^°''i9i^"^] TYi^^n, Call-notes of Migrating Birds. 141 



comparatively few birds, — only those which were nearly overhead 

 at sunrise. As a matter of fact, some birds do not alight until 

 long after sunrise, and some others continue their northerly or 

 southerly progress after alighting in the trees, but the explanation 

 above accounts for the seeming diminution of the number of migrat- 

 ing birds when the night's flight is over. To explain the heavy 

 spring flights when no nocturnal notes are heard, it must be under- 

 stood that bird-notes are very rare on any night in spring. The 

 contrast in this respect between spring and autumn is so striking, 

 that we are led to believe that during the spring nights, we do not 

 hear notes from migrating birds because they do not utter them. 

 If the birds do call during their northward journey, practically all 

 of them fly at a great height, thus adopting a very difl^erent manner 

 of migrating from their habit in autumn. 



Although the problems presented by the two migration trips 

 must be essentially the same to the birds, it should be remembered 

 that the personnel of the migrating horde differs in one important 

 respect; — whereas, in the autumn more than half of the migrants 

 have never made the journey before, in the spring, every individual 

 has safely accomplished at least one trip. We have surmised that 

 the migration-call may be an outgrowth of the young bird's food- 

 call. Taking into account the frequency in autumn of the migra- 

 tion calls, as opposed to their comparative absence in spring, may 

 we not further surmise that it is chiefly the birds of the year which 

 we hear calling during their initial migration and that these young 

 birds, returning over the path they travelled six months before, 

 and flying with the assurance and self-confidence which experience 

 has given them, do not need migration calls for guidance or en- 

 couragement and therefore do not utter them? 



