Movement Ecology of Animals

Homepage of Dr. Emily A. McKinnon


Leave a comment

Year of the (female) Bird Biologists

I am so excited that Audubon, BirdLife International, Cornell Lab of O, and National Geographic have banded together and decided that 2018 is the ‘Year of the Bird’. This means extra special birdy events going on all year, and extra special attention to the organisms that have fascinated me for the last 10+ years (ahem, every year is year of the bird for this family of ornithologists).

This kind of publicity is what birds need right now; they are the proverbial canaries warning of problems with our planet. Altering their timing of migration in response to climate change, singing a different song to be heard over city noise, accumulating toxic chemicals while breeding in the seemingly pristine Arctic

Birds are telling us that we are impacting our planet with our fossil fuel addiction, rapidly increasing urbanization, and rampant use of chemicals. But birds also tell us about resilience, about facing an entire ocean with no land in sight and launching into the air, landing days later at a tropical destination.

We all need to pay more attention to birds.

As a subscriber of National Geographic I was excited for the special Year of the Bird feature articles. And for March, a whole article on bird migration! My own personal research subject and, in my mind, one of the most mind-blowing behaviours that birds pull off, season after season. The issue even came with a migration poster! Score!

The article describes the epic migrations of godwits, amazing work on migration timing by postdoc Dr. Jesse Conklin and colleagues. The author speaks with Dr. Ben Winger, expert in biogeography and evolution of migration, about the origins of migratory behaviour. Peter Berthold, who has literally written the book on controls of migration is also interviewed to describe how migration might have evolved as climate in sub-saharan Africa changed over millennia. Henrik Mouritsen, Martin Wikelski, Pete Marra– all ornithologists whose work I have studied over the years.

However, the more I read this article, the more I had the nagging feeling that something was missing.

Where are all the female bird biologists?

I know there is a bias in Science where females are still underrepresented. But I always felt that in my field, behavioural ecology of birds, the problem wasn’t as bad, as say, in Math and Engineering (in Canada, anyway, there were actually more women university graduates in general sciences than men). So my impression was (and still is) that there are plenty of amazing female scientists studying birds and migration behaviour.

Therefore I was surprised that out of all the researchers (both early career postdocs and senior scientists) mentioned in this Nat Geo article (n = 18, not including Andrew Farnsworth who consulted on the infographic figure), only 2 are women, and both were mentioned in the context of a team (Bob Gill & Lee Tibbetts of USGS, and Wolfgang & Roswitha Wiltschko of Goethe University in Frankfurt).

Anyway, I thought I would flesh out the article with some of the amazing work by female ornithologists that I know of who have taken the field of migration ecology forward.

Two caveats: 1) This is not an exhaustive list – just a few names that would have fit nicely into the theme of Nat Geo’s original article, and 2) This is not to detract at all from the work of the amazing ornithologists interviewed/featured in the article already. Male ornithologists are awesome too. I should know, I’m married to one (Kevin Fraser).

Click the names to see webpages and links to papers by these folks:

Susanne Åkesson

It’s pretty nutty that godwits can fly from Alaska all the way to New Zealand – 8 days of non-stop flapping! Makes me tired just thinking about it. But Dr. Susanne Åkesson’s Common Swifts are possibly even more amazing – her team has shown, by using tracking devices equipped with accelerometers – that the swifts don’t land for the entire winter while they are in Africa. If that doesn’t blow your socks off, I don’t know what will. She has done an incredible amount of work on migration for the last 20+ years, looking at proximate drivers of navigation and orientation in songbirds and shorebirds.

Debra Arlt

Wheatears have some of the most amazing migrations of all songbirds. From Canadian Arctic eastward to Africa? No problem. From Alaska to Africa (the long way – westward) – also no problem. Debra Arlt has been using the differential migrations of populations of wheatears to explore stopover biology as well as the effects of tags on fitness of the birds.

Melissa Bowlin

I love the story of Bill Cochran and Martin Wikelski chasing down their radio-tagged Swainson’s Thrushes (pre-geolocators, pre-Motus) all night, trying to figure out the proximate rules for songbird migration. Dr. Melissa Bowlin has continued this amazing work, and shown how wing shape in thrushes affects aerodynamics of flight, among other things. She continues to use the chase-car strategy to look at flight patterns in migrating thrushes, and has discovered some crazy patterns in flight altitude that are still a mystery.

