A Bird’s Eye View: How are Breeding Birds Faring in the Greater Toronto Area?

Most people pay attention to birds during early spring when songbirds permeate the air with their delightful tunes. But it is not until late May when ecologists from Toronto and Region Conservation’s (TRCA’s) Environmental Monitoring team begin to listen to and record the presence of breeding birds in regional forests, meadows, and wetlands.

TRCA environmental monitoring breeding bird survey
Members of TRCA’s Environmental Monitoring Team conduct a breeding bird survey in King City.

TRCA has been collecting data on bird, vegetation, frog and salamander communities at fixed sites throughout TRCA’s jurisdiction since 2008 to be able to report on population trends over time and across the landscape. TRCA recently published its findings from this program in the Terrestrial Long-Term Monitoring Report: Spatial and Temporal Trends 2008-2014. Summary findings for bird communities show that regional bird population trends are relatively stable over time, but all are showing signs of impairment in more urbanized areas, especially forest birds.

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Spotlight on Forest Birds

The report highlights how the number of forest-dependent birds is lower in urban forests compared to rural forests, including regional Species of Conservation Concern (SOCC). Most rural sites contained two SOCC while the majority of urban sites often contained one or no sensitive species.  At first glance the rural land use zone appears to be able to better support sensitive species compared to urban areas. Further analyses of the rural land use data, however, suggests that we are possibly seeing a decline in the forest bird community overall as a result of encroaching urbanization.

TRCA environmental monitoring breeding birds

Of utmost concern is the decline of low-level nesting birds in rural forests. Birds that nest and forage on the ground are extremely susceptible to increased traffic and noise from hikers and off-leash dogs that do not stay on the trails.

One study reported that dog walking in natural habitats caused a 35% reduction in bird diversity and a 41% reduction in abundance, with even higher impacts on ground-nesting species (Banks and Bryant 2007). If ground-nesting birds are repeatedly chased from their nest, the stress can cause them to abandon their breeding activities. The breeding period in particular is a critical time for birds as they have reduced energy from nest building, egg laying, defending their nests and feeding of young.

Forest bird communities in the urban and rural land use zone also differed based on the 10 most abundant species per station.


TRCA environmental monitoring breeding birds   TRCA Environmental Monitoring breeding birds

Several factors are thought to be influencing this variation in forest bird community composition and sensitive species between rural and urban areas. For example, forest fragments in a highly urbanized setting are often small areas that are exposed to increased recreational activities, off-leash pets, predators and nest parasitism by brown-headed cowbirds.

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These combined pressures may be excluding area-sensitive forest bird species that need large tracts of forest for breeding and foraging (Austen et al. 2001). Some studies show that predation and parasitism rates are so high in forest fragments that breeding populations do not have enough surviving offspring to sustain future generations (Robinson et al. 1995; Burke & Nol, 2000). For example, high housing densities are known to contain a larger abundance of blue jay, domestic cats, raccoons and opossum (Haskell et al. 2001).

In Summary

It is apparent from these results that long-term terrestrial biodiversity data collection is imperative in order to make appropriate decisions relating to climate change, land development, restoration activities, environmental protection and management of natural areas in the future. Long-term terrestrial monitoring is expected to continue in both the urban and rural land use zones, with a focus on temporal impacts of development on natural areas that are currently changing from rural to urban land uses.

Monitoring Matters! Through scientific data collection, TRCA’s Environmental Monitoring and Data Management team tell the stories about the changes affecting the natural areas and watercourses within our regions.  For more information, please visit our webpage, follow us on Twitter, subscribe to our Monitoring Matters e-newsletter, or visit our YouTube playlist.