386 BULLETIN 17 9, UNITED STATES NATIONAL MUSEUM 



As we see tree swallows arriving normally in "spongy April," 

 when the weather is mild and insects are in the air, they often fol- 

 low the course of a river, either low down over the water, feeding 

 as they go, flying in long curves, often sailing on set wings over 

 the greater part of a wide circle, or well up in the air in loose 

 flocks, 20 to 30 perhaps, exchanging in their progress high, delicate 

 salutations. 



In Florida, late in February, there is a conspicuous migration 

 from farther south. I have often seen large numbers passing over 

 the Kissimmee marshes, moving steadily toward the north in wide 

 array on a broad front, hundreds flying past within a few minutes. 

 At such times they make use of a monosyllablic call that I have 

 rarely heard on the breeding grounds. At a little distance it re- 

 sembles the rough note of the bank swallow. 



Courtship. — The tree swallow's courtship apparently consists in 

 a pursuit that enables the male to display his proficiency and expert- 

 ness in flying. Dr. Samuel S. Dickey (MS.) describes thus "the 

 maneuver of mating" of a pair just before the eggs were laid : "They 

 gyrated rapidly to and fro, up and down ; then mounting still higher 

 than their previous level they dallied in midair. The male drew up 

 to the female and grasped her breast feathers with his feet, and the 

 two birds tumbled downward together, not parting until they were 

 near the ground. The female then flew to the vicinity of the nest 

 and settled down on a perch, lifted her wings slightly, and expanded 

 her tail. The male glided above her and, dropping his wings, 

 alighted on her back. I have never seen these birds have sexual 

 contact in midair." 



Francis H. Allen (MS.) states that in the courtship flight the 

 wings are never raised above the horizontal. 



Observations on banded tree swallows show that a pair may breed 

 together in successive seasons. Mrs. Kenneth B. Wetherbee (1932), 

 Oscar McKinley Bryens (1932), and Lewis O. Shelley (1934a) 

 speak of this habit, but Laurence B. Fletcher (1926) reports a case 

 in which two birds, mated in 1925, returned the next year and paired 

 off with different mates. 



Shelley (1935) has shown that male birds not only may change 

 mates from year to year but may have two mates at the same time. 

 He explains irregular matings thus: "The first Tree Swallows of 

 the season arrived at the station on April 3d, when the migration 

 of the species was nearly over. About May 1st brown females com- 

 menced to appear, and they were common throughout their migra- 

 tion, which lasted to June 16th. * * * Since these unmated 

 birds arrive to such an extent after nesting by older pairs is well 

 under way, they are susceptible to mating, and they do mate with 



