Committee on the Status of Species at Risk in Ontario (COSSARO) Assessed June 2010 by COSSARO as Endangered

June 2010


Part 1: COSSARO Candidate Species at Risk evaluation form – June 2010

Acadian Flycatcher (Empidonax virescens)

Current designations:

GRANKG5 (02 Dec.1996)
NRANK Canada – N2B (27 Sep. 2000)
COSEWIC -- Designated Endangered (April 1994). Status re-examined and confirmed in November 2000 and April 2010.
SARA – Endangered, Schedule 1
General Status Canada – At Risk (2005)
ESA 2007 – Endangered
General Status Ontario – At Risk (2005)

Distribution and status outside Ontario:

The northern limit of the breeding range of Acadian flycatchers extends from southeastern South Dakota eastwards across the southern Great Lakes through southwestern Ontario to southern New England. The southern limit of the breeding range starts in eastern Texas through the Gulf coast to northern Florida. This neotropical migrant winters in Nicaragua, Costa Rica and Panama and northwestern South America (Whitehead and Taylor 2002; COSEWIC 2010; NatureServe 2010).

Eligibility criteria

Native status

Yes. This species has been known from Ontario for well over a century, with the first nesting records dating from1884 and 1910 (Saunders 1909, 1910 in COSEWIC 2010).

Taxonomic distinctness

Yes. This bird is best distinguished from the other 14 species of flycatchers in the genus by its distinctive peet-sa song, other characteristic vocalizations, and habitat (COSEWIC 2010). There is no documented dispute concerning the taxonomic status of this species and there is only one subspecies in Canada (COSEWIC 2010).

Designatable units

In Ontario, Acadian Flycatchers breed in the Carolinean ecoregion of southwestern Ontario (COSEWIC 2010). No subspecies are recognized and no geographic variation is known, therefore there is only one designatable unit in Canada and Ontario.

Priority-setting criteria

Recent arrival



No. This species has been known to breed in Ontario for well over a century.

Primary criteria (rarity and declines)

1. Global rank

Not in any category. G5.

2. Global decline

Not in any category. Most declines of this species occurred during the period of extensive deforestation in eastern North America in the late 1800s (Martin 2007), with some recovery having occurred simultaneous with forest recovery in the latter part of the 20th century (Whitehead and Taylor 2002). During the period 1966-2007, the continental trend for North America Breeding Bird survey was -0.1%/yr (p=0.61, n=973), indicating Acadian Flycatchers have remained relatively stable across its North American range over the past 40 years. Similarly, over the past 10 years (1997-2007) the continental trend for the past shows a non-significant decline of 0.45%/yr (p=0.33, n=717; Sauer et al. 2008).

3. Northeastern north america ranks

Not in any category. Acadian Flycatchers breed in 18 northeastern jurisdictions. Rhode Island is the only one apart from Ontario (S2S3B) that has an S1 or S2 ranking (S1). This bird is considered common and not of conservation concern in most other jurisdictions within its breeding ranges in the United States but is ranked as Vulnerable (S3) in all states bordering Ontario other than Pennsylvania and Ohio (NatureServe 2010).

4. Northeastern north america decline

Not in any category. Although unquantified, extensive range contraction is presumed to have occurred in northeastern United States during the 1900s. Beginning in the 1960s, Acadian Flycatchers began to reoccupy parts of their range, likely facilitated by maturation of second growth forests (Whitehead and Taylor 2002). In northern New England, in particular, since the 1980s breeding records have indicated an expansion of the historic breeding range and stable or slightly increasing population trends (Whitehead and Taylor 2002; Sauer et al. 2008). While BBS long-term trends for Ohio and Pennsylvania over the 1966-2007 period indicate significant declines of 2.3%/yr (p=0.04, n=53), and 0.4%/yr (p=0.28, n=78), respectively, these trends reversed somewhat during the most recent 10-year period (1997-2007; Sauer et al. 2008).

5. Ontario occurrences

Special Concern. 32 extant occurrences (NHIC 2010). In Ontario, only 30-50% of the known breeding sites may be occupied by Acadian Flycatchers in any given year. Birds may utilize a suite of breeding sites in some years, but then shift to other sites in subsequent years (McCracken et al. 1998 in COSEWIC 2010). Although this species was considered to be a rare but regular breeder along the north shore of Lake Erie prior to the 1970s, new breeding locations began to be discovered due to increased atlas coverage and more targeted surveys (COSEWIC 2010). The number of sites occupied in any given year appears to have been fairly stable even as the total number of known sites has gradually increased over time. The Acadian Flycatcher/Hooded Warbler Recovery Team estimates the Ontario population to be between 27-35 pairs in any given year (Martin 2007). In its most recent status report, COSEWIC (2010) estimated the total Canadian population in 2007 to be 112 adults (48 pairs and 16 single males), all of which are found in Ontario during the breeding season.