Kira Delmore

It’s really interesting to think about how long-distance migration might have evolved, and Ben Winger has done some really neat stuff looking at origins of migration (i.e. the southern vs. northern home theories). One researcher I think of when it comes to evolution of migration patterns is Dr. Kira Delmore (postdoc at Max Planck). She did a great study using geolocators on Swainson’s Thrushes in a hybrid zone between western and eastern subspecies, and she found that the hybrid individuals had a sub-optimal migration route compared to both parental types. Migration as a post-zygotic barrier to (sub)species fusion! How awesome is that. She continues to explore genetics (and epigenetics!) and migration behaviour in a search for the genetic basis for migration.

 

Camila Gomez

While working on her PhD in Colombia at the University of the Andes, Ms. Gomez has produced some rock-solid research on stopover biology of thrushes. Along with colleagues working at a stopover site in northern Colombia, she has shown that thrushes have the fuel to make it all the way to their breeding sites in a single mega-flight. To me, her work is starting to tip the scales in terms of how we think about songbird migration – we thought most used a short-hop strategy, stopping frequently to refuel – however, Ms. Gomez’s work and others is starting to point to a more shorebird-like long-jump strategy. I suspect there will be more amazing discoveries in the future that will add to this picture.

Elizabeth Gow

A Stutchbury alumna (see Bridget below), Dr. Gow has studied the differential migrations of male and female woodpeckers. That is, after she figured out how to get them to stop ripping off the light stalks from the geolocators! #woodpeckerfieldworkproblems She is now working on a huge migration dataset for tree swallows as a postdoc in the Norris lab.

Yolanda Morbey

Dr. Morbey has done some nice work on timing of migration, especially protandry – the idea that males arrive at breeding sites before females- with both theoretical and field-based studies.

Rachel Muheim

Another female ornithologist who has really explored bird navigation systems is Dr. Rachel Muheim. Both in the field and the lab, in well-designed experiments, she has studied the magnetic compass systems that birds use to figure out where to go when they migrate.

Janne Owehand

Dr. Owehand is an up-and-coming bird biologist who I first met in Latvia at the EOU in 2011. Her PhD work resulted in some amazing papers exploring constraints on long-distance migrations of Pied Flycatchers. I will forgive her early papers on earthworms and bats because her PhD work is just so cool. J If you want to know more, check out her TEDx talk: https://www.youtube.com/watch?v=hUQeE4Hr3qA

Bridget Stutchbury

Full disclosure, Bridget was my PhD advisor, but the reason I wanted to work with her was the game-changing Science paper showing the first geolocator-based migration tracks from Wood Thrushes and Purple Martins. Bridget didn’t really start off as a migration ecologist but her behavioural ecology background and strong interest in conservation of songbirds led her directly to the tracking work that caught my eye. She has been exploring migration as it relates to conservation of songbirds for the past 10 years, and is now doing some really interesting work with another rockstar bird biologist, Dr. Christy Morrissey, on how pesticides affect songbird migration.

 

***

These are just a few of the amazing researchers that I know of whose work would have fit well into the Nat Geo article. There are lots more awesome bird biologists (who just happen to be female) that are studying aspects of bird migration more generally, e.g. Emily Cohen, Hanna Kokko, Jen Owen, Kristina Paxton, Jill Deppe, Kristen Covino, okay somebody stop me!  In the ornithology textbooks of the future, I’m sure you will see their work highlighted for the important contributions they and many others are making to the field. In fact, I just might have to go write that textbook myself to make sure it’s done right!

Advertisements


3 Comments

Winter sex-segregation of Snow Buntings explained: The boys are just bigger

Today I’m going to write about one of my new study species, the Snow Bunting! For those of you sweltering through some hot buggy fieldwork at the moment, hopefully this reminder of windswept and snowy fields will help temporarily cool your thoughts.

Beautiful Snow Buntings in Quebec by Jean/Ange (https://www.flickr.com/people/anjoudiscus/)

Beautiful Snow Buntings in Quebec by Jean/Ange (https://www.flickr.com/people/anjoudiscus/)

I have the privilege of working with some amazing data collected by Citizen Scientists across Canada (and some in the US too) on the most northern-breeding Passerine bird, the Snow Bunting! Amazingly, there are keen folks who like going outside in frigid temperatures and patiently baiting open snowy fields with cracked corn or millet for Snow Buntings during the winter months when these little songbirds are found in southern Canada and the northern US. These stalwart volunteers form the Canadian Snow Bunting Banding Network (CSBN). Once the buntings are baited, they are trapped with ground walk-in style traps. Basically, the birds walk in, and can’t fly out. There are some great YouTube clips of  Snow Bunting trapping. Once captured, volunteer banders can measure, weigh, and band each bird, making note of its sex and age before releasing it to its flock. Some sites have amazing catching success and trap and band literally thousands of buntings per winter!

