Statistics gleaned from annual breeding bird surveys over the past 30 years show that many prairie grassland bird species, such as the western meadowlark, redwing blackbird and killdeer, have been in serious decline largely due to habitat loss, according to Ken De Smet, a species-at-risk biologist with Manitoba Conservation.
Breeding bird surveys are conducted in much the same way all over North America, and the results for 256 species are compared from year to year to get an approximate picture of bird populations.
“When you are looking at these surveys that are done by the same people in the same areas, year after year, it is fairly observable over a wide scale that they have declined,” said De Smet.
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Each spring, around 50 volunteer bird watchers across Manitoba and 482 throughout Canada travel along the same routes and count how many of each species they spot.
To join the program, they must be able to identify various species by song and appearance, make a long-term commitment to the program and bring an assistant along to record their data.
“They are people who know their birds and enjoy doing it,” he said.
Although some prairie bird populations may be shrinking, the number of urban birds has been rising, including chickadees, woodpeckers and others better able to adapt to changing environments. House sparrow numbers, however, have been in decline.
“Most people wouldn’t believe that, but it may be related to some kind of disease or whatever,” he said.
On a positive note, the red-tailed hawk, blue jay, mourning dove and ruddy duck have increased in the last two decades, according to survey results covering 1967 to 2000.
“There are some species that have benefited, but for every one of those there are others that have really been declining seriously,” said De Smet.
However, short-term increases from one year to the next should be taken with a grain of salt. For example, spring kill can affect species such as barn swallows or bluebirds because they are highly dependent on insect populations. A two day storm in late spring about five years ago hit both species hard. Recovery could take several years, said De Smet.
“It was really fierce. People noticed dead birds all over the place. Sometimes one incident can really sway the numbers one way or the other.”
Although hawk numbers in general have been rising the past three decades, Northern Harriers, which are more reliant on native prairie grass areas, have declined.
The trend toward tearing up pastures and planting tame forages in their place may have had a negative effect on some bird habitats.
“Some species, like Baird’s sparrow, will nest in tame pastures, but probably they don’t do as well. Maybe the conditions are not as good for them,” said De Smet.
“For sure, the monocultures are tough on a lot of species. The more diverse habitat you have, certainly the better it is for wildlife.”
The widespread use of insecticides in recent decades may have played a role in the decline, but habitat loss is more significant in the long-term trend.
“I don’t think pesticides have had a huge effect on wildlife numbers. Maybe more on the food supply,” he said, adding that localized spraying might lead to nesting failure rather than killing a great number of birds outright.
“On the whole, I certainly wouldn’t put the blame on pesticides most of the time.”
None of the substances in current use has had as serious an effect as DDT, which was banned decades ago, he added.
De Smet said an overall change in habitat can send specialized species into decline. For example, the number of chimney swifts in urban areas went into freefall as chimneys were taken down or converted in many older buildings.
“Even bird watchers were surprised by the rate of decline.”
