334 U.S. NATIONAL MUSEUM BULLETIN 237 pabt i 



viduals that spend the summer in the mountains of northern New 

 England move down into the lowlands for the winter, while those 

 that breed farther north at lower elevations either remain on or near 

 their breeding grounds throughout the year or move southward when 

 their food supply becomes scarce and they are forced to look for it 

 elsewhere. These movements are irregular and erratic, sometimes 

 insignificant in numbers, but at other times so impressive m volume as 

 to be called invasions. J. Murray Speirs (1939) has pubUshed 

 some data showing that, in the vicinity of Toronto, periods of greatest 

 abundance have occurred at intervals of 5 or 6 years, usually 6. 

 The records for Massachusetts show intervals of only 2 years in one 

 case, 5 years in two, and 6 years in one case, with some longer inter- 

 vals' between invasions. Ludlow Griscom (1923), referring to the 

 New York City region, says: "There have been ten marked flights 

 in the past ninety-six years, the last in the winter of 1903-04. The 

 last eighteen years is the longest interval between flights of which I 

 have any record." Some of the greatest invasions into Massachusetts 

 occurred in the winters of 1869-70, 1874-75, 1892-93, and 1903-04. 

 William Brewster (1895) has published a full account of the remarkable 

 flight that occurred during the wmter of 1892-93, to which the 

 reader is referred. 



That these great southward flights are not caused by severe winters 

 is shown by theu- absence during some of our hardest winters and 

 their presence in large numbers during some of our mildest and most 

 open winters. The movements seem to be governed entirely by the 

 food supply. Referring to the causes of these flights, Forbush (1929) 

 suggests: 



When there is a heavy crop of beechnuts in northern Maine and the southern 

 Canadian forests, the Pine Grosbeaks sometimes swarm in those regions and I 

 few come to Massachusetts, but a lack of wild fruit, cones and seeds in northern i 

 forests might compel these birds to seek food to the southward. 



* * * A dry spring and summer in the north, resulting in a scarcity of wild 1 

 fruit and seeds, may be the chief cause of the great southward flights, especially 

 if the dearth of food comes the next season after a year of plenty with its con- 

 sequent increase in the numbers of the birds. A fire sweeping through a great 

 forested region or a great eruption of spruce-destroying insects, such as sometimes 

 occurs, might have a similar effect. 



The favorite haunts of the grosbeaks during their winter visits 

 with us are the more open coniferous forests or the hillsides covered 

 with an open gi-owth of red cedars, which furnish shelter as well 

 as food; we can ahnost always find them in such places when they 

 are with us. But they also resort to deciduous trees and shrubs 

 about our homes, to orchards and to shade trees along the streets 

 of towns and cities, feeding on such fruits and seeds as are available 



