Movement Ecology of Animals

Homepage of Dr. Emily A. McKinnon

Connecticut Warblers fly over the Atlantic for 2 straight days in the fall


Yep. Move aside, Blackpoll Warblers. There’s a new trans-Atlantic fall migrant in town. Okay, actually Connecticut Warblers have probably been doing this for thousands of years, but it’s pretty surprising because we didn’t know it until now.

In my Scientific Naturalist paper in Ecology (or download directly McKinnon_et_al-2017-Ecology), I show how 4 Connecticut Warblers flew from the coast of the US for two solid days (minimum of 48 hours) over water to land somewhere in the Greater Antillean islands, probably Hispaniola. To make it even more stunning, they rested for about a week, then again flew almost 800 km over open water to the Gulf of Venezuela. And they weren’t done yet! They continued south to winter somewhere deep in the Amazon basin. The data are a little blurry on the exact wintering sites, but somewhere deep in the green that is the Amazon forest.

In contrast, the ocean-crossing is as clear as day because, well, there are no trees over the ocean! So when we are using light-sensors to track migration, it’s really obvious when the birds are not experiencing any shading at all from trees or other vegetation. The light levels just steadily increase and then decrease as dusk falls. In contrast, when the birds are on land, it’s a mess of light-levels going up and down, even as low as zero when birds are in really shady spots (giving us dozens of artificial ‘sunsets’ that we have to filter out). This is partly to blame for our fuzzy delineation of the exact overwintering sites for these individuals. The Amazon forest understorey is a dark place!


Connecticut Warbler with a light-sensing geolocator backpack. This was one we put out this past summer (2016) so we hope this bird comes back this year (2017)! The stalks will hopefully give us better resolution for identifying wintering sites. The original tags we used were stalk-less and had a lot of shading from the feathers.

Back to the fall migration of this species – how did we miss this amazing feat of migration?

I think there are a lot of reasons, actually. First of all, Connecticut Warblers, on a global scale, are not very abundant, so they are not a species commonly captured or seen by banders or birders. They nest in the southern-boreal aspen-transition habitats in Manitoba, Ontario, Quebec, and some parts of the northern Great Lakes states like Wisconsin and Michigan, but they are not common even within their breeding range. Not many people venture out into bogs in June in Manitoba either, and I know why!


Feeding the healthy mosquito population while catching Connecticut Warblers

Okay, so not a lot of overlap between people and Connecticut Warblers (a range map is in my previous post on these guys). I also think that Connecticuts probably get confused with their more southern-breeding cousins, the Mourning Warblers, or their western cousins, MacGillivray’s Warblers. This would be especially the case in the fall, where the young-of-the-year in those species might actually have a complete eye ring like a Connecticut Warbler (normally they only have semi-circles, as in MacGillivray’s, or none, like the Mourning).

So all of this means that coming across one of these guys and positively identifying it in the fall especially might be tricky.

But we had some hints that they might do something drastic over the ocean. Hurricane Emily brought down 75 individuals on BERMUDA one October. What would they be doing way the heck over the ocean?!? There is also a really neat video capture of a flock following cruise ship lights in the Lesser Antilles. Finally, the famous ornithologist Alexander Chapman commented on how darn FAT Connecticut Warblers were in the fall in the northeastern states… hmmm, suspicious, no?

Now that we have some tracking data, I can see additional reasons why we would miss this. First of all, if their major Caribbean stopover is on Hispaniola, it would be easy to miss. Hispaniola’s landscape is rugged, and humanitarian crises have resulted in few bird surveys there in recent decades. Unfortunately, it’s also lost a lot of forest recently- something like 90% of the original forest cover in Haiti is gone! Yikes.

Now that we know Connecticut Warblers travel through this area, hopefully we can get some more details on what type of habitat they might use or need for these Caribbean stopovers. Clearly their strategy relies on extraordinarily long migratory flights, which suggests they also need extraordinary amounts of fuel in advance of these flights as well as for recuperation after.

For Connecticut Warblers, I hope this study gives them some well-deserved time in the spotlight. They’ve been missing in action for too long, and I don’t want them to end up missing in action for good!

Full citation for the paper plus links to download a pdf and supplemental files:

McKinnon, EA, Artuso, C., and OP Love. 2017. The mystery of the missing warbler. Ecology. 10.1002/ecy.1844


ecy1844-sup-0001-AppendixS1 (1)



Connecticut Warblers of Manitoba.



4 thoughts on “Connecticut Warblers fly over the Atlantic for 2 straight days in the fall

  1. This is good to see, confirming a suspicion that I and quite a few others have entertained for decades, with quite a few points supporting that suspicion:

    1) A very similar pattern of occurrence in the eastern US in fall to that of Blackpoll Warbler (BLPW), with a huge hole in the southeast —

    2) The regular occurrence on Bermuda in fall, a la BLPW (only less findable) —

    3) The very pointed wingtip, with the only parulid having a more-pointed wing being BLPW.

    So, while some of us are not surprised by the results of placing geolocators on Connecticuts, we are quite happy that someone has finally done the work and I congratulate you on that!

    • Yes, we were thinking the same things as you for sure regarding points 1, and 2 above. Point 3 is interesting – the wingtips being more pointed. Do you have a citation you could direct me to for this comparison? I’m wondering if it might be something I should measure in the field this year… field season starts in less than a week!

      • Hey:

        My first understanding of this was as a subsidiary unpublished aspect of a friend’s work that was published in Auk (; I cannot get the PDF to open on my phone, so…). Additionally, I have caught and banded >50 of both BLPW and CONW and wing shape has long been an interest of mine, as it represents a fascinating example of dynamic tension between habitat and migration distance.

        Unfortunately, wing point and/or wing formulae are not features regularly noted in Pyle (1997, 2008). You might, however, check that source on the off chance that it is noted for CONW. My recollection is that wing point on BLPW is solidly on p8, while that of CONW varies between p7 & p8 (possibly with the mean on the p8 side; it’s been a long time since I handled either sp.).


        Tony Leukering currently Guymon, OK


  2. Pingback: Year of the (female) Bird Biologists | Movement Ecology of Animals

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s