David Lamble, member of the Canadian Snow Bunting Banding Network, checking a walk-in trap.

David Lamble, member of the Canadian Snow Bunting Banding Network, checking a walk-in trap.

I think part of the reason why you find people willing to brave the wind and snow is that these are some of the most endearing songbirds around.  Nick-named ‘snowflakes’ for their behaviour of flying in twittering flocks over snow-covered fields, Snow Buntings are a cheerful sight and sound on any dull winter day. Plus it’s pretty darn amazing that a 35-gram bird is even out there at all, seemingly content even with -40C nights a regular occurrence. One particularly talented Snow-Bunting aficionado is Marie-Pier LaPlante (also doing her Masters research on Snow Bunting flocking behaviour), who wrote a song about them! Listen to it here: 

So all of this winter banding has generated some pretty neat data on winter distributions of this species. One obvious pattern is that there seems to be a sex-bias in captures at some sites. For example, in Thunder Bay, Ontario, mostly males are captured. In Essex County (southern Ontario), mostly females are captured. My colleague Christie Macdonald wanted to figure out what was explaining this pattern for part of her Masters thesis at the University of Windsor in Dr. Oliver Love’s lab. She hypothesized three possible explanations for this pattern: 1) Males are more cold-tolerant because they tend to be a bit bigger, 2) Males winter closer to their breeding sites so they can get back earlier to claim nesting sites, and 3) Males winter in the ‘best’ habitats and kick females out through social dominance, resulting in an overall sex-biased distribution. In short, we call these: 1) the body size, 2) arrival time, and 3) social dominance hypotheses.

Each dot shows a banding site and the size of the pie shows the number of birds captured. You can see there is a gradient with more females captured in southern Ontario - but there are some exceptions, i.e. in Newfoundland, there are quite a lot of females captured despite it being very far north.

Each dot shows a banding site and the size of the pie shows the number of birds captured. You can see there is a gradient with more females captured in southern Ontario – but there are some exceptions, e.g. in Newfoundland, there are quite a lot of females captured despite it being very far north.

We set out to test these hypotheses using our ginormous banding dataset of nearly 40,000 winter site captures (whoa) combined with migration information from directly tracking 19 of these little guys with geolocator backpacks.

We looked at the ratio of males to females at each wintering site and compared it to the local weather patterns. Since males are bigger, they should be more cold-tolerant, so we predicted more males and bigger birds of both sexes at colder and snowier winter sites. If males were wintering north of females to get back earlier at breeding sites, we predicted they would have shorter spring migration distance. The trickiest hypothesis to test was the social dominance hypothesis, but we figured out a roundabout way to look at it. Basically we went on the premise that birds with less access to food tend to carry more fat as insurance against starvation. So we predicted that if females are being denied access to food by males, they might carry more fat than males, regardless of size or local weather. We had fat scores (relative measures of subcutaneous fat) from a lot of our captures, so we used these measures to test for patterns in female fat levels that could indicate they were being excluded from food.

The first thing we found was that sex ratio didn’t seem to change much over the course of the winter at any given site. Then we looked at the size of birds relative to weather. We used data on average snow depth, snowfall and temperature, and combined them into one measure of weather harshness using a principle components analysis (PCA). This gave us a measure called PC1weather, where higher values = more ‘wintery’ sites. We found that there was a significant relationship between body size (measured by wing length) and weather – bigger birds of both sexes were found at colder sites! Also we found that the proportion of males was related to the weather in the same way. Proportionally more males were captured at more wintery sites.

Males are always bigger than females, and older birds are always bigger than first-winter birds, but the biggest birds in each age-sex group were found at colder sites (higher values of PC1 weather = more snowfall, deeper snow on the ground and colder temps).

Males are always bigger than females, and older birds are always bigger than first-winter birds, but the biggest birds in each age-sex group were found at colder sites (higher values of PC1 weather = more snowfall, deeper snow on the ground and colder temps).

Higher proportions of males were captured at sites with harsher weather (higher values of PC1weather indicate more snow on the ground, greater average snow fall, and colder temps).

Higher proportions of males were captured at sites with harsher weather (higher values of PC1weather indicate more snow on the ground, greater average snow fall, and colder temps).

So it looks like we are getting lots of support for the body size hypothesis – namely, the bigger you are, the more you can tough it out when the weather is harsh. Because males tend to be bigger than females, this explains why there tends to be more males captured at more northern sites – those sites tend to be the coldest and snowiest.

