Life after breeding

I haven't seen an orange-crowned warbler in over a month. Not that that's a bad thing, mind you. I spent 6 months seeing them virtually every day. But I do still wonder what our birds are up to.

The Alaskan birds stopped breeding in July. By that time the days were getting noticeably shorter (we had to use lights at night!) and the food available to them was getting noticeably scarcer (in our insect samples anyways). Their days in the north were numbered, and so they needed to quickly complete the following tasks: (1) raise young to independence (involves continuing to feed them for a few weeks after fledging), (2) undergo a complete molt (involves all of their flight and body feathers), and (3) prepare for the long migration south (involves changes in organ size and considerable fattening). Presumably, by now they would have completed those tasks and are in the process of making their way south, through Canada and towards the southeastern United States - the location where this particular subspecies happens to overwinter. So many tasks with so little time, I wonder how many will make it to the Gulf Coast in one piece.

On the flip side are the Californian birds and, as you might expect, a post-breeding period that is a tad more mellow. Those birds stopped breeding in May and likely hung out on Catalina for a month or two after that. At some point they would have taken off and flown across the 20-some-odd mile channel between the island and the nearby mainland and made their way to an overwintering site in southern California or northern Baja. Not much is known about these birds beyond what takes place during the breeding season, but it is thought that they molt after they reach their winter quarters - an activity that I can only presume they are doing now.

So there you have it, for the birds anyways; now what about me? Well, my southward migration took place on July 25th, taking me from Fairbanks to Anchorage and then from Anchorage to Los Angeles. Jongmin was there to meet me and the next day we set out on our drive back to Colorado. After a brief stop in Las Vegas and a slightly more lengthy stop in Zion National Park (see photo), we were finally back in Ft. Collins.

Now a week into the Fall semester, we are settling into a new, more sedentary routine. Classes, data, proposals, manuscripts - you know the drill. We are also looking ahead to our next field season, which should get underway in February of next year. At that point I plan to continue blogging about our fieldwork; and in the meantime, I'd like to thank anyone who bothered to read about our adventures this year. I hope you will join us again!

In pursuit of The Big One

Alaska is a much sought-after destination. Mere mention of the state conjures up thoughts of vast stretches of untamed wilderness and - at least for me - jagged mountain peaks. Our field site doesn't exactly personify that image of Alaska. We work at the edge of Fairbanks, the second largest city in Alaska, at a site where locals take their dogs for a stroll along the Tanana River. There are no mountains. There are no bears. But there are orange-crowned warblers, and that's all that matters.

All that matters for work, that is. But believe it or not grad students do get to have some fun every once in a while, so when our last nest fledged on July 9th we packed up our camping gear and headed straight for the nearest national park - Denali.

Denali National Park is located within the Alaska Range, a mountain chain that is within view of Fairbanks and is only a 2-hr drive to the south. Established in 1917 as a small reserve, the park has since grown to encompass more than 6 million acres of Alaska's interior (roughly the size of Massachusetts). The centerpiece is of course Mt. McKinley - or, as the locals prefer, Denali, a name that means "The Big One" in the native Athabaskan tongue. We were well-warned before getting there that seeing The Big One was not an easy chore - in fact, the mountain is famous for its cloud-cover and only reveals itself once every 3 days during the summer months. Realizing this, my companions had more reasonable goals in mind: more than anything else, Helen wanted to see a long-tailed jaeger and Jongmin wanted to see a grizzly bear. But I still wanted to see the mountain...

We got to Denali in the late afternoon, arranged our trip at the Wilderness Access Center and proceeded to set up camp at the park's entrance. The next morning we awoke bright and early to catch our bus. You see, Denali is unusual in that there is only one road going into the park and there is limited vehicle access on that road. The result is that everyone has to take shuttle buses to and from their destinations within the park. So on the bus we went.

The first hour was exciting. We saw a fox playing with her pups, a caribou grazing along the river, golden eagles soaring through the sky, and....we saw The Big One. It was in the far-off distance and its base was obscured by neighboring mountains, but the cloudless peak was visible and our bus driver kindly stopped for an "insurance photo" in case the mountain went out of sight. We were thankful. The sky was cloudy and the forecast was calling for more of the same. And indeed, partway down the road the mountain did go out of sight behind a thick layer of clouds.

