Bird Migration

Bill Young

Many birders want to know the best time of day and best weather conditions to visit Monticello Park during the spring bird migration. There are no simple answers to these questions. In general, bird migration is a process about which surprisingly little is known. I have found that people who try to use wind direction and radar readings to predict if Monticello will be active on a particular day do not do better than if they had flipped a coin.

Bird migration is immensely complicated and involves a great many variables. I have been at the park on overcast days and seen big fallouts, and I have been there on sunny days and seen few birds. I have been there first thing in the morning and seen a lot of birds, and on other mornings, I have seen hardly any. I have been there late in the afternoon when many birds came to bathe, and on other days, I have seen few birds late in the day. The park can be full of birds during one hour and quiet the next. Mid-afternoon can be really active or very quiet. I have had great days when the winds had come from the north the night before and slow days when the winds had come from the south, which is the opposite of what some people expect.

In general, hot conditions are better than cool ones, and calm conditions are better than windy ones. If a day is sunny and hot, the birds are more likely to come down to drink and bathe, including after noon. The least productive time is often between 1 and 3, but that period can sometimes be very active.

Wind speed and direction can be important. Songbirds generally migrate at night when temperatures are cooler and to avoid predators. They often will land at daybreak to feed after flying all night, which is why birders are advised to go out early in the morning during the spring. One reason Monticello is such a good place for songbirds is that it is on a ridge. The migrating songbirds see the trees in the park and surrounding neighborhood and land there to feed. Songbirds will generally feed and drink actively for about four hours after they land and then either rest or feed for the rest of the day before deciding whether to continue their journey. If wind conditions are not favorable when they are ready to take off or if they have not had enough to eat, they might stay two or more days.

You cannot simply look at the direction of the previous night's winds and determine whether there will be a lot of bird activity at the park the next day. During the spring, it is too simplistic to say that winds from the south are good and winds from the north are bad. The forecast for wind conditions is an average of what will be felt at ground level, but songbirds do not fly at ground level. Most migrating songbirds fly at altitudes from 500 to 2,000 feet, but some fly as high as a mile off the ground. Their typical speed is between 10 and 30 miles per hour. The winds can be different up where they fly. Winds from the north might discourage a lot of songbirds from expending the extra energy needed to fly into the wind, and the birds could decide to stop at Monticello or someplace else. If winds are from the south, some birds might get blown into or out of Monticello. Other birds might bypass our area and keep flying, depending on how much fat they have accumulated. Winds from the east or west can either blow birds into the park or blow them onto a migration route away from the park.

Very few songbirds die on their wintering grounds. During some years, less food during the winter might mean that they have put on less fat and will need to stop more frequently to feed during migration. The more frequently they need to stop along the way, the more likely they might stop at Monticello. What is bad for the birds can be good for birders, and vice versa. During the spring and fall bird migrations, the Cornell Lab of Ornithology website posts a live migration map which shows the intensities of actual bird migration as detected by the US weather surveillance radar network. The map shows bird movements through the different parts of the United States. However, the radar used for the map cannot detect what species of birds are migrating or whether they will land at a small park such as Monticello. The radar is useful only for detecting broad trends.

Birds take different routes to reach Monticello Park during the spring. Some fly from their southern wintering grounds over land for most of the trip. Others fly across the Gulf of Mexico, which is more dangerous, but cuts a lot of distance from the trip. You can learn about the trans-Gulf migrants from the video Gulf Crossing: Story of Spring, written and produced by Jackson Childs.

Scott Weidensaul wrote an excellent piece in the Spring, 2017, issue of Living Bird about how technology is helping to unravel some of the mysteries of bird migration. And the Smithsonian Migratory Bird Center has prepared a useful FAQ page with information about migratory birds.

Some people read reports about birds seen at Monticello but see few of these birds when they visit the park. Many of the reported birds are heard rather than seen. The greatest number of warblers in the spring usually arrive after the trees are leafed out, and people do a lot of birding by ear, which is why learning the songs and calls is so important. Sometimes, seeing birds at Monticello requires luck as well as skill. Even when birds are seen in the park, you might not be in the right place when they come down from the treetops. A warbler might show itself for 30 seconds, and if you are not in a place where you can see it during those 30 seconds, you will miss it, which can be frustrating. That bird might not show up again for hours, if at all.

The daily bird lists in the Birds section of this website show the likelihood of encountering a particular migrant species on a particular date in April and May. The lists are based on past experience, but birds do not always obey past experience. Some species whom you might expect to be in the park on a particular date might not be there, while other species who are unexpected might show up.

You are more likely to enjoy a spring visit to Monticello Park if you go without expecting to see particular migrant species. If you see a lot of species, you will be pleasantly surprised. If you don't see many migrants, you will still be able to enjoy the nature in the park or see some of the resident birds. There always will be something worth seeing or experiencing.