Hummingbird Migration Update: April 30, 1998
Today's Report Includes:
Latest Migration News & Data
Ruby-throated hummingbirds continue to move into more northern latitudes, with many reports today from 41-42 N. Today's report includes sightings from Massachusetts, Rhode Island, New York and New Jersey.
Help Unpave the Way for Hummingbirds
Discussion of Challenge Question # 3
Cold temperatures and few flowers greet the first hummingbirds to arrive in the spring. But somehow these early birds find enough sugar water to get by. In fact, they often depend heavily on tree sap. But how do they get it? Challenge Question #3 asked, "How do you suppose a hummingbird can get sap from a tree?"
Obviously hummingbirds can't use their tiny peaks to dig through tree branches to get at flowing sap. However, by following in the trail of another bird, sap is readily available to them.
Yellow-bellied Sapsuckers are a kind of woodpecker. They winter in the southern U.S. states, and are one of the first migrants to appear in northern states and provinces in early spring--right when sap is running strong.
Sapsuckers migrate a good two or three weeks before hummingbirds do. They often rest for a week or two here and there between their winter and summer homes, making a temporary feeding station in a stand of trees. They encircle three or more branches with their tiny holes, and lap up sap with their furry tongues. One migrating sapsucker drilled 286 tiny holes in a pine tree in 9 1/2 hours one April day, providing a bounty of food for itself--and for other birds.
While sapsuckers are feeding at and guarding one set of holes, a host of other birds may visit the other sets. At least 35 species of birds, including hummingbirds, warblers, kinglets, and phoebes, are attracted to sapsucker borings. Not only do they drink the sap; they also eat the many sap-eating insects that are also attracted to the flowing sap. (Using binoculars, look very carefully at the top branch tips of different kinds of trees. Some may have tiny insects swarming at the newly running sap.)
As long ago as 1891, a scientist named Frank Bolles noticed that hummingbirds visit sapsucker holes more than any other birds. He saw them come to these holes throughout the summer, but especially in early spring. (Sapsuckers drill holes during the spring and summer, while sap is running. As sap dwindles, they turn to flying insects, ants, fruits, and nuts for food.)
When two species associate closely with one another, benefiting at least one, the relationship is called "symbiosis". Hummingbirds get an obvious food benefit from sapsuckers, but they also may help in return.
In northern Wisconsin, naturalist Laura Erickson spent many hours one May studying some sapsucker trees. The woodpecker had drilled circles of holes in three different aspen branches for feeding. While the sapsucker fed or rested on one branch, Erickson watched other birds come to the holes in the other 2 branches. Most of the time, two or three birds gorged themselves at each feeding spot. However, whenever the hummingbird visited, he pugnaciously chased away any birds that happened to be there, except the sapsucker. While hummingbirds eat a lot of food compared to their body weight, they don't eat much compared to warblers and phoebes. Therefore, hummingbirds may be helping sapsuckers in return by defending the sapsucker's hole borings from other, larger, hungrier species.
The Next Hummingbird Migration Update Will be Posted on May 7, 1998
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