But the bus ride was still exciting. We spent the remainder of our 5½-hr trip winding our way through the tundra landscape, gawking at the surrounding mountains and keeping watch for our next big wildlife sighting. The highlight was seeing a wolf, but I also enjoyed watching Dall sheep navigate over the rocky terrain and a marmot peering out over the riverbed below.

Eventually we reached our destination and unloaded our gear at the Wonder Lake campground. The location boasts one of the best views of Mt. McKinley within the park – one of the primary reasons we were there - but the clouds were holding tight to that secret, so we went on a hike down to the river and later enjoyed a ranger talk about the gold rush of the early 1900s.

The next morning we hopped on a bus and headed back in the direction we had come the previous day. There are only a handful of hiking trails within the park, and instead of taking one of those visitors are encouraged to forge their own trail. So we asked to be left at a spot that we had deemed interesting on the way into the park and set-out on a hike of our own making. It had rained hard the night before and low-lying clouds hung immediately above us, so we had a dark, wet trek through the alpine tundra. But the plants were brilliant. Small and delicate, with flowers of every hue, we had a great time examining the microcosm below us with each passing step. For the first few hours the only wildlife we saw was a lone caribou. But then we had a flash of excitement in and around our lunch spot. First we spotted a family of willow ptarmigan, then a group of 14 caribou grazing on the hillside above. The caribou seemed uneasy with our presence – moving one way, then another – and then quickly moved down-slope just as a grizzly bear appeared out of the mist above them. While we watched the large bear meander across the hillside, two of the caribou came to graze beside us and a long-tailed jaeger took off and kited in the air above. We had chosen a good hike, it was immediately decided, and continued onward, pleased with our day despite the dreary sky.

That night was our last at Wonder Lake, and our last chance to see The Big One from this prime camping spot. I was disappointed to see a wall of clouds when I opened the tent door the next morning, but – amazingly - holes began to appear in that wall shortly thereafter. The clouds first parted in the distance to reveal a 12,000 ft mountain that was astounding in its own right. But then they began to part on Denali itself, and the neighboring peaks were soon dwarfed by the colossal 20,000 ft mountain rising up from the 2,000 ft valley below. Eventually the whole range was clear and the snow-capped peaks glistened in the morning sunlight. I’ve seen some amazing mountains before – I grew up in the Canadian Rockies, for goodness' sake – but this was something special. It was a view I won’t soon forget.


The rest of our day was spent on the bus, stealing views back at Denali as we made our way towards the park entrance. Our time in the national park was over, but thankfully we still had another day to spend in the Alaska Range. We met up with a couple we knew from Fairbanks – Nathan and Kelly - and set off to the east along the Denali Highway. Our goal on the remainder of our trip was simple: to find an arctic warbler.

An Old World species, arctic warblers are dull in appearance but exciting in migratory habit. From their wintering grounds in southeast Asia, some individuals migrate north to breed in the subarctic forests of Eurasia but others travel all the way across the Bering Straight to breed in western and central Alaska. In June and July they can be found in particularly high abundance along the Denali Highway, so we were excited at the prospect of spotting this unique little bird.

That night we set up camp 30 miles down the road, and the next morning we set out to find our bird. The immediate area did not prove fruitful, so we continued to drive until we reached the Susitna River and its surrounding floodplain. It was there that we saw our arctic warbler. It was small and cryptic, hiding in the dense willow thicket, but we saw it and gleefully added this Old World warbler to our respective life lists.

A fitting end to an incredibly successful trip, we crammed back into Nathan’s truck (our rental car is not permitted on unpaved highways) and proceeded to drive back in the direction of the national park. We picked up our car where we had left it and turned north, out of the mountains and back to our cabin in Fairbanks. Our trip had been a short one - only 5 days long - but was the most time we'd had off in the previous 5 months. A nice reward after a long, tiring field season, all of our goals had been accomplished - Helen with the jaeger, Jongmin with the bear, me with the mountain, and all of us with the arctic warbler. A successful trip indeed!

(Note: if interested, you can scroll down the side panel to see a list of birds spotted during the 2008 field season; visitors of the Smithsonian site will need to click here first, then scroll down.)

Another field season bites the dust

As the remnants of a thunderstorm trickle down upon our cabin and the sun reclaims its dominance in the subarctic sky, I am left to contemplate a field season that is drawing to a close. The past few weeks flew by in an instant. The females arrived in late May and, just over a month later, most have already gone through the nesting process and are in the final stages of raising independent offspring – a time we call the fledgling period. The breeding season is almost over, and the birds will soon begin molting (some already have) and otherwise preparing for the long migration south.


