BIRDS
Daniel F. Brunton
RECENT TRENDS
A dramatic decline is the widely accepted interpretation of the overall trend in woodland bird numbers in this ecozone over the last 20 to 30 years or so, accompanied by a general increase in waterfowl. Particularly dramatic aspects of these trends are noted below:
- decline in passerine populations - the "Silent Spring" condition predicted by Carson (1962) is now evident in many woodland passerine populations in the Mixedwood Plains Ecozone, particularly with species which winter in tropical America (Bradstreet 1994).
Case Study: Where have all the migrants gone?
Time was, not that long ago in the lives of many active birders, when the spring days were marked by a slow rise in the hordes of migrant perching birds racing northward for another year's nesting. The peak could be predicted as numbers grew and grew until one day the trees, the sky, the shrubs... even lawns... across the Mixedwood Plains Ecozone would be, as the saying goes "dripping with birds". No more. The steady decline in such populations has been well documented since the 1970s. Long-term base line data necessary to quantify these declines, however are lacking. We didn't start looking really carefully until the 'cows' were out of the 'barn'! Sadly, though, the general picture is clear.
Open country, native scrub and old growth forest species seem to have been particularly hard hit. Predictably, these habitats are amongst those most intensively altered locally and internationally in recent decades. The numbers of common species like White-throated Sparrow, Savannah Sparrow, Brown Thrasher and Vesper Sparrow passing through major migration points along the Great Lakes have declined by over 40% in the last 30 years. Species which thrive in disturbed landscapes in the Mixedwood Plains Ecozone and the Boreal Forest (American Robin, Chipping Sparrow, Yellow-rumped Warbler, etc.) demonstrate a comparable or greater increase (up to 330%) in the same period (Francis and McCracken 1996). The overall impact, however, is a dramatic, ominous quietness in many woodlands across the Mixedwood Plains Ecozone.
- selective population enhancement - a huge increase in bird feeding since the 1950s has encouraged a significant expansion of population and range for a number of formerly marginal or absent species, including Northern Cardinal, Mourning Dove and House Finch. As many as one in every four homes may maintain feeding stations through at least the winter season in the ecozone.
Case Study: Northern Cardinal
Before substantial alteration of the hardwood forests of eastern North America, the Northern Cardinal did not extend as a breeding species north of Massachusetts and southern New York (Nuttall 1832) and was only recorded in Canada just before 1850. By 1902 it was breeding along Lake Erie. It had reached western Lake Ontario by the 1920s and the northern edge of the Mixedwood Plains Ecozone by the early 1940s. It was an established breeding species in the Montreal - Ottawa area by the mid-1970s and now breeds throughout the ecozone (Godfrey 1986; Dow 1994). It appears that cardinals spread northward and eastward along rivershores; the highest population densities in the ecozone remain along such migratory corridors. Severe snowfall conditions present a major detriment to these pioneering populations, however. It is expected that without the critical support provided by feeding stations, winter mortality would have eliminated the possibility of a sustainable population level becoming established (Dow 1994).
- increased scavenger populations - the proliferation of large landfills has contributed significantly to increased populations of scavengers including several gull species (Fig. B-4), Common Crow, and European Starling, particularly close to the shores of the Great Lake and the St. Lawrence and Ottawa Rivers.
Case Study: European Starling
The introduced European Starling is closely associated with human-altered landscapes, particularly those in which urban and agricultural areas in which substantial amounts of waste vegetable and animal matter are available for food. It is now one of the most common species in North America and competes aggressively for nesting sites in artificial and natural cavity sites, negatively affecting natural populations of native species such as Red-headed Woodpecker, Eastern Bluebird and Tree Swallow. It was first reported breeding in the Mixedwood Plains Ecozone in the Ottawa Valley and along the northern shore of Lake Ontario in 1922 and was abundant throughout by the 1930s. It is suspected that Starling breeding populations had stabilized in substantial portions of the ecozone by the 1950s (Bowman 1987) but it appears that at least wintering populations have increased dramatically in urban areas since that time in response to increased food availability at landfills, fast-food restaurants and the like.
- waterfowl breeding range changes - a proliferation of sewage lagoons has encouraged expanded breeding range of various waterfowl species, including Ruddy Duck, Redhead and Wilson's Phalarope (Cadman et al. 1987, Austen et al. 1994).
Case Study: Wilson's Phalarope
This shorebird is characteristic of shallow, marshy prairie sloughs in central and western North America. Prior to the 1950s it was a rare to uncommon breeder across the Carolinian Zone. Expansion eastward progressed rapidly thereafter with breeding being noted at Montreal by 1974. The species was well established in the lower Ottawa Valley by 1985 (Cadman 1987). The majority of such nestings occur at sewage lagoons Austen et al. (1994). These water bodies have a strong structural similarity to natural breeding habitat and have greatly facilitated the species' spread across the Mixedwood Plains Ecozone.
- competitive introductions - the intentional introduction and rapid population increase of Canada Goose and (locally) Mute Swan have negatively affected local waterfowl populations along Great Lakes and along the St. Lawrence and Ottawa River systems.
Case Study: Canada Goose
Although a once naturally occurring if uncommon species in the Mixedwood Plains Ecozone, the Canada Goose (Fig. B-5) was extirpated by habitat alteration and over-hunting during the agricultural and industrial development of the area (Lumsden 1987). Hatchery-raised geese were released widely in the area after the 1930s, with particularly heavy introduction programs being undertaken after 1960. The genetic constitution of these populations varies considerably, with strains of several subspecies being involved. Accordingly, the hordes of geese now dominating sections of the Lake Ontario and St. Lawrence River shores and becoming increasingly common along the Ottawa River and elsewhere do not constitute a natural populations. These aggressive animals are detrimental to other waterfowl species and constitute a growing control problem.
- fragmentation of Carolinian Zone habitat - reduction of woodland size and number has resulted in a significant reduction in rare bird populations such as Acadian Flycatcher, Louisiana Waterthrush, Prothonotary Warbler and Cerulean Warbler (Allen et al. 1990).
Case Study: Acadian Flycatcher
The Acadian Flycatcher has always been considered a rare breeding species in the Carolinian Zone of the Mixedwood Plains Ecozone (Woodliffe 1987). It is an area-sensitive species and inhabitants large, low, mature deciduous forest sites, rarely prospering in woodlands less than 35 ha in size (Austen et al. 1994). Fragmentation of remaining Carolinian Forests has resulted in a significant population decline in this area (as it has in New York state as well). The Acadian Flycatcher was designated Endangered in Canada by COSEWIC in 1995.
- increased colonial waterfowl - reduction in toxicity of Great Lakes water and reduced persecution has resulted in a large increase and spread of gulls, Double-crested Cormorants and other colonial waterfowl (Blokpoel 1994).
Case Study: Double-crested Cormorant
Colonial waterbirds have been severely impacted in historic times by human predation and environmental contamination. One of these species, the Double-crested Cormorant, spread into the Mixedwood Plains Ecozone as a breeding species from the northwest and was common on the Great Lakes by the early 1950s. Human predation and (most significantly) environmental pollution substantially reduced populations ofthis and several other waterfowl. With improved water quality and protection from harassment, however, population figures increased rapidly after 1975 (Weseloh 1987). They are now well established along the Great Lakes - St. Lawrence shores and are breeding along the Ottawa River. While populations of several colonial waterfowl in this area have increased by 10-20% since the late 1970s, Double-crested Cormorants numbers have increased by over 40% in the same period (Blokpoel 1992).