Loggerhead Shrike

 Why the Carden Alvar?

Ron Pittaway

First published in the Toronto Ornithological Club Newsletter, April 2018, Number 276

Introduction: The Carden Alvar is one of the last two nesting strongholds (Carden and Napanee) of the endangered Loggerhead Shrike in Ontario. The shrike is a high priority bird sought by birders visiting the Carden Alvar. Why is Carden ideal habitat for Loggerhead Shrikes? Below I’ve divided shrike breeding habitat into three key components: habitat structure, cattle grazing, and forbs.

Habitat Structure: In Carden, shrike nesting territories consist of scattered or clumps of hawthorns bordering wide meadows for hunting. Isolated trees, shrubs and tall mullein stocks are important lookouts. Shrikes also prefer short-grass meadows because they typically hunt prey such as beetles and grasshoppers on or near the ground.

Cattle Grazing: Cattle are essential to the maintenance of shrike habitat in Carden. Grazing keeps the grasses short and at uneven heights, increasing diversity. Cattle also attract and disturb insect prey. Ungrazed pastures become unsuitable breeding habitat for shrikes because they overgrow with tall grasses, shrubs and trees.

Carden Alvar Loggerhead Shrike by Jean Iron

Forbs: Compared to most farm fields, Carden’s prairie-like alvar meadows have a high percentage of forbs. Forbs are herbaceous flowering plants such as wildflowers, but not grasses, sedges or rushes. Forbs greatly increase the biodiversity and productivity of alvars. Riley (2013) says that alvars are “hotspots for plant and insect diversity”. They provide abundant food for grassland birds such as Loggerhead Shrike, Upland Sandpiper, Eastern Meadowlark and Vesper Sparrow.

Habitat Management: The three habitat components discussed above point to the Loggerhead Shrike being a “habitat specialist” in Ontario (Pittaway and Iron 2004). Habitat specialists have narrow ecological requirements whereas generalists can use a larger range of habitat conditions. Fortunately, Carden’s meadows are being managed for shrikes with actions such as prescribed grazing, prescribed burning (trials), removal of dense thickets, and landowner incentives and agreements to maintain critical habitat for Loggerhead Shrikes. Wildlife Preservation Canada is the lead agency in the recovery of the Loggerhead Shrike.

To see a Shrike: Ecologist John Riley of the Nature Conservancy of Canada wrote "The Carden Alvar is Ontario's second most important birding destination". The most reliable spot to see a Loggerhead Shrike is to scan the hawthorn pasture  west of bluebird box 10 near the viewing stand on Wylie Road. Also check for shrikes in grazed areas along McNamee and Shrike Roads, and scan the Cameron Ranch from the parking lot adjacent to Kirkfield Road.

References:

Pittaway, R. and J. Iron. 2004. Is the Loggerhead Shrike a Habitat Specialist? OFO News 22(3):16

Riley, J. 2013. The Once and Future Great Lakes Country: An Ecological History. 516 pages. Published by McGill-Queen's University Press.

For more information Please see Ron Pittaway's Carden Alvar Birding Guide