BICKNELL'S THRUSH 201 



field on May 27, but the birds moved in rapidly during the ensuing 

 few days (coincident with a thaw) and seemed to have reached their 

 peak of numbers by May 31. 



Courtship. — The belated arrival of the birds on their nesting grounds 

 and the shortened season at high altitudes necessarily curtail the time 

 available for mating and courtship. Though apparently the birds 

 are unmated at the time of their arrival, nesting activities start 

 promptly, leaving little time for prenesting nuptials. Such activities, 

 moreover, take place largely in the dim light of evening, which makes 

 observations on this phase of their breeding cycle difficult. Some 

 probable sexual flights were observed on Mount Mansfield. The 

 male pursues the female in swift flight, his crest feathers erected, and 

 bill gaping. He often bursts into passionate song as the two dodge 

 swiftly through the thickets. Such flights, however, are not restricted 

 solely to the mating period, for during incubation the male frequently 

 appears at the nest and drives the female away on a chase through the 

 trees. Such a sexual flight was once observed in July; and apparently 

 the pair later reared a second brood. 



The evening is the great playtime of these thrushes. As the light 

 of day retreats, the twilight-loving birds emerge from their concealing 

 shelters and indulge in their remarkable flight-singing ceremonies until 

 darkness envelops the woods. Occasionally they may be seen alight- 

 ing upon stumps or rocks, a perfect picture of alertness, fluttering 

 their wings tremulously as they dance nervously on their perch. 

 Though these flight-singing performances are not confined strictly to 

 the courtship period, their obvious concentration during the early 

 part of the breeding season suggests that their major role is in nuptial 

 affairs. 



Young birds exhibit sex reactions at an early age. A young bird 

 kept in confinement would, when a little over a month old, suddenly 

 mount an object' — a hand, foot, pencil, or small object on the floor — 

 press its body down close upon it, flutter its wings, and open its beak. 

 This behavior continued at intervals through the fall and winter, and 

 though it may have been a mere playful impulse, to all appearances 

 it looked like a reaction toward coitus with the opposite sex. 



Nesting. — In spite of the special interest that attached to the home 

 life of Bicknell's thrush in the period following its belated discovery, 

 the revelation of actual nesting sites and pertinent life-history data 

 has been slow, the bird's habit of breeding in isolated and relatively 

 inaccessible habitats, and of building well-hidden nests in these places, 

 necessarily hindering the gathering of such information. Known 

 nesting records, published or disclosed through correspondence, have 

 been given in some detail by Wallace (1939) and need not be repeated 

 here. In 1935, the writer had an opportunity to follow the nesting 



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