776 POPULAR SCIENCE MONTHLY. 



carnival lie lias only to loiter in the nearest grove to hear the won- 

 derful performance of the catbird. The catbird is the real harbinger 

 of summer. He is familiar throughout the countryside, liked or 

 disliked according to the dispositions of folks, but when he appears 

 amid the May-day throng every one knows that summer has come. 

 As a countryman once said to me : " You can't place any dependence 

 on the robin — it may snow the very day he comes ; but a catbird never 

 makes a mistake — it's summer with him for sure." 



The passing on of the great warbler waves to the north and the 

 ending of the migration likewise mean the passing of the spring. It 

 is summer any time after the 15th of May, or, to be more accurate, 

 after the last of the migratory warblers, thrushes, and tanagers have 

 passed beyond our woods. To a New-Englander summer will come 

 a little later, nearer the true almanac date of June 1st. To a dweller 

 in Virginia the last of April is the passing of spring and the advent 

 of summer. 



Some ten or more years ago several enthusiastic ornithologists liv- 

 ing in the neighborhood of Philadelphia began keeping records of the 

 times of arrival of the different species of birds, and at the same time 

 noted the conditions of temperature in relation to the abundance of 

 individuals. After several years of these observations they were able 

 to see clearly that these bird waves were directly related to the waves 

 of rising temperature marking the advent of warm spells of weather. 

 One of the most significant facts deduced from these observations was 

 the remarkable regularity in the first appearance of certain species. 

 For example, the Baltimore oriole in eight years of observation never 

 arrived before the 1st of May, and only twice later than the 4th — viz., 

 once on the fifth and once on the 7th. The list on the opposite page 

 shows the date of first arrivals extending over a period of eight years, 

 from 1885 to 1892.* 



Another fact of great interest which bears on the south-to-north 

 movement of migrating birds, and which these observations very 

 clearly brought out, was the earlier appearance of individuals of vari- 

 ous species at points nearer the river, the first arrival of the same 

 species at points back from the river being, in many instances, several 

 days later. The first report of the arrival of a given species usually 

 came from a low, marshy tract of land immediately bordering the 

 western shore of the Delaware. The second report came from a 

 locality several miles back of the eastern shore of the river, but situ- 

 ated in the low plain of the river valley and within tide-water limits. 

 The third report came from a place some miles back from the river 

 on the uplands, but near the head of a stream emptying into the 



* The Birds of Eastern Pennsylvania and New Jersey. Prepared under the direction of 

 the Delaware Valley Ornithological Club. By Witmer Stone. Philadelphia, 1894. 



