends for birds in North America (Sauer et al. 2005). Surveys are conducted by volunteer birders at 50 three-minute stops at 0.8-km intervals along 39.4 km survey routes. At each stop, every bird seen or heard within a 400-m radius is recorded (Downes et al. 2005). This survey has proven to be a relatively effective means of monitoring Red-headed Woodpecker populations, because the majority of the survey routes are located in urban areas and their surroundings where this species is usually present (Sauer et al. 2005). Moreover, this species is highly vocal during the BBS survey period and can therefore be readily detected during the surveys (Cadman et al. 1987; Smith et al. 2000).

The Christmas Bird Count (CBC) is the largest and oldest program for monitoring winter bird populations in North America (i.e., 1900-2004, Sauer et al. 1996). In late December of each year, more than 40,000 volunteers record all species that they encounter within circles 24 km in diameter located throughout North America (Sauer et al. 1996). Although a summary of the data is available for 1900 to 2004 (National Audubon Society 2005), trend analyses are available only for 1958 to 1988 (Sauer et al. 1996). Trends are corrected for search effort by dividing the number of birds observed by the number of observer-party hours (Sauer et al. 1996). CBC data provide a measure of changes in abundance of wintering populations over time for this species.

The Ontario Breeding Bird Atlas project for 1981-1985 (Cadman et al. 1987) and 2001-2005 is an important source of data for estimating Red-headed Woodpecker population trends in this province. A comparison of the abundance index (i.e., the number of 10 km x 10 km squares per 100 km x 100 km block surveyed where the species was observed, divided by the total number of squares per block surveyed) of the two survey periods provides Red-headed Woodpecker population trends over a 20-year period. The methodology used in this project has proven effective for surveying this species because it is easily detectable by its call during the breeding season (Smith et al. 2000) and because it occurs mainly in agricultural areas in the southern part of the province, which was very well covered in both of the atlas surveys (Cadman et al. 1987).

In Quebec, the SOS-POP has surveyed birds at risk since 1994. This database is co-ordinated by the Association québécoise des groupes d’ornithologues (Quebec association of birdwatchers’ groups) and the Canadian Wildlife Service (CWS). Birds at risk are monitored chiefly by members of Quebec birdwatching clubs, who fill out observation sheets for each visit to determine species presence (F. Shaffer pers. comm. 2007).

The Canadian Migration Monitoring Network monitors populations of migrating passerines at monitoring stations across Canada (Environment Canada 2004). The main activities at these stations consist of banding birds and visually tracking migratory birds. The densities of migrating Red-headed Woodpeckers in Canada are probably too low for most stations to monitor this species effectively. There are currently nine monitoring stations in the Red-headed Woodpecker’s breeding range, one of which--Long Point Bird Observatory--has enough data to estimate long-term seasonal trends (Bird Studies Canada 2006).

Abundance

Rich et al. (2004) estimated the North American population of Red-headed Woodpeckers at approximately 2.5 million breeding individuals (i.e., 1.3 million breeding pairs). This estimate was derived from relative abundance counts on BBS routes, which were then converted to population estimates based on an estimate of an effective detection distance of 200m for Red-headed Woodpeckers. It was assumed that on average one member of a pair within detection distance was detected in each three-minute BBS count. There have been no new surveys to determine Red-headed Woodpecker abundance in Canada since the last status report on this species (Page 1996). The abundance estimates in the current report are based primarily on data derived from BBS trend estimates and on the knowledge of provincial experts and the results of various provincial atlas projects.

According to BBS-based population estimates, the total Canadian population in the 1990s was approximately 10,500 breeding pairs (P. Blancher unpubl. data), occurring primarily in Ontario and Manitoba. Assuming the Canadian population has declined by 48% since 1994, as suggested by BBS trend indices (see below), the current population of Red-headed Woodpeckers in Canada would be about 5,000 pairs.

