Varied Extent of Damage 
Wot only ig the zone of severe blackbird damage narrow, but from 
year to year there may be great fluctuations in its extent and severity. 
Rains during the sprouting season tend to increase the damage by malzing the 
ground soft and easily probed by birds. A harvest delayed by inclement 
weather exposes the shocked crop to attacks not only of the resident black— 
birds but also of migrants that arrive from the north in October and 
November. Such climatic conditions as the prolonged drought that occurred 
during the latter part of 1924 and the early part of 1925 also affect the 
activities of the birds, causing then to avoid vast areas of burned-over 
marsh that normally support a large breeding vopulation. 
In 1924, tests made by a rice-growing company in Louisiana indicated 
a crop loss as great as 22 percent on certain fields close to the virgin marsh. 
In the following year similar tests, many of which were carried out in the 
same fields, disclosed no appreciable damage. For the entire rice~growing 
area of Louisiana, including the zone of severe damage as well as the great 
acreage in which injury is infrequent, the average annual loss to the rice crop 
caused by blackbirds probably does not exceed 1 percent of the yield. Although 
such an estimate might appear to minimize the importance of the problem, it 
must not be overlooked that the great bulk of the damage occurs in a limited 
area and that in this area rice growers suffer severe losses. It was to remedy 
conditions in such sections that experiments in blackbird control were con- 
ducted. 
Wandering Flocks 
lackbirds are nomads. Daily they make trips to and from their feeding 
grounds in the rice fields and their roosts in the marshes. Sometimes the 
flocks number tens of thousands. With widely available food the birds may be 
in a certain locality one day and miles away the next. At times, however, they 
persist in levying toll on particular fields and may be found day after day in 
the same section. Suddenly they may leave and, like a tornado, strike at 
some distant point. Unlike field mice, ground squirrels, or other rodent 
pests that are to be found not far from their runways or burrows, the presence 
of blackbird flocks cannot be predicted with certainty. This is especially 
true during the period of ripening grain and at harvest, when there is food 
to be had everywnere. Even during the planting season, when the natural food 
supply is at its lowest ebb and the newly seeded rice fields are the principal 
attraction to the birds, their uncertain wanderings prevent the carrying out 
of consistently successful control measures. 
Legal Status of Blackbirds 
On June 20, 1936, the President approved an act, 49 Stat. 1555, amend— 
ing the Migratory Bird Treaty Act of July 3, 1918, to afford protection to 
additional migratory birds by extending its provisions to the treaty between 
the United States and the United Mexican States, which was signed on February 
7, 1936, and ratified on March 15, 1937. Among the birds thus given protection 
are those of the family Icteridae, including orioles, meadowlarks, and black— 
birds. , 
wees 
