A land manager's guide to conserving habitat for forest birds in ...

Garlic mustard — Photo: Robert McCaw
Prothonotary Warbler — Photo: Greg Lavaty
House Wren — Photo: Jeff Nadler
facilitated the gradual replacement of trees which do not tolerate
shade, or can moderately tolerate shade (shade intolerant and
mid-tolerant tree species like birch and pine) with trees that can
tolerate shade (shade tolerant tree species like sugar maple and
American beech). Exotic diseases (such as chestnut blight and
Dutch elm disease), invasive plants (like garlic mustard and
European buckthorn), and exotic insects (such as gypsy moth
and emerald ash borer) shape the forests of southern Ontario.
Even the white-tailed deer, by foraging heavily on woodland trees
and shrubs has, and continues to change the structure of
woodlands today.
These historical and current driving forces have had a large
effect on the nature of the forests that remain on the landscape, and
hence the wildlife that depend on these forests for habitat, including
forest birds. Birds are important components of biodiversity, the
health of their populations serve as a benchmark of the health of
our ecosystems (see The Value of Biodiversity page 7). Biodiversity is
the variety of plants, animals, and other living organisms in all
their forms, from the gene and species level up to the ecosystem
level. Though forest dependent birds likely suffered declines with
the initial transformation of the landscape by Europeans in the
18th and 19th centuries, it was not until the late 1930s that
methods were developed to properly count bird populations and
allow trends to be documented (see How do we measure bird
populations trends page 9). It is known that since the 1960s
population declines have occurred in many forest bird species.
Today many of these continue to decline and have created some
conservation concern. In Ontario, some species are considered
endangered (Acadian Flycatcher, Prothonotary Warbler),
threatened (Hooded Warbler, Red-headed Woodpecker), or of
special concern (Cerulean Warbler, Louisiana Waterthrush),
because their populations have been dramatically reduced, while
other species remain relatively common despite steady
population declines (2.2 percent per year Wood Thrush;
1.9 percent per year Rose-breasted Grosbeak (see Bird Species of
Concern table page 88). Even so, there have been a few species
that have responded favourably to human habitat alteration and
have increased in population size and/or expanded their ranges,
including American Robins and House Wrens. Most species
threatened or in decline are Neotropical migrants; species who
6
Introduction