Information from the recent Ontario Breeding Bird Atlas suggests a minimum of 500 pairs (based on presence/absence in 10 X 10 km squares; M. Cadman pers. comm. 2007) and a maximum of 1,900 pairs (based on extrapolations from atlas point counts; P. Blancher pers. comm. 2007) in Ontario. In Manitoba, the minimum population estimate is approximately 200 pairs (based on community knowledge; K. De Smet pers. comm. 2007; P. Taylor, pers. comm. 2007) and a maximum of 2,700 pairs (based on an estimate of 5,800 in the 1990s from BBS counts and a loss of about 53% since then (BBS trend indices); P. Blancher, pers. comm. 2007). There are an estimated 0-5 pairs occurring in Quebec (F. Shaffer, pers. comm. 2005). Together, these estimates suggest that the population of Red-headed Woodpeckers in Canada could range from a minimum of 700 pairs or 1,400 mature individuals to a maximum of 5,000 pairs or 10,000 individuals.

Density estimates for this species come primarily from the United States. In the southeastern United States, breeding densities of the Red-headed Woodpecker range from 2.3 pairs/40 ha ±0.43 (n = 16) to 24 pairs/40 ha (Kilham 1983; Hamel 1992 in Smith et al. 2000). Interestingly, in Illinois, 5 pairs/40 ha were reported in areas that had not been hit by severe outbreaks of Dutch elm disease and 24 to 63.8 pairs/40 ha following an outbreak in areas of high snag density (Kendeigh 1982).

In winter, densities range from 8.4 individuals/40 ha in upland forest (Graber and Graber 1979) to 34.2 individuals/40 ha in mature bottomland forest (Graber and Graber 1977 in Smith et al. 2000).

Fluctuations and trends

Historic and qualitative trends

North America

Red-headed Woodpecker populations have fluctuated widely since the first European settlers arrived in North America (Smith et al. 2000). The species was abundant in the 18th and 19th centuries, when it benefited from the large-scale clearing of the forests of the eastern and central United States (Smith et al. 2000). In the early 20th century, however, these populations declined continuously, because of the disappearance of the extensive mature forests dominated by oak and beech that had produced large quantities of acorns and beechnuts. Although Red-headed Woodpecker populations rose again throughout its range between the 1950s and the 1970s following the death of large numbers of elms and chestnuts from fungal diseases (Smith et al. 2000), they seem to have fallen again since 1980 (Page 1996). According to some authors, this decline is the result of the systematic felling of dead trees for firewood and the natural collapse of elm snags affected by Dutch elm disease in agricultural areas (Smith et al. 2000). In urban areas, the removal of dead trees and branches is believed to be an important factor in the loss of the species’ habitat (Smith et al. 2000).

Canada
Quebec

The Red-headed Woodpecker was probably more abundant in Quebec in the 19th century than in the late 1970s (Ouellet 1974). This species also seems to have been a regular breeder at certain sites on Montreal Island, such as Mount Royal, where it nested for a long period (i.e., 1936 to 1968) (Ouellet 1974). It occupied 29 sites from 1960 to 1996, compared with only 7 from 1997 to 2004 (SOS-POP, F. Shaffer pers. comm. 2005). There are no breeding records for Quebec in 2002 or 2003, which suggests that it is now only a sporadic breeder in this province (SOS-POP, F. Shaffer pers. comm. 2005).

Ontario

Although there are no historical data on Red-headed Woodpecker numbers in Ontario, this species was once regarded as relatively abundant in the southern parts of this province (Macoun and Macoun 1909; Taverner 1919). However, it began to decline in the early 1900s, and by the 1960s, its numbers had already declined to an alarming extent in many parts of its range where it was once common, such as North Bay, Lake Nipissing, Kingston, Point Pelee National Park (Peck and James 1983; Page 1996).

Manitoba

Although considered rare to uncommon in the 1800s, Red-headed Woodpecker populations increased rapidly in the early 1900s, peaking in about the 1960s (Manitoba Avian Research Committee 2003). In the 1980s, populations in this province appeared to decline and several local populations disappeared (P. Taylor pers. comm. 2005), while others have declined by at least 50% (Page 1996).

Saskatchewan

There are few historical data that could be used to identify a long-term trend for Saskatchewan. However, this species is believed to have been more abundant before the introduction of the European Starling (Smith 1996).

