KOCH JC & BOUMA JP (1934) Considerations on migration. LIMOSA 7 (4): 168-171.

From 1930 could herfstrek of some species the Ring Station Wassenaar accurately counted in a graph are determined. The number of employees was note} possible to capture both the rings and as accurately as quantitative observation of possible about upcoming birds to accomplish. Let n counts based on a 4 hour observation and were observed at a shorter 4-hour period is reduced, whereby the black dagzuil the observed number and the shaded column of the supposed suggests. A shaded column ending with sloping upper end points to the perception of eenhelper for our absence. Armed with the eye was a strip of about 500 M. width and covered within this range in the notes Of course mistakes. The columns give so no means the absolute numbers on, but there in successive years more whey similar mistakes will , is still a zoodoende material is obtained which is not aileen almost the whole autumn migration exercise for 5 years graphic suggests, but that the ratio vergeIijking of numbers and the various anomalies demonstrates.

[free pdf] [dutch summary]