Bird Migration Forecast

A cooperative effort between Cornell Lab of Ornithology and Oregon State University last fall, using a grant from the Nation Science Foundation, created BirdCast. What is BirdCast?

BirdCast is nothing other than a bird migration forecast!

That's right! We now have national weather and its resulting affects upon bird migration. The link in the paragraph above actually goes to the first forecast of this season, predicting a strong migration today and tomorrow in the Great Plains. But that's not all!

This bird migration forecast also tells the predicted species that will be migrating!

Now you can go to bed in the evening and know whether or not you should set your alarm early in the morning to visit your local migration hotspot!

Greg Haworth over at Birds over Portland has been posting radar images of bird migration. His last entry was in October, and he hasn't started yet this spring. I sure hope he is able to compare the BirdCast forecast with actual radar images this spring. It seems that migration in the West is not as dramatic as that in the East. For one, our migrants can fly over land all the way here. Most birds in the East migrate over the Caribbean and can't just set down when winds turn unfavorably on them.

What makes Mount Tabor such a good place for migration?

Dusky Flycatcher, a rare spring migrant west of the Cascades, Mount Tabor, Portland, Oregon, 7 May 2011 by Greg Gillson.

 

Yesterday I talked about Mount Tabor park in Portland, Oregon. I asked: "What makes Mount Tabor so good for Neotropical migrants? When is the best time to visit?"

The information here applies specifically to spring migration in the lower valleys west of the Cascades in the Pacific Northwest. But it also applies more generally to the entire the West Coast.

The insectivorous Neotropical migrants that breed in or migrate through the Pacific NW--warblers, vireos, tanagers, orioles, buntings, grosbeaks, flycatchers, and others--winter in western Mexico or central America. As days become longer and spring arrives, with trees leafing out and insects hatching, bird migration begins.

The first migrants arrive in mid-April (swallows by April 1), but many do not arrive until early May--each species is different (and predictable). Migration is usually over by the first week of June. In most species, adult males arrive first, adult females a few days later, and first-year birds (hatched last year) often a bit later.

Birds migrate first through the warmer lowlands, then move north or upslope as it becomes warmer. So, for instance, migrants may appear on the coast first, western valleys next, east of the Cascades later, and the mountains lastly. In years with heavy snow pack, mountain breeders may remain unseasonably late in nearby lowland areas (into June).

In general, a species of bird will arrive in Eugene, Oregon a week before Portland. Then a week later they arrive in Seattle. It seems there are always a few scouts--individual birds well in advance of the main movement. Finding these first of year (FOY) migrants is a fun challenge for many birders.

These birds migrate primarily at night. They don't want to fly into strong headwinds, thus wait for winds from the south. In the Pacific NW, that means unsettled weather in spring. Clear skies in spring are accompanied most often by cold winds from the north, impeding migration.

If a cold front is over you at dawn, all migration will stop at this front--you'll have an incredible "fall out" of migrants. So, wise birders watch the weather and weather maps in spring.

Migration proceeds in "waves" as the weather promotes or impedes migration.

But why is the city park of Mount Tabor so good for migrants?

Mount Tabor's top is just over 600 feet elevation. This old volcanic cone, now covered in trees, rises sharply 400 feet higher than the surrounding city of Portland. When dawn ascends, migrating birds over the industrial, commercial, residential landscape of Portland see the green slopes of Mount Tabor and land there. It is an island effect.

As the sun hits the eastern part of the mount first, insects wake up and warm up there first. As the warm air rises, insects move upslope. So migrant bird activity is often most observed first on the east and southern exposures near the top of such hills where the tired and hungry birds have a needed food source. In order to see birds best, it helps to have openings, such as a clearing or parking lot near the top of such hills.

So, what time of day are we talking about? Soon after dawn. In early May, arrive by 7 am on cloudy days, earlier if sunny. By 9:00 am, activity may be over. Birds have eaten, so they sleep the rest of the day away, preparing for the next night's migration to continue on their journey.

A visit to Mount Tabor, Portland, Oregon

Birders enjoying spring migration on Mount Tabor, Portland, Oregon, 7 May 2011 by Greg Gillson.

 

Today I joined an Oregon Field Ornithologists' public field trip to Mount Tabor, in the middle of Portland, Oregon. Shawneen Finnegan and Dave Irons led the trip, and it was joined by almost 20 others.

This was my first visit to Mount Tabor, thus I was glad to have experienced local guides showing us the best birding areas.

The purpose of the field trip was to view Neotropical migrants. Migration is best with unsettled weather. Today was such a day, with 95% cloud cover and occasional sprinkles. Birds were actively moving through the tree tops, backlit by the overcast skies. Thus, while it was good bird migration weather, it was not good bird photography weather.

We didn't have a "fall out"--a spectacular migration event with thousands of birds of scores of species arriving overnight. Still, we did have good numbers of birds.

I saw several species for the first time this year, including several flycatchers: Hammond's, Dusky, and Olive-sided. The Dusky is a rather rare migrant west of the Cascades. But some migrate through the west side lowlands and then move upslope as spring advances up the mountains. We also saw a couple Pacific-slope Flycatchers.

 

Olive-sided Flycatcher, Mount Tabor, Portland, Oregon, 7 May 2011 by Greg Gillson.

