catch me if you can researchers scramble to explain declining kestrel popul

Trying to research a bird that is disappearing is a nearly impossible task, if you ask Dave Mossop. The Yukon Research Centre biologist has been studying the American kestrel - North America's smallest falcon - since the 1980s.

by Vivian Belik

Trying to research a bird that is disappearing is a nearly impossible task, if you ask Dave Mossop.

The Yukon Research Centre biologist has been studying the American kestrel – North America’s smallest falcon – since the 1980s. In those two decades, numbers of American kestrels in the Yukon have plummeted by 80 per cent. A bird that was once plentiful on telephone wires across the territory is rarely spotted these days.

“It’s a real catastrophe and a wake-up call,” says Mossop, who became interested in the American kestrel by accident. He wanted to find out how larger birds like boreal owls and ducks were able to find nesting cavities in small Yukon trees. The kestrel also finds refuge in tree cavities, most often those left over from woodpeckers. While Mossop was tracking these cavities, he realized that the number with kestrels in them was dwindling. That was in the early ‘90s.

Mossop started networking with other bird biologists around North America to see if they were noticing a similar trend. But in the ‘90s and the early part of 2000, only the Yukon was experiencing significant declines, he says. That changed in 2009 when a research conference was held to discuss the American kestrel. “It turned out the decline was being seen everywhere at that point and that led to people raising the alarm.”

Although shrinking kestrel populations are being noticed all across North America (in the last half-century there’s been an overall 50 per cent decline), the Yukon has seen the most drastic drop in kestrel numbers. Being at the northern limit of the birds’ breeding range has a lot to do with it, explains Mossop.

“We’re in harm’s way for all kinds of changes and we see climate changes here more quickly than anywhere else in North America.” Birds that travel as far north as the Yukon are usually under more stress, he says.

Since Mossop’s realization in the ‘90s that kestrel numbers have been dropping, he’s been closely tracking the bird. “You’re trying to stop something that’s underway and study something that’s disappearing on you, and it’s quite tricky,” he says.

Biologists often band birds’ legs to track them, but kestrels aren’t hunted, so people aren’t picking up the bands. With so few birds left it’s also difficult to track them using modern devices like radio transmitters.

Instead, Mossop has set up 150 nest boxes around the territory, some as far north as the Arctic Circle. Kestrels make their homes in these man-made boxes, making it easier for amateur and professional birders to track the bird.

Mossop has been working with researchers across North America, using data from these nest boxes to piece together a picture of why kestrel numbers are in decline. The first culprit they identified was the Cooper’s hawk, a predator of the kestrel that has been known to “trap-line” nests in search of newborn birds. Scientists noticed that, throughout the ‘90s, the population increase of Cooper’s hawks coincided with the drop in kestrel numbers.

The other factor they considered was the West Nile virus, which is transmitted by mosquito bites and kestrels are susceptible to catching. However, when scientists examined the data, neither factor was significant enough to explain the decline.

Mossop now believes that pesticides used on farmers’ fields are to blame, although he cautions that scientists are still testing this theory. “The chemical industry never sleeps, creating new nasty things virtually every day,” he says. There’s a new pesticide in particular that he has his eye on that targets mice. In winter habitats, kestrels eat a lot of small mammals like mice, and any pesticides that the mice eat accumulate as you move up the food chain. “It just builds up inside the kestrels,” says Mossop.

It’s exactly the type of poisoning in birds that Rachel Carson, who wrote the seminal book Silent Spring in 1962, predicted would happen. Mossop points out that pesticides have already wiped out significant populations of larger raptors, like ospreys and peregrines.

But Mossop is also concerned by a severe drought that’s been occurring across the Pacific Southwest for the last half-decade. American kestrels migrate through this area and the drought appears to be affecting them, he says. “We need to start paying attention,” says Mossop. “It’s like an alarm bell going off. This little bird we share the environment with, they’re telling us something is wrong.”

