Dr. Vince Crichton with a fascinating look at "incidental wildlife mortality"

By Dr. Vince Crichton

Incidental wildlife mortalities! Have you ever thought about it? A recently published study from the United States brings an interesting perspective to the topic that may interest readers. 

The document is one of the most comprehensive ever done and involved a review and analysis of two dozen studies and over 92,000 records following which the authors estimate that between 365 and 988 million birds are likely killed in the United States each year as a result of collisions with buildings. 

One quote from this study is noteworthy: “Our analysis indicates that building collisions are among the top anthropogenic threats to birds and furthermore that several bird species that are disproportionately vulnerable to building collisions may be experiencing significant population impacts from this anthropogenic threat”.

This study provides quantitative evidence to support the conclusion that building collisions are second only to feral and free ranging pet cats (estimated that they kill as many as 3 billon birds (not a typing error!!) each year) as the largest source of direct human caused mortality for U.S. birds. And, many of these birds nest in Canada.

Those species most commonly reported as building kills were white throated sparrows, dark-eyed junco, ovenbird and song sparrow. The study did find that some species are disproportionally vulnerable to building collisions and several of these species are of national conservation concern and primarily fall victim to certain building types. 

These include: the golden winged warbler and Canada warbler (low-rise and high rise buildings); painted bunting (low rise); Kentucky warbler (low and high rise); worm eating warbler (high rise); and wood thrush (residences). For some species that are vulnerable to collisions at more than one building class, mortality appears substantial and may worsen population declines.

Although the study was focused in the United States, reports that I have seen over the years clearly show that the problem also occurs in Canada. I recall hearing of workers in Toronto picking up dead birds in the morning that had died overnite after colliding with high rise buildings.

Can we as home owners help? There are tips offered which can help: affix a pattern of tape or other material to windows which makes glass visible to birds. Most birds will avoid windows with vertical stripes spaced four inches apart or horizontal stripes spaced two inches apart. 

For best results patterns must be on the outside of windows. A specialty, easy to use and inexpensive tape can be found at ABCBirdTape.org. Another option is to use a lightweight netting, screen or other material over the window but it must be several inches from the front of the window to ensure birds do not hit the glass after hitting the net.

 Some may think that the 2 or 3 birds hitting one’s window is miniscule in the big picture but remember that all mortalities are cumulative thus if we all took precautionary steps our cumulative effort will make a difference.


I am sure most readers, like myself, will have wondered, as we drive our highways and see the carnage of dead wildlife, how many are killed on an annual basis. I recall a report stating that about 4,000 deer are killed ‘daily’ on the highways in the United States – mind boggling but when one sees the latest hunter harvest figures for various States this figure becomes more believable. 

Following are the 2013 harvest statistics for some States: 144,404 deer in Kentucky; 125,635 in Indiana; 99,406 in Iowa; and 171,000 in Ohio – 4,000 per day killed on U.S. highways likely is realistic! 

Annually, I return to my home town (Chapleau)  in northern Ontario and always see dead moose on the highway especially along the north shore of Lake Superior. This stretch of highway from Thunder Bay to Sault Ste. Marie annually has dozens of moose/vehicle accidents that vary from cars, trucks, buses to delivery vehicles. 

According to retired Ontario wildlife biologist Gord Eason from Wawa, the Ontario Department of Highways annually spreads 40 metric tons of salt per mile in winter along this highway which is the primary attractant for moose.

 Gord has done extensive work in the Wawa area to try and make the salt pools less attractive to moose by placing pallets in the wet areas and draining the standing water.

I have also noted the large number of dead porcupines on Ontario highways. When discussing this with a friend employed with the Ontario Department of Highways he stated that they have a major problem with porcupines knawing the wooden guard rails placed along the highway at strategic locations – there is something in the treated posts attractive to these rodents. 

This prompted my wife and I to tabulate the location of dead porcupines and most were at guard rails or with 100m of them.

Now, there are other incidental mortalities relative to big game. Males of our big game mammals engage in some epic battles during the breeding season and trauma inflicted during this period can result in mortality either from locked antlers or from injuries and subsequent infections sustained during these confrontations. 

But, both sexes and the young can and do die from deep snow and starvation due to their inability to freely move about to food sources. The energy expended to move through deep snow as we see this winter in many areas of Manitoba does use up fat reserves resulting in death. Avalanches also kill big game as was seen a few years back when such an event occurred in Banff National Park killing a small but significant caribou herd.

Antlered animals can become entangled in abandoned phone or hydro lines. I have found moose that have died from such events and in one notable case the wire was wrapped around the nose and throat suffocating the animal but the fight before it died was so intense that one antler was broken. 

There are reports (and I have personally seen this in Manitoba) of moose and deer being caught in snares set for smaller game such as wolves and coyotes. And, there are more bizarre events. In one case a moose was feeding along a river bank in winter while standing on deep but hard snow, fell through and its head stuck got stuck in the fork of a tree from which it was unable to dislodge itself. 

This also occurred with a bull elk in Manitoba’s Duck Mountain – while standing on hard packed snow, the snow gave way and the antlers became entangled in a tree and the animal essentially hung itself. 

As a point of interest the antlers from this animal when measured stand in second place in Manitoba. I once had a radio collared moose fall into a rock crevice in Manitoba’s Interlake from which it was unable to extricate itself and died. 

And, the most bizarre occurred in the Gulf of Alaska when two moose swimming to an island were caught by killer whales and subsequently killed and consumed.

There are other examples but suffice to note that incidental mortalities are significant mortality factors and we as humans must conduct our activities in such a way as to minimize these events.

NOTE OF THANKS: Dr. Vince Crichton, who was born and raised in Chapleau, Ontario, is a leading wildlife biologist with an international reputation in his field. Vince is a leading expert on moose. Thanks so much for your insights into "incidental wildlife mortalities". MJM