10 Trofis. Acad. Sci. of St. Louis. 



In years of drouglit during August and September, and such 

 yeai-s are by no means rare, migrants proceed southward on 

 iheir journey without much delay, because insect food of the 

 kind they like is scarce, and all birds need water for drinking and 

 bathing.* The drying uj) of water courses and ponds has much 

 to tlo with the early disappearance of birds from their breeding 

 ground. The con(iition of our lakes and rivers governs the 

 occurrence and abundance of water-birds in autumn. Should 

 our rivers be so full as to cover all sandbanks and mud flats, 

 waders will not remain with us; on the other hand, ducks will 

 be rare when our ponds and sloughs are very low or dry, or when 

 the water is too deep for dabbling. The presence or absence of 

 particular species at certain seasons is therefore the direct result 

 of the great variation in the seasonal distribution of precipi- 

 tation. 



In winter, too, it is the abundance or scarcity of snow on the 

 ground that regulates the presence of birds more than the tem- 

 perature does. Fortunately in most winters we cannot com- 

 plain of too much snow, though the average snowfall for the 

 state is said to be eight inches in the southeast, and thirty inches 

 in the northwest. First snows usually do not fall before the 

 middle of November; but here, too, the exceptions are almost as 

 frequent as the rule. Snow once covered the ground at St. 

 Louis as early as November 5 and did not entirely disappear 

 from the north sides of houses until the middle of April (1881). 

 In another year (1889) there was no precipitation of any kind 

 during the entire fall and winter until the first of January, 

 1890, when exceedingly heavy rain and wind storms followed. 

 Snows falling before Christmas are usually light and drifted by 

 the accompanying cold and high winds. Such snows do not 

 affect bird life seriously, because they leave much ground un- 

 coveretl and accessible to the ensuing sunshine. The worst kind 

 of snow, that which is introduced or followed by freezing rain 

 and sleet, falls mostly between the fifth of January and tenth of 

 February', generally in advance of our severest polar waves 

 whose low tenvperature preserves the icy crust almost intact 

 for days and weeks. They are naturally very destructive to 

 bird life, the more so the further southward they extend and the 

 longer they last. It was one of these periods that came near 

 exterminating our eastern bluebirds in February 1895. 



The deepest snows fall in the latter part of winter, from the 

 last of February to the first of April, but remain on the ground 



