Experiments on the homing ability of Purple Martins

TitleExperiments on the homing ability of Purple Martins
Publication TypeJournal Article
Year of Publication1968
AuthorsSouthern WEdward
JournalLiving Bird
Volume7
Pagination71-84
KeywordsPROGNE
Abstract

To test the homing ability of Purple Martins (Progne subis), Douglas A. Lancaster, Larry L. Wolf, and the author used 92 birds from two colonies in northern Michigan. The data from these trials, made in 1959, 1960, and 1962, were added to the data from the author's tests on 16 birds in 1958. Individuals were released at eight compass directions and at distances up to 594 miles from the colony. Fifty-five martins were released at one site, at different times, in an attempt to determine the influence of weather; 74.5% returned. The success rates for groups released at different directions from the colony ranged from 66.7 to 100% with an average of 79.8%. The rates declined as the distances increased. Similar tendencies were shown in initial departure headings. Of 12 juveniles, released at distances up to 250 miles from the colony, only two, both released within sight of the colony returned. Of 56 adult females tested, 44, or 78.6% returned from distances between 1.75 and 415 miles. Of six subadult males tested, four, or 66.6% returned from distances up to 385 miles. Both sexes showed similar tendencies for returning. A definite correlation was noted between the stage of nesting and homing success, with more birds returning during the egg and small young stages than later in the season. The initial flight behavior upon release did not indicate the homing performance to follow. Some of the recorded behaviors may serve as a displacement function. There was no correlation between wind bearings or velocity and preferred headings. Nor was there any correlation between the homing results and magnetic disturbances in 1962. Flight speeds ranged up to 27.37 miles per hour and the average homing speeds decreased as the distance of the release sites from the colony increased. The average for 36 individuals, released 249 miles SSE of the colony, was 7.24 mph. Homing performances varied greatly between individuals and no evidence was found to support the occurrence of true navigation and the use of solar clues in a bicoordinate method. There was equally little evidence to support the use of other types of clues for orientation. Most of the circumstantial evidence tended to support the use of geographical landmarks. As a result of these experiments the author feels that the use of homing trials is not a satisfactory means of determining the method used by birds for orientation and that a new approach must be developed before we can advance our knowledge of the technique of avian orientation.