Movement Ecology of Animals

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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


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Connecticut Warblers of Manitoba.



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The most interesting boreal bird you’ve never heard of

Spring is on the horizon and birders everywhere are starting to get antsy for those first early migrants. This year is a very exciting one for me, as I’m waiting for the return of one of my newest study species – one of the most mysterious boreal songbirds out there. Right now, ‘my’ birds are out there with tiny data-logging backpacks on, fattening up deep in the jungles of South America, waiting to head north.

Let’s see if you can guess who they are. These small warblers are long-legged, but not always found on the ground; they are colourful, but camouflage well; they are loud songsters, but largely quiet on migration, and often missed at breeding sites; they breed in open bogs, mature aspen forest, or mature mixed woods, but most people live far away from their breeding range; they look very similar to two other warbler species, but they are genetically distinct so placed in their own genus. Here’s a recording I made of one this past spring if you need a big hint:

The answer is… Connecticut Warbler (Oporornis agilis)!

First let me just explain that this unfortunately-named species has little or nothing to do with Connecticut, at any point in its life cycle! The name came from a single specimen that was ‘collected’ (i.e. shot) over the state of Connecticut in 1812 by Alexander Wilson. A better name for this species might be something more physically descriptive, like blue-headed or eye-ringed warbler, or maybe something related to habitat, like boreal bog warbler.


Check out that beautiful eye ring! Thanks to my field tech @KelseyDBell for taking the photo

In general Connecticut Warblers have a reputation for being mysterious, shy, retiring, skulky, rare, or even ‘sluggish’! After my first field season with this species this past summer, I think this reputation is because most birders only ever see Connecticuts during migration, and they are fairly rare and quiet during this period. Connecticut Warblers also migrate later in spring than a lot of other species, so they easily miss peak spring birding in May. Fortunately for me, living in Manitoba, at the edge of the boreal forest, Connecticut Warblers can be found breeding within 45 minutes’ drive of my house! Delving into the scant literature on this species last winter, I realized that we might actually be losing the Connecticut Warbler before we even know anything about it.

Long-distance migratory songbirds as a group are showing population declines across North America – my previous study species, the Wood Thrush, shows a fairly typical pattern of about 2% population loss per year over the last 40 years. The data for boreal songbirds are a little less strong because the breeding bird surveys used to generate population trends tend to peter out as you go further away from human population centres. However, many boreal songbirds are very long-distance migrants (i.e. they go all the way from the temperate boreal to South America), which is a big risk factor, and the trends that we do have don’t look very promising for most, including the Connecticut Warbler. Overall, the Connecticut Warbler is declining by about 1% per year. Most of the Connecticut Warbler breeding range is in Canada, which means that Canadians in particular have a responsibility to protect this bird.


This map shows the Breeding Bird Survey trends over the last 40 years, with areas in red declining the most and areas in blue increasing. Overall the Connecticut Warbler gets a ‘medium’ confidence in terms of how real these trends are – this is because there aren’t as many survey routes in their range as we would like, and their density is generally pretty low.

One of the potential threats listed for this species is habitat loss in the winter range. But critically, we have nearly zero information on migration, winter range, winter habitat, or winter ecology. There are only 5 ebird records for this species in the winter range. One in Bolivia, the rest in Colombia. Records in the literature are equally sparse. It’s hard to believe that a North American breeding bird could be so under-studied. Dr. Jay Pitocchelli and colleagues recently (2012) updated the Cornell Lab of Ornithology’s Birds of North America Species Account for Connecticut Warbler, and it is clear there are still huge gaps in our knowledge of this species. For one, it took 70 years after the original specimen was collected for a nest to be described. What we know about breeding biology is largely from a very detailed study of ONE nest in Michigan in the 1960s. Reading through the BNA Account had me more and more intrigued. Then I read this: “Some evidence for nonstop trans-oceanic migration (Monroe 1968, Wetmore et al. 1984) […] Records for West Indies are scarce, but large numbers were reported on Bermuda during Hurricane Emily on 26 Sep 1987 when 75 were grounded; previous daily high had been 3 (Amos 1991).”