This column is co-ordinated by the Yukon Research Centre at Yukon College with major financial support from Environment Yukon and Yukon College. The articles are archived at

Get local stories you won't find anywhere else right to your inbox.
Sign up here

Just Posted

Willow Brewster, a paramedic helping in the COVID-19 drive-thru testing centre, holds a swab used for the COVID-19 test moments before conducting a test with it on Nov. 24. (Crystal Schick/Yukon News)
An inside look at the COVID-19 drive-thru testing centre

As the active COVID-19 case count grew last week, so too did… Continue reading

Conservation officers search for a black bear in the Riverdale area in Whitehorse on Sept. 17. The Department of Environment intends to purchase 20 semi-automatic AR-10 rifles, despite the inclusion of the weapons in a recently released ban introduced by the federal government, for peace officers, such as conservation officers. (Crystal Schick/Yukon News file)
Environment Minister defends purchase of AR-10 rifles for conservation officers

The federal list of banned firearms includes an exception for peace officers

Yukonomist Keith Halliday
Yukonomist: The K-shaped economic recovery and what Yukoners can do about it

It looks like COVID-19 will play the role of Grinch this holiday… Continue reading

Jodie Gibson has been named the 2020 Prospector of the Year by the Yukon Prospectors Association. (Submitted)
Jodie Gibson named 2020 Prospector of the Year

Annual award handed out by the Yukon Prospector’s Association

A number 55 is lit in honour of Travis Adams, who died earlier this year, at the Winter Wonderland Walk at Meadow Lakes Golf Club in Whitehorse on Nov. 24. (Crystal Schick/Yukon News)
A new take on holiday traditions

Winter Wonderland Walk, virtual Stories with Santa all part of 2020 festive events in Whitehorse

Black Press Media and BraveFace have come together to support children facing life-threatening conditions. Net proceeds from these washable, reusable, three-layer masks go to Make-A-Wish Foundation BC & Yukon.
Put on a BraveFace: Help make children’s wishes come true

Black Press Media, BraveFace host mask fundraiser for Make-A-Wish Foundation

Colin McDowell, the director of land management for the Yukon government, pulls lottery tickets at random during a Whistle Bend property lottery in Whitehorse on Sept. 9, 2019. A large amount of lots are becoming available via lottery in Whistle Bend as the neighbourhood enters phase five of development. (Crystal Schick/Yukon News file)
Lottery for more than 250 new Whistle Bend lots planned for January 2021

Eight commercial lots are being tendered in additional to residential plots

The Government of Yukon Main Administration Building in Whitehorse on Aug. 21. The Canada Border Services Agency announced Nov. 26 that they have laid charges against six people, including one Government of Yukon employee, connected to immigration fraud that involved forged Yukon government documents. (Crystal Schick/Yukon News file)
Charges laid in immigration fraud scheme, warrant out for former Yukon government employee

Permanent residency applications were submitted with fake Yukon government documents

Whitehorse City Hall. (Joel Krahn/Yukon News file)
City hall, briefly

A look at decisions made by Whitehorse city council this week

Karen Wenkebach has been appointed as a judge for the Yukon Supreme Court. (Yukon News file)
New justice appointed

Karen Wenckebach has been appointed as a judge for the Supreme Court… Continue reading

Catherine Constable, the city’s manager of legislative services, speaks at a council and senior management (CASM) meeting about CASM policy in Whitehorse on June 13, 2019. Constable highlighted research showing many municipalities require a lengthy notice period before a delegate can be added to the agenda of a council meeting. Under the current Whitehorse procedures bylaw, residents wanting to register as delegates are asked to do so by 11 a.m. on the Friday ahead of the council meeting. (Crystal Schick/Yukon News file)
Changes continue to be contemplated for procedures bylaw

Registration deadline may be altered for delegates

Cody Pederson of the CA Storm walks around LJ’s Sabres player Clay Plume during the ‘A’ division final of the 2019 Yukon Native Hockey Tournament. The 2021 Yukon Native Hockey Tournament, scheduled for March 25 to 28 in Whitehorse next year, was officially cancelled on Nov. 24 in a press release from organizers. (John Hopkins-Hill/Yukon News file)
2021 Yukon Native Hockey Tournament cancelled

The 2021 Yukon Native Hockey Tournament, scheduled for March 25 to 28… Continue reading

Lev Dolgachov/123rf
The Yukon’s Information and Privacy Commissioner stressed the need to safeguard personal information while shopping this holiday season in a press release on Nov. 24.
Information and Privacy Commissioner issues reminder about shopping

The Yukon’s Information and Privacy Commissioner Diane McLeod-McKay stressed the need to… Continue reading

Most Read