Unchecked deforestation throughout its Central and South American wintering grounds is the single greatest threat to the survival of this diminutive songbird.
by Tim Tiner
Deep within the largest stands of Ontario’s Carolinian forest, at the buggy bottoms of steep, hemlock-shrouded ravines and the inner reaches of tall-treed swamps, lies the domain of the Acadian flycatcher. Favouring prime pieces of one of the most diminished habitats in the country, the drab, olive-backed passerine is one of Canada’s rarest birds, though the riddle of its survival is proving to be more complex than was once thought.
Ranging throughout most of the eastern half of the United States and into Canada, Acadian flycatchers are decidedly misnamed, since their habitat reaches its northern limits largely in Ontario’s Carolinian zone rather than the Maritime provinces. They dwell between the understorey and lower canopy, launching from hunting perches to snatch beetles and caterpillars from the undersides of leaves or wasps and mosquitoes in midair. The lower forest is fairly open, usually only sparsely covered with saplings, witch-hazel or other understorey trees, in the lower branches of which this bird commonly nests.
The diminutive flycatcher frequents just a handful of large, wooded tracts in southern Ontario, particularly along central Lake Erie in the region’s two most forested counties: Norfolk, with 25 percent tree cover, and Elgin, with 16 percent. Most of its mature hardwood redoubts cover 40 hectares or more, enabling the shade-seeking bird to nest deeper than a hundred metres from the forest edge, often near or over creeks or other pools of water.
In 1994, the Acadian flycatcher was declared nationally endangered. It is also listed as endangered under Ontario’s Endangered Species Act. Since 1997, targeted surveys held every five years each tallied between 34 and 37 territorial males in Ontario. The birds’ sharp, distinctive “peet-sa” song, heard throughout the day and well into summer, makes them relatively easy to detect. The Acadian Flycatcher/Hooded Warbler Recovery Team, formed by the Canadian Wildlife Service (CWS) in 1996, speculates that while it is possible that 50 or more flycatcher pairs may nest in the province, an estimate of 27 to 35 pairs is more likely.
Although the surveys suggest that the Ontario population is stable, researchers are baffled by why it remains so tiny. Initially, in 2000, the recovery team set the goal of increasing the number of known nesting Acadians to 250 pairs, on the assumption that the birds, first noted in the province in 1884, must have been more common before European settlement. But after extensive studies, the team now believes some still poorly understood aspect of population dynamics, rather than habitat, is the main limiting factor.
Though most remaining Carolinian patches are smaller than three hectares, there are nevertheless some big tracts with no flycatchers, says Ministry of Natural Resources ecologist Dawn Burke, a member of the recovery team, who has studied the effects of forest management on the birds.
“They have dozens of woodlots to choose from,” she says, comparing Ontario’s cloistered Acadians to an eastern U.S. population of some two million that spreads into lower-quality forests. “Where they are less common, they tend to be in the best habitat.”
Lyle Friesen, a CWS songbird biologist and chair of the recovery team, concurs. “It may be just as valid to assume that the species was never common in the province, even when it was heavily forested, because the flycatcher was – and remains – primarily a southern species.”
In its draft recovery strategy in 2006, Friesen’s group changed its goal to 50 flycatcher pairs, holding that the Ontario population persists primarily due to periodic spillovers of first-time breeders from the United States seeking open nesting grounds. After a good breeding year in the south, explains Burke, more birds may head north.
Even in prime locations, Acadian flycatcher numbers ebb and flow, says biologist Dave Martin, who led surveys for the recovery team up to 2006. Once one pair settles, he notes, others tend to nest next to it, possibly attracted by opportunities for extra-pair matings, which are common among Acadians. But while successful nesters usually keep returning to the same sites, their offspring by instinct breed farther south, in the species’ core range. “Gradually, that little colony dies off. And then, 10 years later, you get a big influx of birds from the States and they recolonize,” says Martin.
Since the flycatchers prefer the largest and oldest forests, most occupy parks and other publicly owned lands in Ontario. The draft recovery strategy recommends managing as many of these properties as possible as mature-growth stands. Indeed, some conservation authorities have designated no-cut zones to help preserve species at risk. In 2002, the Long Point Region Conservation Authority set aside almost 850 hectares as Natural Heritage Woodlands. On the other hand, the recovery team has come up against logging in Middlesex County-owned forests in the Skunk’s Misery complex, a traditional stronghold of the endangered flycatchers, southwest of London.
The birds seem to be expanding their range slightly; scattered sightings at the northern limits of the Carolinian zone and beyond have been charted in the most recent breeding bird atlas. Because Acadians are persistent nesters – making at least three attempts if their first nests fail and occasionally raising a second brood into August – researchers speculate that global warming could accelerate their spread north. “With a one or two degree increase in temperature, there could be a thousand flycatchers in Ontario,” says Martin.
But trouble in the Acadian flycatcher’s winter home, stretching from lower Central America to the western reaches of Venezuela, Columbia and Ecuador, could lead to a different future. “All of our Acadian flycatchers cram into this tiny space on their wintering grounds where deforestation is racing ahead unchecked,” says York University biology professor Bridget Stutchbury, who studies songbird migrants in Ontario and the tropics. “They have lost a huge amount of winter habitat.” As the rainforest disappears, she notes, migrant birds forced into scrub suffer higher mortality, are in poorer condition to migrate and often do not fly north on time.
The birds’ fate, says Stutchbury, largely rests on efforts to preserve the remaining rainforest and promote sustainable, shade-grown coffee plantations, which readily support Acadian flycatchers and other migrants. “The biggest race against time is on their wintering grounds.”
Tim Tiner is the author of several nature guidebooks and a long-time contributor to ON Nature.