Friday, September 25, 2009

Where's the jet stream?

In my last post, I blamed the poor fall migration on the position of the jet stream. Fall migration is best following the passage of a low pressure system/cold front, with winds from the north or northwest. Weather systems in North America generally travel from west to east across the continent, with their route guided by winds aloft -- the jet stream. Thus, a nice dip in the jet stream somewhere in the western Great Lakes is most likely to bring the right kind of conditions for birds to move into our area.

My friend Mike McDowell posted some graphics and a nice explanation on his blog last week. Go take a look! His four-panel image comes from, and is updated at least daily. The direct link to the current jet stream position image is here, and as I write this on Friday afternoon, it looks like this:

At long last, the jet stream is beginning to sag south. Although it isn't in the ideal position (such as the example Mike posted), it should help move birds along.

The California Regional Weather Service has a great web site that has all sorts of jet stream images and forecasts, including loops. Use the North America "latest available" link here for a detailed current map. This link goes to an animated loop of a five-day forecast.

These maps and forecasts should be used in conjunction with radar images. The Wisconsin Society for Ornithology has a tutorial on how to understand radar images and so does New Jersey Audubon.

Here are those handy links again:

Fall 2009: Week # 6 in review

Another slow week has gone by. We finally broke 400 new birds banded this week, after 28 days of banding. This time of year, we can expect to band 400 birds in a week. Other folks in the western Great Lakes have also complained about this being a really lousy migration so far. The culprit: the jet stream has for the most part been stubbornly parked at a high latitude, through the middle of central Canada. It's been in this general position since mid-August, a highly unusual situation. Migration is strongly influenced by weather systems, and weather systems are influenced by the jet stream. Rather than going into this here, I'll put some links together in my next post.

We did have a few mildly interesting days. The predominant warbler has been the Blackpoll, followed by Magnolia (below) and Nashville.

This is the time of year when we get very large flocks of blackbirds, mostly Common Grackles and lesser numbers of Red-winged Blackbirds, along with some Brown-headed Cowbirds and (if we're lucky) Rusty Blackbirds. So far, it has only been grackles, and they seem to have arrived/gathered a little early this fall. They mass on the oak trees, ripping off acorns, and carpet the forest floor flipping through the leaf litter. Because of their weight, grackles don't "stick" in the banding nets very well, but it isn't unusual to catch a whole batch of them if they are moving through the net lanes. This is never very fun. They can (do!) pinch quite hard with their sharp bills. They also have very strong feet and it can be uncomfortable if they grab on and get a toenail stuck in your cuticle.

I happen to think that grackles are pretty handsome, but right now they are molting. The one below is a young bird, molting from its dull juvenile plumage into the more typical glossy garb. Judging from the color, this is probably a male. The wing feathers are also molting, or I'd be able to tell which gender by the length of the wing -- males are larger than females.

Speaking of toe nails, here's a robin with pale nails; they are usually dark-colored. We see a number of birds lacking pigment in their nails every season. Often it is Gray Catbirds and robins for some reason.As you'll see in my next post, the jet stream and weather systems are finally on the move. So long as we can avoid rain and wind, things should pick up next week.

Sunday, September 20, 2009

Fall 2009: Week #5 in review

It was another quiet week. There was an influx of migrants on Sep 15, and some obvious large movements of American Robins and Blue Jays beginning on Sep 17. Some new species were recorded this week. Philadelphia Vireos have a very tight fall migration window right around September 15. We saw our first on Sep 12, and banded two on the 15th.

The 16th saw our first White-throated Sparrow of the season, and more were around on Sep 20. Sep 19 we had our first Gray-cheeked Thrush. Cape May Warblers seem to have had a good year. We banded two nice-looking hatching-year males, one of which is shown at the top of the post.
Two older birds were also recaptured this week. The first was a female Northern Cardinal first banded as an adult on April 13, 2003, making her at least 7 years old. We had recaptured her a number of times in 2003 and 2004, but this was the first recapture since then.