Could Connecticut Warblers be trans-oceanic fall migrants, like Blackpoll Warblers? 

Examining the ebird records for the fall migration period were also suggestive of a trans-oceanic flight. Connecticut Warblers are rarely detected along the gulf coast or in Florida, and there is only one ebird record for all of Central America (Panama). In contrast, they have been spotted throughout the Lesser Antilles and into northern South America. Could they be flying over the ocean from the east coast of the US directly to the Lesser Antilles or even direct to South America?


Examining records for Connecticut Warblers shows the potential for a trans-Atlantic flight in fall.

Given the total lack of information on fall migration routes and winter sites, and the potentially mind-blowing fall migration this species might undertake, and the fact that they are a designated stewardship species of the northern forest, they are a prime candidate for migration tracking!

After convincing my supervisor Dr. Oliver Love and mentor Dr. Christian Artuso of Bird Studies Canada that this was worth investigating, last summer I captured over 30 males, and put out tiny 0.5 g data-logging backpacks on 29 of them. These tags are passively recording light levels and hopefully the birds return (with their backpacks intact!) this spring to their breeding sites near Winnipeg, Manitoba, where I will be waiting for them! I suspect they have important stories to tell.

Stay tuned for Part 2: Connecticut Warbler Fieldwork (or, how everything I thought I knew about them was wrong)



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Bicknell’s Thrush nests in regenerating clearcuts in the highlands of New Brunswick

Bicknell’s Thrush (Catharus bicknelli) is one of those birds that real twitchers lust after. It’s hard to identify in the field, especially outside of the breeding season, and it’s range is patchy and limited to northeastern North America and a couple of islands in the Caribbean. Its secretive nature, dense foggy breeding and wintering habitat, and mournful song only add to the allure. Unfortunately, like too many other songbirds, Bicknell’s Thrushes are steadily disappearing. This is particularly so in the highlands of New Brunswick and Nova Scotia, Canada, where I did my Masters research on this species. A recent report by Bird Studies Canada’s High Elevation Landbird Program (HELP) showed a decline of 11% ANNUALLY over a 10-year time period! Yikes! Bicknell’s Thrush is now federally listed as THREATENED in Canada.

Super dense balsam fir forest preferred by Bicknell's Thrush

Super dense balsam fir forest preferred by Bicknell’s Thrush

One potential problem for Bicknell’s Thrush in New Brunswick is a logging practice called Precommercial Thinning (PCT). Bicknell’s Thrush nest in very dense forests that regenerate on mountain-tops in North and North-central New Brunswick. Where I worked, in the Christmas Mountains, the highest peaks are around 600-700m above sea level. Not very big relative to other mountains, but enough, at this high latitude (~46N) to create fairly harsh conditions. Balsam fir and white birch thrive up there, especially after clearcuts. The balsam fir grows back at such a high density that the trees stunt their own growth through crowding. This is no good for logging companies interested in the best bang for their buck. To help improve the growth of the trees in a given patch, loggers go in and ‘thin out’ the forest by PCT, when the trees are about 10-15 years old (about 2-5 cm in diameter). It’s pre-commercial because the trees they cut down aren’t at a size to be of much commercial value – they are just cut and left lying on the ground. What this practice does overall is to remove about 75% of the trees in the forest, with the idea that the remaining 25% will be better off for it.

This practice affects Bicknell’s Thrush because they too love high elevations, and they really really love balsam fir. I collected data on a dozen or so nests of Bicknell’s Thrush during my Masters, and every single one of them was in a balsam fir. The only one that was not entirely in a balsam fir was squished between a fir and a spruce. So when the forests at high elevation are basically perfect Bicknell’s Thrush nesting habitat, loggers come in and cut down 75% of the trees! You can see why this is concerning to people interested in preventing further population declines of this species!

Rolling hills of north-central New Brunswick - few people, lots of logging roads!

Rolling hills of north-central New Brunswick – few people, lots of logging roads!