But males also need to get back to their Arctic-breeding sites early, so maybe that is also driving their choice of wintering site. When we looked at our 19 birds tracked on migration from a breeding site at East Bay Island, in the Canadian low Arctic, we found that males didn’t migrate shorter distances in spring than females. There was a slight trend for males to winter further north but this only translated into ~150km difference on spring migration. Hardly enough to allow males to arrive much earlier at the breeding site (we know buntings can easily cover 150km of migration in a day from Christie’s previous geolocator study). Therefore we concluded that the arrival time hypothesis wasn’t the main reason behind the differential distribution of buntings by sex in winter.

Here's one of our backpack-toting Buntings from East Bay Island

Here’s one of our backpack-toting Buntings from East Bay Island.

Males didn't really winter that much close to their breeding sites than females. Overall spring migration differences were negligible.

Males didn’t really winter that much close to their breeding sites than females. Overall spring migration differences were negligible.

Finally, we tested to see if female buntings carried more fat than males, possibly indicating that they had less access to food via social dominance effects. While our fat-score models were generally pretty poor, we found a trend that females did tend to carry more fat than males, independent of weather effects on fat levels. Older birds also tended to carry more fat that younger birds, which seemed weird at first, since older birds are usually the dominant ones in most species I’ve studied. But, delving into some of the Snow Bunting literature I found a study on dominance in flocks of buntings wintering in Scotland that showed younger birds are actually dominant over adults (Smith and Metcalfe 1997)! So the fat scores do make sense with what we know about dominance status.

At the end of the day, the best answer for why do male snow buntings winter further north than females seems to be that the males are simply bigger, and presumably better able to tolerate those 30-cm dumps of snow and -40C nights. One interesting implication of this relates to climate change. Winters in North America are getting warmer, and less snow will become the norm in may places (Krasting et al. 2013 Journal of Climate). Will this reduce constraints on smaller-bodied female buntings in future? Migrating farther distances from breeding sites is presumably costly, so if they don’t need to go far to find tolerable winter sites, perhaps they will end up wintering further north. Time will tell, and maybe our winter distribution map will have a lot more pink on it in decades to come.

For our full paper, please visit the Journal of Avian biology link below or email/tweet me for a copy:

Macdonald, C.A., McKinnon, E.A., Gilchrist, H.G., Love, O.P. 2015. Cold-tolerance, and not earlier arrival on breeding grounds, explains why males winter further north in an Arctic-breeding songbird. Journal of Avian Biology (accepted). DOI: 10.1111/jav.00689


4 Comments

Jungle life is not always easy for Wood Thrushes

Whenever I tell people that I did my PhD research in the tropical forests of Belize, they tend to roll their eyes and comment sarcastically on how hard that must have been to handle…warm tropical breezes, beautiful beaches, fresh papayas, and cold Belikin beers…

Although I’m not complaining, let me just point out that it ain’t always easy living in the tropics! Yes it’s hotter than Canada in January, but I also got debilitating heat rash from the 35C+ and humidity, leaving me with blistered hands and face. Not fun. Yes, there are awesome tropical fruits (not just papayas! molly apples, soursop, custard apple, pineapple, mango, surinam cherries) and in general the food is delicious (I actually love rice and beans). But there’s always a chance of good ol’ Montezuma’s revenge given all the new fauna that get introduced to your digestive system! I won’t even get into the botflies, ticks, botlass flies, deer flies, sandflies, kissing bugs, scorpions, tarantulas… you get the idea. It’s not all beers on the beach. This is why I never got a tan.

Okay, I admit there were some beers on the beach!

Okay, I admit there were some beers on the beach!

And I figured out during my PhD that, likewise, it’s not just easy living for the migratory Wood Thrushes that make the jungle their home.

I went to Belize to figure out what was important to Wood Thrushes during the non-breeding season (and also how that influenced their migration; but that’s another paper and blog post). Wood Thrushes like forests, and they eat both arthropods (insects, spiders) and fruit. Previous work on the fruit-fly of the migratory bird world, the American Redstart, showed pretty clearly that habitat moisture levels (i.e. rainfall) are the major limiting factor for their success in winter. When it gets dry, insect abundance declines and insect-eating birds have to work harder to get through their day. Plus there’s a seasonal change – the tropics, at least in Central America and the Caribbean, tend to dry out from October to April, over the course of the wintering period for migratory birds. So the environment gets increasingly hostile for an insectivorous bird. Couple this with the fact that they have to power a migration of several thousand kilometres and you can see that late winter is really crunch time for migratory songbirds.