6. Ontario decline

Not in any category. The Acadian Flycatcher’s historic distribution in Ontario (prior to the late 1800s) is not well known, as the southern Ontario landscape was by that time already radically altered by the conversion of the extensive woodlands and wetlands to agricultural cropland and pasture at the time of the first nesting records (COSEWIC 2010). The limited available evidence suggests, however, that this bird was never very common north of the Great Lakes, even though their known preferred habitat was much more extensive in southern Ontario at one time. Early records of naturalists provide no indication that Acadian Flycatchers ever existed in other than a small population in Ontario (J. McCracken, pers. comm.).

In more recent decades, this species has been surveyed through the Ontario Breeding Bid Atlas, Forest Bird Monitoring Program (FBMP) routes in Ontario, Ontario Rare Breeding Bird Program (ORBBP), the Ontario Birds at Risk (OBAR) program, and surveys of Carolinian forest birds, and surveys undertaken by the Acadian Flycatcher/Hooded Warbler Recovery Team (COSEWIC 2010). Available information suggests that the Acadian Flycatcher population in Ontario has been relatively stable over the past decade; the Ontario Breeding Bird Atlas results also suggest a stable or increasing population over the past two decades (Martin 2007). Accurate determination of a trend one way or another may be further complicated because the population is small, territorial birds may be hard to detect, and irregular influxes of birds into previously unoccupied habitat may lead to substantial fluctuations in the population in certain years (Heagy et al. 1997 in COSEWIC 2010).

7. Ontario’s conservation responsibility

Not in any category. The current distribution of Acadian Flycatchers in Ontario represents approximately 1% of the total global breeding range.

Secondary criteria (threats and vulnerability)

1. Population sustainability

Endangered. With a total population of not more than 50 pairs scattered across a relatively large area (ca. 35,000 km2, there is good reason to believe the Acadian Flycatcher in Canada may not be self-sustaining. Its relatively stable status over recent decades may well be reliant on a constant influx of individuals from neighbouring populations in the United States (especially Ohio and Pennsylvania). A preliminary population and habitat viability analysis for the Acadian Flycatcher in Ontario suggested that the Canadian population is not self-sustaining, predicting a 93% risk of extirpation after 100 years, given a starting population size of 30 breeding pairs and no immigration (Tischendorf 2003 cited in COSEWIC 2010). Simulation models suggested that one immigrating breeding female every 2 years may be sufficient to eliminate the extinction risk. It is important to note that average observed pairing success rates in Ontario are considerably lower (70% average at core sites) than observed in areas of higher population densities (91% average over 4 years in a Pennsylvania study area;

Woolfenden et al. 2005), and that overall low habitat quality in Ontario (due to forest fragmentation and prevalence of edge habitats) leads to reduced seasonal productivity, further compromising population viability (COSEWIC 2010).

2. Lack of regulatory protection for exploited wild populations

Not in any category. The Acadian Flycatcher is protected in Canada under the Migratory Birds Convention Act.

3. Direct threats

Endangered. Because Acadian Flycatchers most commonly nest in large blocks of mature, closed-canopy forest habitats, they are sensitive to forest fragmentation effects. Forest cover within the breeding range of this species in Ontario has not exhibited similar recovery trends to those in Northern New England over recent decades. In the agriculture-dominated landscapes of southwestern Ontario, forests remain highly fragmented: two-thirds of all forest patches are less than 5 ha and only a few hundred patches are more than 100 ha in size (Flaxman 2004 in COSEWIC 2010). Due to high fragmentation, less than 2% of the Carolinian region consists of forests >100 m from edge, and less than 0.5% are >200 m from edge (Cadman 1999). Nest predation is the most common cause of nest failure, with highest success in the interior of large mature forest more than 600 m from the nearest edge. In Ontario, however, this species also nests in narrower ravine habitat of mature forest, suggesting that edge effects in such a context may pose less of a concern than elsewhere in the range. Forestry practices that remove large trees can negatively affect this species, which exhibits high nest fidelity. About half of the known Acadian Flycatcher sites in Ontario are on publicly-owned lands, but most of these sites are working forests that are being actively managed for timber and fuelwood production (COSEWIC 2010).

An important threat that appears imminent is the spread of exotic forest pests and pathogens into Acadian Flycatcher habitats in Ontario. Several of this bird’s preferred nest tree species are being decimated by the Hemlock Wooly Adelgid, (Adelges tsugae) in particular (Allen et al. 2009), which already occupies almost half of the range of hemlock in northeastern United States, is spreading northward at an annual rate of ~20 km, with current infestations about 200 km from Ontario (Allen et al. 2009). If these spread into southern Ontario (as predicted), it will bring devastating consequences to Acadian flycatchers that nest in hemlock trees in ravine habitats (COSEWIC 2010). As mentioned above, Acadian Flycatchers in Ontario are further threatened by their small population size.

It is quite plausible, therefore, that more than 75% of the documented occurrences in the province may be directly affected by all or some of the threats listed above.

4. Specialized life history or habitat-use characteristics

Threatened. Acadian Flycatchers are habitat specialists, nesting in mature closed- canopy forests with an open understorey. In Ontario, this species is typically found either in large patches of mature deciduous forest or in mature, forested ravine settings, and has a demonstrated susceptibility to forest loss, fragmentation, and degradation.

