I think Lyle Friesen says it best in his write-up on the Gray-cheeked Thrush in the 2nd edition of the Atlas of the Breeding Birds of Ontario: 2001-2005: “The Gray-cheeked Thrush remains a scientific enigma, certainly deserving of more extensive research and attention throughout its range.”

And what a range!!! It nests from Newfoundland to the Chukchi Peninsula in eastern Siberia and spends the winter in northwestern South America (Venezuela, Colombia and northern Brazil. In June of 2014 I was involved in a study of Canada Warblers in the Fort Liard area (southwestern Northwest Territories). I was excited about catching and banding Canada Warblers for sure but I was also excited about the possibility of banding Gray-cheeked Thrushes. But, alas, Fort Liard is much too far south for breeding Gray-cheeks!

We occasionally catch this species in the Spring (usually 1 or 2 per Spring) but we catch them regularly in the Fall in modest numbers (335 in 20 years). One thing we notice about Gray-cheeks as opposed to Swainson’s Thrushes in the Fall is that the former usually carry more fat and, in some cases, a lot more fat. One Gray-cheek that we had weighed just over 52 grams – more than twice as much as its fat-free weight (~24 g.). This particular bird was quite interesting in that it stuck around for about 10 days. We retrapped it another 3 times and each time its weight went up until it reached 52 grams. I figured it would have a hard time taking off and carrying a load like that without some support. Sure enough, a high pressure system went through with strong NW winds. We never saw the bird after that and I can only conclude that it got the winds it was waiting for and took off.

Now birds aren’t like humans when it comes to fat. I mean, why carry around a lot of extra weight at great cost to yourself when there’s no need? But….why put on so much weight when you’re migrating. A large proportion of passerine migrants go in relatively short “hops” – 100 to 200 kilometers a night when they’re inclined to go. At a comfortable speed of 30 km/hr that would be only 3-6 hours of flying and this level of exertion would certainly not require a bird to double its normal weight. But all birds, even of the same species, do not necessarily follow the same game plan when it comes to migration. Some, rather than move in short hops, take big jumps. And I’m sure this is what this particular Gray-cheek was doing. Energetically this bird was carrying enough energy to fly non-stop from Ruthven to South America (and still have some to spare).

But this was all conjecture: the bird had enough fat/energy; it could have flown non-stop with that level of energy; it left when there was favourable wind assistance….but do these birds really do this?

I just read in Bird Studies Canada’s most recent Newsletter about some of the results they were finding through their involvement with the Motus Wildlife Tracking System. Technology is transforming the study of bird migration….migration generally. With the Motus system, tiny, light-weight “nano-tags” are affixed to a bird’s leg. These little transmitters emit a signal that can be picked up by receivers built for the purpose within about a 20 kilometer radius (hypothetical maximum). The network of receiver towers is ever expanding and can be found on the coasts of Hudson and James Bay, the eastern Great Lakes, mouth of the St. Lawrence, the Maritime Provinces, the Eastern Seaboard of the U.S., and right down into Colombia.

Several Gray-cheeked Thrushes, tagged in Colombia have been tracked on their northern/Spring migration using this system. One made a flight of 5,338 km in 29 days (averaging 184 km/day); another travelled 3,674 km in just 13 days (283/day). These are impressive flights and you have to read in-between the lines: the number of days taken suggests that these birds stopped and refueled along the way (sometimes for a day or two – especially if weather conditions weren’t conducive to migration) so some of their flights would have been much longer. But the bird that most intrigued me was one that covered over 3,200 km in just 3.3 days!! This would have had to have been a non-stop flight: 970 kilometers per day at 40 km/hour!
Now that is amazing!
Rick