Recent and quantitative trends

North American Breeding Bird Survey

Long-term BBS data from the species’ North American breeding range indicate a significant decline of 2.6%/year in Red-headed Woodpecker populations between 1966 and 2005 (P £0.001, n = 1311 routes, Sauer et al. 2005). This corresponds to a population decline of 66% across North America since 1966. The decline is most pronounced in the northern and mid-western United States (Figure 3).

Figure 3. Percent change in Red-headed Woodpecker abundance in North America according to the Breeding Bird Survey (based on Sauer et al. 2005).

Figure 3.  Percent change in Red-headed Woodpecker abundance in North Americaaccording to the Breeding Bird Survey (based on Sauer et al. 2005).

In Canada, long-term BBS data show a significant decline of 3.4%/year (P<0.05, n = 69) for this species between 1968 and 2005, which amounts to a 70% decline in the population. Short-term BBS data show a non-significant decline of 0.70%/year (P>0.10, n = 36) between 1995 and 2005 (Figure 4; Downes et al. 2005). At the latter rate of decline, Red-headed Woodpecker populations in Canada would have decreased by about 7% in the most recent 10-year period.

Figure 4. Annual index of abundance for the Red-headed Woodpecker between 1968 and 2005 in Canada according to the Breeding Bird Survey (based on Downes et al. 2005)

Figure 4.  Annual index of abundance for the Red-headed Woodpecker between 1968 and 2005 in Canada according to the Breeding Bird Survey (based on Downes et al. 2005)
Christmas Bird Count

Abundance indices derived from CBC data for Red-headed Woodpeckers in Canada between 1960 and 2005 show a relatively stable, albeit fluctuating trend between 1960 and the mid-1980s, followed by a declining trend (Figure 5). For the period between 1958 and 1988, where trend analyses have been conducted, CBC data show a decline of 1.0%/year (n.s., n = 1107, Sauer et al. 1996) in North America as a whole and an increase of 0.3%/year (n.s., n = 41 Sauer et al. 1996) for Ontario, the only province with sufficient CBC survey circles to estimate a trend.

Ontario Breeding Bird Atlas

In Ontario, the percent of squares occupied by Red-headed Woodpeckers between the two atlas projects (i.e., 1980-1985 and 2000-2005) declined by 64% (A. Darwin unpubl. data), with severe declines in the Carolinian and Simcoe-Rideau Regions, the core breeding area in Ontario (effort adjusted: 47% fewer squares in the Carolinian Region, 30% fewer squares in the Simcoe-Rideau Region; L. Friesen pers. comm. 2007). The decline of the species in this province is also apparent from the comparison of the abundance indices for the two periods (i.e., the number of survey squares in which the species was observed fell in 33 of the survey blocks between atlas periods and rose in only 3; 2-tailed Wilcoxon signed rank sum test = -4.5, P £0.001) (C. Savignac, unpubl. data).

Figure 5. Red-headed Woodpecker population trends in Canadafor the period 1961-2005 according to the Christmas Bird Count (National Audubon Society 2005).

Figure 5.  Red-headed Woodpecker population trends in Canadafor the period 1961-2005 according to the Christmas Bird Count (National Audubon Society 2005).
Canadian Migration Monitoring Network

Between 1961 and 2004, Red-headed Woodpecker counts at Long Point Bird Observatory showed significant declines of 3.4%/year for the spring counts and 2.1%/year for the fall counts (Bird Studies Canada 2006).

Rescue effect

In Canada, the Red-headed Woodpecker is at the northern limit of its range and on the periphery of larger populations in bordering U.S. states, so an influx of individuals from these populations is possible. This hypothesis is supported by the relatively high frequency of individuals observed in fall and winter in several Canadian provinces where this species is not a breeder. Rescue from the U.S. is expected to be limited, however, becauseRed-headed Woodpecker populations in the U.S. have declined by 2.6%/year between 1966 and 2005 (see above), with 42.3% of states showing negative trends (Sauer et al. 2005).

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