 

Other birds included a rare west side (of the Cascades) Calliope Hummingbird, which I did not identify. I heard, but never saw, a Western Tanager. There were various sparrows on the slopes, identified as migrants as they weren't in habitats or areas that they would be found in during winter or breeding season. A couple of Warbling Vireos were evident in the budding big leaf maples. Numerous Hermit Thrushes were present, as was an early Swainson's Thrush.

Most conspicuous were the warblers: I saw perhaps a dozen Nashville Warblers, 30 Orange-crowned Warblers, a couple MacGillivray's Warblers, numerous Black-throated Gray, Townsend's, and Yellow-rumped Warblers, several Wilson's Warblers, and a single Hermit Warbler. These birds sing and call during migration, making warbler watching an enjoyable annual spring event.

Bird list on eBird (52 species).

 

Townsend's Warbler, Mount Tabor, Portland, Oregon, 7 May 2011 by Greg Gillson.

 

What makes Mount Tabor so good for Neotropical migrants? When is the best time to visit? That's a topic for tomorrow.

How to use eBird... To track migration

Orange-crowned Warbler, Newport, Oregon on 30 April 2010 by Greg Gillson.

 

One of the "games" that birders play is to be the first one locally to see a certain migrant. Birding listservs in spring are often titled: "FOS: ..." for First Of Season.

It is a joy to once again meet up with your bird "friend" in April or May that you may not have seen since last September. Migration is an amazing natural wonder.

However, some individual birds of many of our migrant species, may winter locally. Or, maybe there is one adventurous bird migrating early. Averaging the first arrival date over several years gives a good idea of when the first individuals of a certain species might be expected. But eBird allows us to examine migration in so much more depth.



As we discussed previously (What is eBird?), eBird is a free web-based software tool that allows you to record your bird sightings. With it you can track your personal birding lists. However, its power comes from combining your list with thousands of other birders' lists.

What follows is a detailed explanation of how to use eBird to track migration near you. I want you to be able to do this yourself....

So, the first thing I do is select a location of interest. Since I live in the Willamette Valley bio-region of western Oregon, that's where I start.

eBird.org: View and Explore Data is the tab to choose. I select the abundance Bar Charts. Then I choose my location. Oregon is the state, but now I choose Counties in Oregon and hit Continue.

eBird allows you to combine up to 14 counties at once. That is usually enough to define a smaller region among Oregon's 36 counties. I will choose the 9 counties of the Willamette Valley. In this case I am leaving off the southernmost, Lane County, as it includes part of the coast. Many birds arrive on the coast first, before the inland valleys. Not a perfect solution, but it will do.

Now eBird builds a complete checklist of all sightings ever reported in the area I specified. eBird then creates an abundance bar chart for each "week" of the year (each month is divided into 4 weeks, so some weeks have 7, 8, or 9 days).

Now I scroll down and select Orange-crowned Warbler (right-clicking on my Windows PC mouse and opening in a new tab, so I don't "lose" the entire bar chart and have to hit the "back" button and reload it all).

When the Orange-crowned Warbler page opens, it again shows the bar chart for this species. You can choose any time-frame, in one-month intervals. Below this is a map with all sightings mapped with "push pins." Click on each pin to see the location, date, number of individuals counted, and the name of the observer.

At this time, however, choose the Frequency tab. This will tell you how many (%) of all checklists in your defined area that week reported the species. This tells you how widespread the species was in your area.

Below is the frequency of Orange-crowned Warbler sightings in the Willamette Valley for the years 2007-2010 (right-click and open in new window for a larger view).



By examining the screen shot above, you can see that there are some individual Orange-crowned Warblers found in winter in the Willamette Valley. You can't really be sure if the one bird you see is the "first" detected migrant or not. However, beginning with the 4th week of March (week starting 3/22), Orange-crowned Warbler sightings jump! By the first week of May they are the most widespread, being found on 30% of all checklists reported anywhere in the counties containing the Willamette Valley.

Orange-crowned Warblers then move to the hills to breed, so they aren't quite as widespread during the summer. But in September, they start migrating south and are found in more areas, peaking (being most widespread) the 3rd week of September (week beginning 9/15). By the middle of October, Orange-crowned Warblers are mostly gone.

But now select Totals and see, not how widespread, but how numerous they are throughout the year (screen shot below, right-click and open in new window for a larger view).



Looking at this data, we see that Orange-crowned Warblers are most numerous the 4th week of April (week starting 4/22). And though the Frequency charts showed they were fairly widespread in late September, this Totals chart shows they are not numerically very common then.

How does this compare to what is written in Handbook of Oregon Birds, 2009 by Herlyn and Contreras? Well, they say: "Spring migration begins in mid-Mar along the s. Ore. coast and peaks in Apr.... Fall migrants peak in early to mid-Sep, and most are gone by mid-Oct."

Also listed are compilations of average first-arrival dates: March 21 for Benton County, and March 19 for Portland area.

So, eBird data refines the area and quantifies the general Oregon status given in this great little book.

Some of the other tabs, showing the data in other ways, may prove interesting to you. They will be more accurate as the database grows. Since eBird usage seems to be growing about 25% per year in Oregon, the information gleaned is getting more and more accurate--and interesting.

There it is, then--Orange-crowned Warbler migration in the Willamette Valley charted and graphed. We didn't look at the other tabs. I leave that as an exercise for you.

I am sure you can think of a migrant bird in your area that you would like to graph out this same way.

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