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Hundreds of
species are considered "at risk" in Canada. Why focus on the Eastern
Loggerhead Shrike? One compelling reason is that grassland birds,
and the loggerhead shrike in particular, have shown a more persistent
and drastic decline than any other group of birds.
In fact, the Eastern Loggerhead Shrike has shown the greatest rate of population decline of any perching bird in Canada between 1970 and 1991. Shrike numbers have been in decline throughout North America since the International Breeding Bird Survey began in 1966.
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This is significant because wildlife scientists consider shrikes a "indicator" species among grassland birds. What affects the shrike also affects the Henslow's Sparrow, the Short-eared Owl, the Upland Sandpiper and other grassland birds that are becoming increasingly rare.
But the decline is also important on a broader scale because healthy shrikes mean a healthy environment. As predators, shrikes are near the top of the food chain. Their bodies accumulate toxins and contaminants from insecticides and other chemicals that their prey have already absorbed. In the same way, bald eagle populations declined in the mid-20th century because of toxic levels of DDT in the environment. Thus, like the proverbial canary in the coal mine, the shrike's declining numbers suggest an environment out of balance.
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| The exact reasons for the decline of shrikes across North America remain unclear. Still, ongoing research by shrike biologists and wildlife groups suggests that there are four main causes: |
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Loss
of habitat
There was a
39 per cent decline in unimproved pasture in the Prairie provinces
from 1946 to 1986. In southern Ontario, 65 per cent of prime Eastern
Loggerhead Shrike habitat has vanished over the past 50 years.
These losses
stem from changing land use patterns, new farming methods, increasing
urbanization and other factors.
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Chemicals
Pesticides, herbicides and other chemicals have proved to be detrimental to the health and reproductive success of many bird species in Canada and elsewhere. Scientists are now working to determine if, and to what extent, chemicals may be affecting the health of shrikes.
Increased mortality and predation
Many predators of shrikes have increased because of human-induced changes to the landscape. House cats, for instance, have become a problem. As shrike habitat shrinks, the birds and their potential predators must share the same fragments of remaining habitat. Consequently, shrikes are more likely to suffer from increased mortality and nesting losses due to predation.
Accidents
Shrikes nest in and hunt from trees and shrubs that are usually part of the border around a property and near roads. Unfortunately, shrikes are sometimes killed in collisions with passing vehicles.
One way to reduce collisions is to encourage drivers to slow down by posting "Endangered Species Ahead" road signs in appropriate areas.
Many key questions about shrikes remain to be answered, and The Eastern Loggerhead Shrike Recovery Program is only one of the many groups and individuals across North America working to answer them. These questions include:
- What are the causes of the shrikes' dramatic decline?
- What are the shrikes' migration routes, and where are their wintering grounds?
- Why do shrikes choose one location over another?
- What aspects of habitat improve breeding success?
- What affects the ability of shrike eggs to hatch, and the survival of hatchlings?
- What percentage of young survive to adulthood?
- What percentage of young and adults return, and what factors affect their survival in migration and wintering areas?
- Could capturing and breeding wild birds and releasing their offspring back to the wild increase shrike numbers?
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