Of course, my thoughts about orange-crowned warblers in Alaska cannot stand alone; they are always with reference to Catalina Island. Our study is a comparative one, and with that in mind I will use the remainder of this post to ramble about the facets of the Alaskan population that interest me most.

Time. These birds are sure in a hurry. They build their nests quickly and – almost literally – place all of their eggs in one basket, with little opportunity for a successful re-nest if they are unlucky enough to lose the predation lottery. That means they have to breed as soon as they get here. That also means that the people who study them don’t have to sit around making bets about which month they will start breeding. Time is of the essence, and these birds don't mess around.

Daylength. Even though the number of days may be limited, the number of hours per day is much less constraining. Sure, the sun dips below the horizon for a few hours each night, but darkness never befalls these birds on their subarctic breeding grounds. As it turns out, this phenomenon affects graduate students and birds in a remarkably similar way: an increase in the number of work-hours and a decrease in the number of sleep-hours. Good thing the breeding season doesn't last long.

Clutch Size. Females lay more eggs in the north than they do in the south. Alaskan clutches typically consist of 5-6 eggs, while Californian ones are much smaller, with 3-4 eggs. Orange-crowned warblers here don't build larger nests, so as the nestlings grow the space they share becomes especially tight. It seems that this is a price the parents are willing to pay to further the odds that their genes will make it to the next generation. Not a bad strategy when you have to survive a journey all the way to the Gulf coast and back before you can breed again.

Food. Theory has it that more food is available during the summer months the further you get from the tropics. I observed a year of complete reproductive failure on Catalina Island last year, so surely I can attest to that. But I have to say that there was less food here than I expected. My fellow graduate students who have been here in previous summers tell me that this year was unusual. We haven't finished processing our insect samples, but our guess is that food abundance was low this year. As someone who is interested in population fluctuations and their affect on higher-levels of the food chain, this little factoid interests me greatly. But at this point I have no idea what would be causing the low insect abundance.

Predation. Warblers here don't have to worry as much about nest predators. The Alaskan climate is too extreme for snakes, but they do still have to contend with foes of the avian and mammalian variety - namely, jays, magpies, mice, and voles. Still, in the end the predation rate is lower - a nice reward for migrating all the way to a site with such a short breeding season.

Density. Birds in Alaska range over a much larger area than their southern counterparts. On Catalina, the birds are so packed that you can walk 20 m from one nest to another, but here a few hundred meters can separate the core of neighboring territories. In all likelihood, this has something to do with migration strategy. Adults here incur much higher rates of mortality during the non-breeding season, which limits the number that make it back to breed each year and in turn how densely packed they are on the landscape. For the birds this means that they have fewer neighbors to compete with, and for us this means that we have to survey a much larger area than on Catalina.

In the end, orange-crowned warblers at the two extremes of their breeding range are more alike than they are different - for example, in their reliance on leaf-gleaning for acquiring food - but to us it is the differences that are the most interesting. Warblers here are not the same as warblers in California. Geography matters. These are things I can attest to after five months following the same species through the cactus patches of Catalina Island and the marshes of central Alaska - a long and exhausting field season, but also a rewarding one.

The forgotten island

So whatever happened to Catalina, you may ask? The last you, as a reader, heard was that the birds were double brooding and the migrants were passing through. Not to worry. We did not abandon that island entirely. Luckily one of our field assistants was able and had the desire to stick around and monitor our remaining nests. As it turned out, only two of the double-brood nests were successful and the rest were lost to predators. Sad maybe, but also very useful information for us as we are interested in per capita rates of reproductive output. The end result of the Catalina field season was that the average pair of warblers was able to raise 3 young to the point of fledging. Much better than last year, when we did not document any fledglings on the island!

If you read my previous posts, you may remember that very few nests were lost to predators in the first round of breeding. You may also remember that snakes were implicated as the primary nest predator on Catalina Island. So why the sudden increase in predation later in the season? Well, one possible explanation is that snake activity increased from the month of March to the month of May. Ectotherms like snakes rely on warm temperatures to heat their body and enable forays in search of food. As the breeding season progressed and the days became warmer, it is likely that snakes were moving across the landscape faster and more frequently - and, as a result, encountering more and more warbler nests.

