INTRODUCTION. . 25 



with such meteoric swiftness. There is absolutley no proof that any of these 

 plover- pass from Labrador to Brazil at one flight, nor do we know even ap- 

 proximately the time taken for the trip as performed. Presumably they 

 do make flights of 300 to 400 miles without rest, since they are often seen 

 passing Bermuda without resting, and have prohabhj flown continuously 

 since leaving the North American coast; yet should they tire there is no reason 

 whatever why they should not rest upon the sea at any time except during 

 storm, and it is well known that in case of heavy storms thousands of them 

 do alight on the Massachusetts coast, as well as on Bermuda, w^hile the species 

 lingers regularly for weeks on some of the West Indian Islands. 



Doubtless one reason why migrating birds fly at great heights in fair 

 weather is because it is easier. So long as the breeze is in the right direction 

 they utilize it to the full, but if compelled by circumstances to face a wind 

 they find it far easier to fly near the surface where they can take advantage 

 of such eddies and counter currents as may appear, and where at all events 

 the velocity of the wind will be less than at higher levels. Another and 

 possibly the strongest reason for flying at great elevations lies in the fact 

 that the view thus obtained is of paramount importance to the migrant. 

 At a height of two miles a bird in clear weather commands a view of an area 

 nearly 200 miles in diameter, so that under favorable conditions, it might 

 cross any of our great lakes, or even reach South America by way of the 

 West Indies without ever being out of sight of land. Should the weather 

 become unfavorable, however, after a start has been made, the little travellers 

 must make the best of a bad matter and meet the emergency as best they 

 may. Were they gifted with the extraordinary powers popularly assigned 

 them they would rarely or never be caught and overwhelmed as they so often 

 are. Were they able to fly even seventy-five miles an hour, they could flit 

 to safety on the first appearance of bad weather, well knowing that a few 

 hours of clear weather would enable them to recover all the ground lost. 

 In spite of the general belief that birds are able to foretell meteorological 

 changes and forestall dangerous storms, the weather is very largely responsible 

 for the terrijjle destruction which thins their ranks and brings death to so 

 large a proportion of our bird population every year. 



In the winter of 1894-95 most unfavorable conditions in the south nearly 

 annihilated the Bluebird and so far reduced the number of Robins reared in 

 this section of the north that their normal numbers were not regained for 

 at least six years. 



It is clear that, on the average, as many birds die each year as are born, 

 else the individuals of any species would increase in numbers year by year 

 until they became intolerably abundant. As it is, some species increase for 

 a time and then their numbers fall away again. There is a constant oscilla- 

 tion in numbers with occasional decrease to such a point that recovery becomes 

 impossible, and the species becomes extinct. Ordinary minor oscillations 

 may occupy but a few years, but more often apparently one or more decades 

 may be required for the completion of such a cycle. 



We have no time to go into the causes of mortality among birds, but it is 

 evident that a very large percentage of the young and inexperienced birds 

 which start south in autumn never return to their birthplace — probably having 

 perished from the dangers of the trip. As a rule the southward journey is 

 made — or at least might be made — with compai'ative safety. There is no 

 need of great haste, food is abundant and the travellers are moving always 

 toward regions of increasing warmth and superabundant food. On the 

 northward trip on the contrary, the birds often are leaving safety and abund- 