Now this has been shown for redstarts, and also Ovenbirds and Northern Waterthrush. The picture for Wood Thrushes was a little less clear. Unlike their smaller warblers cousins, Wood Thrushes are big chunky birds perhaps less prone to suffering effects of habitat dryness. Plus they can also eat fruit, so if arthropod abundance goes down, maybe they can compensate by gorging on some tropical figs. The other factor is that Wood Thrushes are forest-dependent birds. Unlike the redstarts, which can be found in really dry scrub habitats, Wood Thrushes tend to hang out in more shady, moist areas overall. So is rainfall still a major limiting factor for Wood Thrushes?  Part of my PhD was trying to answer this question.

I wanted to capture the seasonal variation in habitat quality for Wood Thrushes, so I spread out my field work over their entire wintering period  – spanning late October to early April. Over this time, I captured Wood Thrushes and measured their weight, fat levels, muscle levels, as well as their hematocrit (packed red blood cells). I also collected arthropods in pit-fall traps and surveyed for fruit along transects to get an idea of how much food was around at different times of the season and in different habitats. Finally I measured soil moisture levels to get a sense of how dry things were getting.

Collecting a small blood sample from a Wood Thrush. We used this to measure hematocrit, diet, and we used  the DNA to determine sex.

Collecting a small blood sample from a Wood Thrush. We used this to measure hematocrit, diet, and we used the DNA to determine sex.

We dug pitfall traps with old machetes and emptied them daily for 3 days in each location.

We dug pitfall traps with old machetes and emptied them daily for 3 days in each location.

So here’s how the story goes, at least in terms of the habitat. The forest starts off really wet (and anecdotally, full of mosquitos!) and steadily dries out from October to April. Parallel to this decline in moisture there is a decline in arthropod abundance, as you might expect. Bugs don’t like hot and dry, so they either leave, die, or hide when the conditions get rough. I also found (kind of surprisingly) that the fruit abundance is also lower as the season progresses. Hmmm, not looking good for the Wood Thrushes. Less food, more hot and dry, plus they have spring migration looming on the horizon…

Here’s how the story goes for the birds: they start off fat, heavy, with big muscles, and they consistently get lighter, carry less fat and tend more towards emaciated muscle levels! Yikes! Packed red blood cells didn’t change, although you might expect higher levels of red bloods cells in preparation of the marathon of spring migration (like blood-doping athletes, birds with more red blood cells can migrate more efficiently). So it really is crunch time for Wood Thrushes at the end of their overwintering period!

Wood thrush body condition (a) was lower in the dry season, (b) hematocrit was the same, and (c) fat and (d) muscle scores declined. The three habitat types showed basically the same pattern, even though the scrub-forest tended to be  bit drier.

Wood thrush body condition (a) was lower in the dry season, (b) hematocrit was the same, and (c) fat and (d) muscle scores declined. The three habitat types showed basically the same pattern, even though the scrub-forest tended to be a bit drier.

So what does this mean? I think it tells us that Wood Thrushes may be more similar to redstarts than we thought, in that big-scale processes like seasonal drying have the capability to affect their body condition in a big way. Eating fruit or living in a forest didn’t seem to provide any buffer from this seasonal change (although I have data that indicates they aren’t actually eating a heck of a lot of fruit – paper coming soon). I suspect that Wood Thrushes are still able to migrate northwards even if they do decline in condition over the winter- but what effects might this have on their survival or reproductive success?

Another factor to consider is that Belize, like most of Central America, is already experiencing the effects of climate change. Just in the last 20 years or so, the dry season mean temperatures have increased by about 0.5C. And climate projections indicate more warming (and increased frequency of droughts) in the future. Maybe Wood Thrushes are already suffering the effects of hotter, drier, wintering sites. Add in high rates of tropical deforestation and it’s no wonder that the Wood Thrush is listed as a Threatened species in Canada.

So what do we do? Unfortunately climate change doesn’t seem to be going away anytime soon, but I think in the short term, protecting remaining tropical habitat for Wood Thrushes would be helpful. The more fragmented a forest is, the more it dries out, exacerbating the overall seasonal drying. As scientists I think it will be important to look at the climate projections and assess which regions are going to getting hotter and drier faster, to assess where Wood Thrushes and other species may be more affected by these changes. And of course, by buying delicious Bird-Friendly Coffee we can support farmers who create cool shady coffee plantations where Wood Thrushes can find lots of arthropods!

Read my full paper on winter ecology of Wood Thrushes here (or email me for a copy if you don’t have access to Oecologia):

McKinnon, E.A., Rotenberg, J. A., and B.J. M. Stutchbury. 2015. Seasonal change in tropical habitat quality and body condition for a declining migratory songbird. Oecologia Early Online. 10.1007/s00442-015-3343-1