If you amass hours and hours of nest videos, eventually you are bound to catch a predation event in action. Earlier in the season we caught a california kingsnake taking nestlings out of a nest, but the video was from too far a distance to be interesting beyond simple documentation of the event. But I am pleased to report that Dan (the field assistant who remained on Catalina) got some great footage of one of our last nests being discovered and subsequently depredated by a kingsnake. The nestlings were 7 days-old at the time, and as you will see in the video clips below they made quite the meal for the relatively-small snake. Enjoy!

Clip 1: The discovery


Clip 2: The meal

My northward migration

It has been nearly a month now since I arrived in Alaska. I said my goodbyes to the Catalina field site on May 14th, caught a ride into town bright and early the following morning, and left the island for the first time in exactly three months. Talk about culture shock. The traffic and smog of LA and the hordes of unfamiliar people contrasted starkly with the small community where I had been living in the rugged interior of Catalina Island. But I survived. A shuttle quickly whisked me from the ferry terminal at Long Beach to the airport terminal at LAX, and soon I was onboard a flight bound for Seattle. The plane took off to the west and, in a fitting departure from California, it flew up the coastline in such a way that I had an excellent view of Catalina and most of the other Channel Islands (see photo of Anacapa and Santa Cruz). It was official: I was headed north, leaving behind our southern birds to catch up with their boreal-breeding counterparts.

My northward migration was of much shorter duration than would have been the case for the birds. I had a 3-hr flight to Seattle, a 3.5-hr flight to Anchorage, and a 1-hr flight to Fairbanks. In Anchorage I met up with Jongmin and Brent, who had arrived on separate flights, and was quickly reminded of my new location in the far north. Standing in the airport terminal not 5 meters from us was Jeff Corwin, a popular television personality from Animal Planet. We learned that he had just returned from a stint of collaring polar bears further north. I can only presume that his trip had something to do with the then days-old news that polar bears were being listed as a threatened species in the US. Regardless, there he stood in front of us. Not bad for a first impression of Alaska.

Our plane touched down in Fairbanks in the wee hours of the morning and there to meet us was Helen, who had arrived a few days earlier. She drove our dreary-selves back to the cabin where we were to stay, and there we crashed after our long day of traveling. We awoke the next morning and, after having skipped one day of fieldwork, I found myself strapping on my hiking boots and harnessing my binoculars around my neck. The first day was easy: we got a tour of the study plot, checked out some singing males, and paid a visit to an active bald eagle nest. The females were still on their migratory journey so that left us with time to settle in and adjust to our new surroundings.

But the calm period did not last long. Jongmin spotted our first female on May 18th, a bird carrying black, pink and orange leg bands that had been given to her the previous year. She took a few days to recuperate from her series of flights north and began building a nest on May 22nd. The females that arrived in the days and weeks to follow quickly followed suit, keeping us on our toes.

We have done well so far, with 29 nests and counting. The earliest are on the verge of hatching and the latest are still lacking a complete clutch of eggs. They are not easy to find. Orange-crowned warblers here nest exclusively on the ground, and the females are skittish if they notice us anywhere in the vicinity of their nests. It is therefore of the utmost importance to hide ones-self in the bushes to find the exact nest location for a building female, a feat of concentration when faced with a swarm of hungry mosquitoes.

We are now bracing for the upcoming nestling period when we will be running around video-taping nests and measuring nestlings, not to mention trying to find the nests we have missed. I will try to post in the weeks to follow but I cannot make any promises! In the meantime, I will leave you with this photo of a busy beaver and you can think of us.

North they go

It is that time of year again. Across the northern hemisphere the poleward procession of the snow-line is giving way to a swarm of migratory birds. We are reminded of that fact every time we see a bird, or hear a sound, that seems out of place. Migrants have been passing through Catalina since mid-April and have been doing so in waves. We had one such wave today, bringing with it Townsend's Warblers, Hermit Warblers, Black-throated Gray Warblers, Western Tanagers, and plenty of other species that I'm sure we missed. Over the years we have caught many of those migrants and, before releasing them unharmed, have had them pose for a few photos.

