Photo by Corey Husic

Sunday, March 27, 2011

It really is spring!

Spring rarely comes gradually and progresses daily toward summer. Instead, it comes in fits and starts, and then falls back to winter-like conditions. We have been in one of those “back to winter periods” here in eastern Pennsylvania for the past week. On March 17 and 18 the temperatures soared well into the 60s in northern Lehigh County and southern Carbon County. Two days later, the ground was covered with snow, and the temperature has barely been above 40ºF since then.

Many people wonder what birds like American Robins do when this happens. They congregate in warmer places, where perhaps they can still find invertebrate prey where the sun is warming the soil, but mostly they rely on their emergency rations of sumac berries.

American Robin eating Sumac berries. Photo by Dave Levandusky

All of the plant and insect signs of springs went on hold with the deep freeze. The Milbert’s Tortoiseshells went back into their dormant state and the Red Maple buds stopped swelling. The frogs went back into hiding as well, but there were some signs of spring noted this week in spite of the cold. These had to do with migratory birds.

We heard the first Phoebes singing at Lehigh Gap Nature Center on March 21. These are the first flycatchers to migrate north each spring and usually first arrive in March.

On March 24, after an overnight low in the teens and a temperature reaching about 25ºF by 9:00 a.m., I was surprised to see two Tree Swallows flying around at Lehigh Gap. Each year, a few early Tree Swallows appear, and then disappear again for a time. These are often called “scouts” since they precede the main migration of Tree Swallows.

The migration of birds, more dependent on lengthening daylight hours than on temperature, continued to bring new species. Saturday morning, March 26, we saw the first Osprey of the season hovering over the Lehigh River, just outside the Osprey House, our visitor and education center. While the Tree Swallow scouts certainly had little in the way of flying insect food with a temperature of 25ºF, as long as the water in the river is not frozen, the Osprey can catch fish.

Osprey Photo by D. Levandusky

So the birds are telling us it really is spring. Now it is time for the thermometer to agree!

Dan Kunkle

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