Birds and Birding's Guide to:

Watching THE MIGRATIONS OF BIRDS

Rates of Travel

Herr Gatke, whose observations on Heligoland, a small island in the North Sea, extended over a period of fifty years, would give to birds a speed that is incredible. For example, the Gray Crows were believed by him to pass over the 360 miles between Heligoland and Lincolnshire at a rate of 120 miles an hour, and Curlews, Godwits, and Plovers are said by him to cross from Heligoland to the oyster beds lying to the eastward, a distance of a little more than 4 miles, in one minute, or at the astonishing rate of 240 miles an hour.

The error in these observations, as suggested by Newton ("Dictionary of Birds,”p. 566), probably lies in the impossibility of identifying the individuals that leave one of the given points with those first arriving at the other end of the line. Professor Newton ' also calls attention to the fact that few birds, even Swallows and Quail, fly as fast as an express train from whose windows they may be observed. It is a common experience, when a train is passing along at no great speed, for various birds to be flushed by it, but after flying vigorously for a few hundred yards they quickly drop behind.

But granting that the occasional speed is very considerable, the actual speed of most migrating birds appears to be surprisingly low. Observations tending to prove this were made some years ago under the direction of Professor W. W. Cooke, in the Mississippi Valley. The services of over one hundred observers were enlisted, at stations ranging from the Gulf to Manitoba.

The date at which a certain species was first noted at the most southern point was compared with the first appearance of that species at the most northern point; the distance in miles between these two stations is then divided by the number of days between the observations. Thus the Baltimore Oriole was first seen at Rodney, Mississippi, April 7, and was not observed at Oak Point, Manitoba, until May 25. The distance in a straight line between these two places is 1298 miles, and as it took 48 days, the average speed was 27 miles a day.

The records of fifty-eight species for the spring of 1883 gave an average speed of 23 miles a day for an average distance of 420 miles, while in the following year a slightly smaller number of species gave exactly the same average speed over an average distance of 861 miles. In the case of individual species the results were of much interest.

Thus the Robin, Cowbird, and Yellowhammer traveled at an average speed of about 12 miles a day, while the average for the Summer Redbird, Ruby-throated Hummingbird, and Nighthawk was 28 miles a day. It is, however, necessary to take so many things into account in arriving at these conclusions that it is easy to see the possibilities of error. For example, meteorological conditions play an important part during migrations; a rain storm or an unusually cold spell may retard progress for days.

Even if the conditions are favorable, it is hardly probable that the same individuals migrate for more than a night or two without intermission, so that while the species may be making progress the individuals are alternating a night or two of travel with often several days of rest and recuperation. Again, it was found that most species traveled considerably faster during the latter part of the journey than during the first part. Thus six species showed an increase of 77 per cent in speed for the northern half of their journey, and the same general result was obtained by calculating the average speed of twenty-five species separately for each of the different months in which migration is performed; the average for March being 19 miles, for April 23 miles, and for May 26 miles a day. The species which are late migrants also move faster than those which start earlier and take more time about it.

 

 

previous bird species next bird species