What are the top 5 leading causes of bird mortality?
New research finds that a staggering 269 million birds are killed every year as a direct result of human-related activities. According to research released today, the top 5 human activities that are killing birds are:
- There are about 8.5 million pet cats in Canada, and 1-4 million feral cats.
- In total, 5-10 million of these cats are estimated to kill between 100 and 350 million birds per year in Canada, with about 60% estimated to be killed by feral cats.
- Of 461 bird species that regularly occur in Canada, 115 (25%) were identified as being potentially vulnerable to cat predation because they nest or feed on or close to the ground, especially in southern Canada.
- 23 species of Canadian birds that are classified as Species at Risk are among those species that are potentially vulnerable, because they spend time on the ground in areas where cats frequent.
- A similar American study, released in January 2013, provided comparable rates of bird mortality from cats in the USA using the same methodology developed for use in developing the Environment Canada estimates.
- Together, the results of these two studies provide considerable evidence of the high number of birds killed by cats in North America.
#2: Transmission lines
- Most direct mortality of adult birds caused by striking power lines occurs from collisions with transmission lines (251,750 km in Canada) which transport electricity from production areas to distribution centers (10.1 – 41.2 million birds/year).
- Most of these birds collide with shield wires, the uppermost wires above the actual transmission lines, which protect transmission lines from lightning strikes.
- An additional estimated number of 160,000 – 800,000 birds are electrocuted each year due to contact with distribution lines (572,370 km in Canada).
- These electrocutions generally kill large birds, such as eagles, hawks, owls, cranes, geese and swans, only about 10% which are migratory birds under federal jurisdiction.
- Key factors that affect the risk to birds from power lines include the orientation of the lines, power pole structure, local bird abundance, bird flight behaviour, weather and regional topographic features.
- The average rate of vegetation clearing under transmission lines, undertaken about every 5 years, results in an additional loss of about 388,274 nests/ year.
- As most studies of collision and electrocution casualties were undertaken outside Canada and tend to be site-specific, caution must be used in extrapolating these results.
# 3: Building collisions
- An estimated 25 million birds are killed annually by colliding with buildings in Canada (range 16 – 42 million), mostly at houses. The risk to birds of mortality from striking buildings is related to the height and type of building, the amount and location of glass windows present, and characteristics of surrounding lighting and landscaping.
- The estimated magnitude of bird mortality due to collisions with buildings are:
- Collisions with urban, suburban and rural houses: 16-30 million birds/year
- Collisions with low-rise commercial buildings: 0.3 - 11 million/year
- Collisions with high-rise commercial buildings: 40 - 250 thousand/year
- The number of collisions at houses is related to the density and number of birds present, so that higher rates of collision happen at rural houses and those with bird feeders.
- Birds most often reported killed in building strikes include finches, kinglets, warblers, and sparrows, including several species at risk.
- There are two main reasons birds typically fly into buildings:
- during the day, birds do not see the glass in windows, and attempt to fly through the window to habitat on the other side, or see a reflection of habitat which appears to be real; and
- at night, birds often become disoriented by lights and consequently strike buildings.
#4: Collisions with cars
- The estimated magnitude of annual mortality due to collisions with vehicles on Canada’s primary and secondary roads is about 13.8 million/year.
- The estimate does not include mortality on multi-lane highways or unpaved roads
- These vehicle collisions remove many healthy and mature breeding birds.
- About half the individual birds killed by vehicle collisions are songbirds, although little information is available about the actual species primarily affected.
- The destruction of nests with eggs or young is the most significant bird mortality caused by the forestry sector, rather than the direct killing of adult birds.
- Environment Canada scientists estimated that 616,000 – 2.09 million nests are destroyed annually due to commercial forest harvest activity. This loss of eggs and young translates into the equivalent loss of just under half this number of potential adult birds which are not recruited into breeding populations.
- Most significant forestry impacts on birds are likely for those species whose ranges are concentrated in areas of high forest harvest activity, such as southern boreal forests and mixed woods.
- Loss of nests due to forestry be a particular concern for species of national or regional conservation concern, in regions with significant centers of population abundance, such as Cape May Warblers in Saskatchewan, Canada Warblers in Manitoba, or Black-throated Green Warblers in Quebec
- Data limitations prevented the authors from estimating nest loss associated with forestry activities on privately owned lands. However, as about 19% of the timber harvested in Canada is from private lands, this may represent a significant additional source of mortality.
- Although nest loss is important, most population-level effects of forest harvesting on Canada’s birds result from huge changes in the characteristics and availability of bird habitats that occur when trees are removed, and which last for many years.
Nature Canada recommendations
In light of this shocking new research, nature conservation groups, including Nature Canada, are calling on both individuals and governments alike to act now to help stop millions of bird deaths each year.
What can individuals do?
- We have a major stray and neglected cat problem in Canada. For individual Canadians looking to help, we suggest that Bob Barker really was right: We need to help control the pet population and have our pets spayed or neutered.
- Our pets don’t understand the difference between an endangered bird species or not. Cats, in particular, are predatory animals by nature. Because of this, we strongly recommend people keep their cats indoors, especially around dawn and dusk.
What can cities do?
- To address the impact buildings have on birds, Nature Canada is calling on local governments to enact and enforce bylaws to help address this problem. These include:
- Putting in place and enforcing well-thought out building design standards to mute window reflections by angling glass or adding awnings or overhangs;
- Cutting down nighttime light pollution. Many companies and buildings have policies in place that keep the lights on during the evening even after workers have gone home. This is both wasteful from an energy conservation perspective and incredibly harmful to bird populations. Cities should to work to curb these practices wherever practicable.
- Making sure local governments have a good set of bylaws in place dealing with pet and stray cats. Cities also should make sure that they’re enforcing existing bylaws they have on the books regarding pets and stray animals.
- Nature Canada applauds the efforts some municipalities, like Toronto, have undertaken to help address this issue. Efforts like those of Toronto, however, are not yet complete or fully developed even where they have been attempted. What they do represent though is a good first step to addressing the problem. More municipalities need to develop a set of concrete policies along the lines of Toronto’s development guidelines. http://www.toronto.ca/lightsout/pdf/development_guidelines.pdf
What can other governments do?
- For its part, the federal government is obligated to conserve migratory bird populations under the Migratory Birds Convention Act and under the Migratory Bird Treaty. The federal government should provide concrete support to local governments to enable them to enact and/or enforce measures that can reduce bird mortality. This support can come in the form of direct funding or even by helping to establish a nation-wide, science-based “best practices” guidance document for cities to consult when enacting their local bylaws.
- Both federal and provincial governments have a big role to play. When undertaking environmental assessments of new energy projects, both federal and provincial governments should make sure we look at the project impact on birds, especially those species we have legal and treaty obligations to protect.