Well, I’m crossing my fingers and hoping that we are finally done with the snow, snow, snow Apri land have moved on to the spring April . We still have a few days left, and as we know, anything can happen, and has this month! But the warmer weather should be with us for at least a few days. Time for that spring bird migration to really pop!
So how will we know when it really pops? We should start seeing new birds for one, but there are other ways beyond looking to see what is new in the neighborhood. Turns out that we can watch weather radar. Really, radar? Yup, really radar. But before I get into that, a little background information would be a good thing to help it all make sense.
Some species of songbirds fly incredible distances twice a year. Many of these, are called neotropical migrants. This means bird species that nest in Canada or the US and then fly to Mexico, Central America or even South America for the winter. There are thought to be about 200 species of birds that make these lengthy migrations. Many of these birds are warbler sized. So how big is a warbler? In general, much smaller than your clenched fist and can weigh as little as the equivalent of a dime and a quarter in your pocket! So here’s an example- we banded a Blackpoll Warbler on the 22nd of September of 2012, at Sugarloaf. It weighed about 11 grams, or about 2 quarters in your pocket. This bird travels from our area or even further north to Northern South America for the winter, a migration that can range from 2,500 to 5,000 miles for a single bird. That’s a long ways for a bird to travel- how do they manage it?
It turns out that there is definitely some strategy to all of this. Most songbirds migrate at night. This is done for a variety of reasons. For many, it could be a way to avoid predators, who generally fly during the day. It’s cooler at night and since flying generates heat, it is somewhat easier to regulate the amount of energy needed. Nearly all songbirds are daytime feeders, so think about it, if you migrated all day- when would you eat? If they migrate at night, they can rest and eat during the next day(s) to regain their strength for the next round of flight. There is not a lot of space for energy storage in the form of fat, and the energy they consume is quickly burned in the process of flight.
Songbirds like the Blackpoll Warbler can fly at speeds generally somewhere in the range of 10-30 miles per hour. 30 mph seems slow to those of us used to driving automobiles but imagine doing that on your own steam! Blackpolls are also unique in the migratory warbler world. They typically migrate to the southeast rather than directly to the south, which means that their migration to Northern South America always includes a long non-stop flight over the Atlantic Ocean. On average it takes them about 3 days to make this roughly 2000 mile journey, meaning that they have to travel about 660 miles per day. To put that in human terms, imagine you were running 4 minute miles- you would need to maintain this speed for 80 hours straight!
Most songbirds are not quite that extreme but it can take from a few weeks to as long as 4 months to complete their migration. There is a difference in length of time spent in migration from fall to spring. Fall migrations seem to be a little more leisurely, while spring migrations tend to cover distances more rapidly, especially as they get closer to their nesting region. Small birds like Blackpoll Warblers are definitely impacted by the wind. Winds are usually stronger at higher altitudes than at the surface of the earth and most songbirds fly in the range of 500 to 6000 feet about the earth. When they are able to take advantage of the wind at their back they tend to fly at higher altitudes. Flying into the wind will generally have them flying at lower altitudes.
So where does the weather radar fit in all of this? Well it turns out that masses of birds tend to take advantage of the same optimal conditions and move together, so much so that they are actually visible on weather radar. Peak times seem to be from roughly an hour after sundown to the maximum just before midnight and a gradual decline in the hours after than until dawn. If you know how to look you can track the radar yourself. But an easier way is to check with a website (woodcreeper.com) that keeps track of this for us. Our snowy April has definitely kept the bird traffic into Minnesota to a slower pace. In fact the storms of this week actually showed some birds in Iowa and Wisconsin doing reverse migration to the south earlier in the week. The best day of the early part of the week was in the early hours of April 21. See composite image below that summarizes the nights traffic. The birds are the round blobs showing over areas with radar, the darker the blue, the more birds moving. Weather systems tend to be darker than the birds- in this case, greener and more drawn out rather than round- see the system in south Florida for comparison.
During the other days of this week there has been virtually no motion to the north in Minnesota. The latest image from the early hours of April 26 is below. Yahoo, there was movement last night, so we should be beginning to see some new birds today! Be on the lookout!
These updates are made possible by a generous donation from David and Rosemary Good.