I wanted to know more about the habitat Bicknell’s Thrush used for nesting, and if they ever nested in forest that had been thinned. Imagine a female Bicknell’s Thrush, returning to North Pole Mountain (yes, the Christmas Mountains have Christmasy names!) in the spring, after spending the winter in the highlands of the Dominican Republic. She gets back to the forest she nested in last year, only to find that most of the trees are gone! Does she go for it anyway? Or fly onward to another mountain? Or just move to the unthinned forest next door in hopes it will stay dense for another nesting season?

I can tell you exactly what one female did.

Finding Bicknell’s Thrush nests is like finding a needle in a haystack, only imagine that the needle is camouflaged and the haystack is several hectares large. Against all odds, we found several Bicknell’s Thrush nests over the course of our project, and in our first year, they were all in unthinned forests. We carefully monitored each nest with minimal disturbance, sometimes using video cameras. We tried to capture all the adults feeding the chicks and band them with a unique colour-combination of plastic rings on their legs. Bicknell’s Thrush are an unusual songbird in that they have multiple ‘dads’ that father and help feed the chicks, so a single nest could have 3 or even 4 parents attending the chicks! One of the few females we captured was nesting in a forest that was scheduled to be thinned. Bicknell’s Thrush, like many songbirds, are highly site-faithful, which means they return to the exact same forest patches for nesting year after year. What would this female (her ID was light-green-mauve-black-silver) do when she came back the next year to a thinned forest?

Can you spot the blue eggs?

Can you spot the blue eggs?

The following spring, we searched and searched in the thinned forests and found no signs of any Bicknell’s Thrushes, let alone nests. In a very small dense patch in a boggy area, right across the logging road from light-green-mauve-black-silver’s original forest patch, we did hear a Bicknell’s Thrush singing. It was such a tiny and miserable forest patch (standing water, dense tangles of dead balsam fir, logging roads on either side of a wedge about 10m wide) that we pretty much gave up finding any nests there and figured the singing male was overly optimistic about his chances. Finally near the end of the nesting season, I decided it would be worth going back to this patch for one final search.

My crew dropped me off and I steeled myself for the scratchy squeeze through the dense boggy patch one more time. I finally popped into a bit of an open area and froze. I had hear a distinct ‘Peer!’ call from very close by. This is a call Bicknell’s Thrush often use, but I noticed on our nest videos that females often gave it when they jumped off the nest, either to let Dad in to feed the kids, or because of some disturbance nearby. Like me. I looked around very carefully. There were no branches with needles on them below my head height – the needled branches were all above me, creating a dense canopy about 5-m tall. Then I saw it – way up high, pressed against the trunk of a balsam fir, a messy clump of nesting material! Could it be? Thankfully balsam fir is pretty easy to climb, so I scaled the tree as quietly as possible and peered in – 3 thrush babies, and pretty old ones too! This nest was close to fledging! But was it a Bicknell’s Thrush nest? It was too high to video, so we instead set up some nets around the nest and tried to catch the parents to confirm that this was indeed a Bicknell’s Thrush nest.

Our first capture that day was one of my favourite field moments ever. It was a colour-banded Bicknell’s Thrush. And low and behold, it was light-green-mauve-black-silver, the same female who nested across the road, about 280m away in the unthinned forest, the year before. I think we had probably only banded 2 or 3 females (they are even more cryptic than males), so it was amazing to see this bird again! She seemed happy and healthy so we released her and left her and her kids alone.

My favorite Bicknell's Thrush, LightGreenMauveBlackSilver

My favorite Bicknell’s Thrush, LightGreenMauveBlackSilver

Colour bands

This bird’s story, and other evidence we collected suggests that Bicknell’s Thrush might be okay in areas with PCT if patches of dense stuff are left for them to use for nesting. It’s an easy way that forest managers can help keep nesting habitat for this species in New Brunswick.

Read our full scientific paper here:

McKinnon, E.A., Askanas, H., and A.W. Diamond. 2014. Nest-Patch Characteristics of Bicknell’s Thrush in Regenerating Clearcuts, and Implications for Precommercial Thinning. Northeastern Naturalist 21(2):259-270.

If you can’t access the full version but want to, tweet me @BirdBiologist or email me, and I’ll send you a pdf!