COSSARO criteria met (primary/secondary)

Endangered – [0/2]
Threatened – [0/1]
Special concern – [1/0]
Meets Endangered under COSEWIC criteria (see last page)


The Acadian Flycatcher (Empidonax virescens) is a small, olive-green medium- to long- distance neotropical migrant songbird. In Canada, the breeding range of this species is restricted to southwestern Ontario where it is typically found either in large patches of mature deciduous forest or in mature, forested ravine settings. Although the preferred habitat of these birds has diminished by as much as 90 per cent since European settlement, there is no indication that this species has existed in Ontario in other than a small population. Within the range core south of the Great Lakes, Acadian Flycatchers have existed at stable population levels over the past several decades, with some increasing trends in New England states. Likewise, the Ontario population appears to have been relatively stable over the past 10-20 years. Nevertheless, it is a small population of no more than 35-50 pairs, which is very likely not sustainable except through immigration from U.S. populations. In the agriculture-dominated landscapes of southwestern Ontario, forests remain highly fragmented. Forest pests that are removing preferred nest trees are increasing in northeastern United States, and threaten to enter Canada, imposing imminent threats to Acadian Flycatcher nesting habitat. Because of the small current population size and habitat threats, this species is designated as Endangered in Ontario.

Information sources

Allen, M.C., J. Sheehan, Jr., T.L. Master, and R.S. Mulvihill. 2009. Responses of Acadian Flycatchers (Empidonax virescens) to hemlock wooly adelgid (Adelges tsugae) infestation in Appalachian riparian forests. Auk 126:543- 1302 553.

Cadman, M. 1999. Conserving what’s left of southern Ontario’s forest birds. Pp. 24-28 in Kettle, A. (compiler). 1999. Southern Ontario Woodlands: the conservation challenge. Conference Casebook. Federation of Ontario Naturalists, Don Mills, ON. 164 pp.

COSEWIC. 2010. COSEWIC Status Report on Acadian Flycatcher Empidonax virescens. Committee on the Status of Endangered Wildlife in Canada, Ottawa. Two-month Interim Report (Feb. 2010). 37 pp.

Martin, D. 2007. Acadian Flycatcher, pp.334-345 In Cadman, M.D., D.A. Sutherland, G.G. Beck, D. Lepage, and A.R. Couturier (eds.). 2007. Atlas of the Breeding Birds of Ontario, 2001-2005. Bird Studies Canada, Environment Canada, Ontario Field Ornithologists, Ontario Ministry of Natural Resources, and Ontario Nature, Toronto. 706 pp.

NatureServe. 2010. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia. (Accessed: May 20 2010).

Natural Heritage Information Center (NHIC). 2010. Empidonax virescens General Element Report in NHIC Elements Database. [accessed May 20, 2010].

Sauer, J. R., J. E. Hines, and J. Fallon. 2008. The North American Breeding Bird Survey, Results and Analysis 1966 - 2007. Version 5.15.2008. USGS Patuxent Wildlife Research Center, Laurel, MD

Whitehead, D.R. and T. Taylor. 2002. Acadian Flycatcher (Empidonax virescens). In The Birds of North America Online (A. Poole, ed.). Cornell Lab of Ornithology, Ithaca, NY.

Woolfenden, B.E., B.M. Stutchbury, and E.S. Morton. 2005. Male Acadian Flycatchers, Empidonax virescens, obtain extra-pair fertilizations with distant females. Animal Behaviour 69:921-929.

Appendix 1: Northeastern North America Rank, Status And Decline

LBNot present
MANot present
MBNot present
MENot present
NBNot present
NFNot present
NHNot present
NSNot present
PENot present
QCNot present
VTNot present

Occurs as a native species in 18 of 29 northeastern jurisdictions Srank or equivalent information available for 18 of 18 jurisdictions = 100% S1, S2, SH, or SX in 2 of 18 = 11.1%

Part 2: Ontario Evaluation Using COSEWIC Criteria

Regional (Ontario) COSEWIC Criteria Assessment

Criterion A – Declining population

No. Ontario population has been stable since the early 1980s.

Criterion B – Small distribution and decline or fluctuation

No. Does not meet criterion. EO is >20,000 km². IAO is <500 km², but there is no evidence for decline, fragmentation or any extreme fluctuation in populations, habitat or range.

Criterion C – Small population size and decline

No. Although population size is <2500 mature individuals, there is no evidence of any decline or extreme fluctuation in numbers.

Criterion D – Very small or restricted

Yes. Endangered. Meets D1; population size is <250 mature individuals.

Criterion E – Quantitative analysis

Yes. Threatened. A preliminary analysis predicted a 93% risk of extirpation after 100 years, given a starting population size of 30 breeding pairs and no immigration.

Rescue effect

Yes. Populations are relatively secure in adjacent U.S. states, although increasing concerns about forest pathogens in the Northeast may affect this in the future.