Hermit Warbler

Warbling Vireo

Townsend's Warbler

Wilson's Warbler

Orange-crowned Warbler

Ok, so I know what astute readers out there must be thinking: "Aren't you there studying a breeding population of orange-crowned warblers? Why is that last photo lumped in with the other migrants?" Well, believe it or not - on this same day last year - we caught a few orange-crowned warblers of the Alaskan/Canadian race that were migrating through Catalina (the above bird is smaller and has duller plumage than our local breeders). We don't know where those birds ended up, but they do serve to highlight just how delayed the northern breeders are. Here most orange-crowned warblers have raised a batch of young (i.e. a brood) by early May, but the Alaskan birds have just started to make their way north. In a few short weeks we will catch up with some of those birds in Fairbanks, and will start studying them just as their migratory journey ends and their breeding season begins. Until then, we will continue to enjoy the passing of migrants on Catalina Island.

To breed or not to breed?

Wow, it sure has been a while since I last posted to this blog! Sorry to anyone who was anxiously awaiting news of the warblers on Catalina Island. Assuming such a person exists, I can only imagine they had two options running through their head while pondering my post-less blog for the past two months: (1) the birds aren't breeding (again) and she has nothing to write about, or (2) the birds are breeding and she is just too darn busy. If you chose option number 2 - ding ding ding - you are correct. The birds did breed and we have a mountain of data to show for it.

We started the field season wondering when the birds would breed. Last year, after the driest winter on record, only a few of them did and we had to wait until mid-April to see that happen. But this year the island received a few inches of rain in the months that preceded our arrival, and some key storms in late February led to an immediate greening-up of our study site (see photo above). The oaks leafed-out and the birds quickly followed suit, building nests, laying eggs, and providing us with an actual breeding season as opposed to last year. Needless to say that made us happy, and busy at the same time!

I am used to migratory birds, where some birds arrive, you find their nests, and then other birds arrive, and you find their nests. But in this system the birds over-winter on the Channel Islands and the nearby mainland, so they had come to Catalina and had established territories weeks, if not months, in advance of the initiation of nesting activities. So when the environmental conditions were right, they all starting building nests at once! At one point it seemed like there were building females everywhere I looked.

The incredible synchrony that we observed this year was unusual compared to previous years, and created a situation that kept us on our toes for the next few weeks. We found most of our nests during the incubation period, either by following chipping females or by flushing them off their nests. This was a busy time, as we had many nests to find and only 4 of us on the ground trying to find them. Once we found a nest we had to carefully check it every 2 days to see if the eggs had hatched, and to monitor whether it was still or active or had been found by a nest predator.

On Catalina, there are quite a few nest predators in the form of snakes, foxes, mice, and other creatures. But the ones that seem most troublesome from the warblers' perspective are the snakes. For instance, so far this year we have positively identified two predators eating warbler young and both were of the reptilian variety - one a gopher snake and the other a california kingsnake. We started seeing snakes early this year. I spotted my first rattlesnake on March 9th (see photo) and proceeded to see many more in the ensuing weeks (one of which was far too close for comfort). This, after having gone an entire season without seeing a rattlesnake last year. Despite this, the birds had an exceptionally low rate of nest predation this year. Only a few of our nests were eaten in the month of March, and only in the past few weeks have predators been apt enough to find our warbler nests.

Lucky for the birds, and lucky for us. One of the things we are interested in is parental feeding behavior, and we study this by setting up a small pin-hole camera at nests and recording for an entire 24-hour period. But we can only do this if the nestlings survive long enough to be 6 days old. This year, many of them did and we were left running around video-taping nests and, on the following day, taking nestlings out briefly to weigh and measure them.

Through all this we had help from many people. In addition to Jongmin and myself, we had two field assistants actively searching and monitoring warbler nests. We were also fortunate to have our advisors - Drs. Cameron Ghalambor and Scott Sillett - visit in early March, a postdoc - Dr. Brent Horton - visit two times in March and April, and a labmate who is working on Santa Cruz Island - Helen Sofaer - visit in April. They helped to identify birds, to capture and band them, and of course to find their nests. It was truly a team effort.


So what are we up to now, you may ask? Well, believe it or not some of the birds are going a second round. They bred early, experienced an exceptionally high level of nest success, and still have the time (and food) needed to raise another batch of young. So they are giving it a shot at least. But it remains to be seen how successful this attempt will be. The predators seem to be picking up steam in terms of their nest-finding ability, so we are not expecting an incredibly synchronous (or busy) nestling period this time around. Stay tuned to find out!