Next was a Gray Catbird that had been banded as an adult, in its second year, on May 17, 2005, making this bird at least five years old. We have captured it several times each year, often in breeding condition -- this was a male.
And here's my ID tip of the week (don't get your hopes up that I'll have one weekly!). The bird above is a Chestnut-sided Warbler. Like many (most that I see) individuals of this species in the fall, there isn't any chestnut on the sides. However, the color of the back and top of the head are very distinctive. To me, it's just like the color you get when you use a fluorescent yellow highlighter on newsprint. What do you think?

Sunday, September 13, 2009

How do we know what thrushes are eating?

Last fall, I described the focus of my research: the autumn stopover ecology of migrant thrushes. My paper summarizing weight and fat changes in Hermit, Gray-cheeked (shown above), and Swainson's Thrushes was published earlier this year. This is the third year of building on those results by looking at the specific resources thrushes use here in the fall. Because most migrant birds, including those that typically eat insects, also incorporate fruit into their fall migratory diet, the thrushes make great surrogates for a whole suite of migrant species.

There are lots of fruiting trees, shrubs, and plants on campus. Our banding area, for instance, is located in an area with a high density of Gray Dogwood (Cornus racemosa, below), a native shrub with plentiful white berries.

However, like most urban areas, many of the dominant fruiting plants are from non-native species, such as the Glossy Buckthorn (Frangula alnus) shown below.

As I mentioned previously, some of the questions I seek to answer include which fruiting plants and shrubs commonly found in urban areas -- both native and introduced -- are most important to migratory birds? What is their relative availability? If highly invaded urban natural areas are to undergo restoration efforts, which introduced plants should be left to provide resources for migrant birds while native plants become established?

To find out what the thrushes are eating, we simply collect the droppings they leave in the bags we use to transport the birds from the nets to the banding station. Because fruit passes through birds so quickly (and it is thought that many birds, especially migrants, choose fruit that can be processed quickly and efficiently), we know that whatever they poop out has been eaten on-site. We collect each sample in a plastic bag, labeled with the bird's information.

Later, I sort through and identify all the seeds. I have assembled samples of nearly all the seeds found in fruits growing in the campus natural area (certainly all the common ones). I've also put together a reference book, made up of magnified photos of seeds of dozens of species; these photos are available at the excellent USDA PLANTS database web site. It's actually pretty straightforward. I've had very few seeds I have not been able to identify. I think a lot of them are just malformed seeds of common species. So far, I've collected over 200 seeds from 100 samples from 79 birds (some are from multiple samples from the same bird captured more than once).

In order to determine if resident birds are competing with migrants for the same fruits, or depleting certain fruiting species before migrants arrive, I've started collecting samples from all species of birds, concentrating on American Robins and Gray Catbirds. As we catch WAY more robins and catbirds than thrushes, we will end up with a lot of samples. A UM-D undergraduate and bander, Dana Wloch, will be assisting with the sorting, identification, and compiling of the seed samples as an independent research project this fall. Her time will go to waste, so to speak (sorry, I couldn't resist).

Interested in what I have discovered so far? I'll be presenting an overview of my research and some preliminary seed sampling results at presentations at several bird groups over the winter. The first two are November 2 for Macomb Audubon Society, and November 16 for Grosse Pointe Audubon Society. Check their web sites for locations and times. I'll announce January program dates in a couple months.

Fall 2009: Week #4 in review

I don't have much to say about this week. It was pretty boring. We've had some nice groups of warblers, usually consisting of a dozen species, right behind the EIC. Not many have materialized in the banding nets, however. I think this may be the slowest start to a fall season ever. I've updated the stats in the sidebar, and leave you with a photo of a pair of Black-throated Blue Warblers banded this week. We need some good weather fronts to get things moving, but nothing looks promising over the next 5 days or so.