TABLE 6.--Computed Hourly Densities at Tampico, Tamps., in Spring of 1948
========================================================================= | Average hour of observation DATE |-----+------+-------+-------+------+------+------+------+---- | 8:30| 9:30 | 10:30 | 11:30 |12:30 | 1:30 | 2:30 | 3:30 |4:30 -----------|-----+------+-------+-------+------+------+------+------+---- 22-23 March| 600| 700 | 1,000 | 800 | 100 | 100 | 0 | 100 | .. 23-24 March| 0| 400 | 1,200 | 3,100 | 800 | .. | .. | .. | .. 24-25 March| 300| 700 | 800 | 1,600 |1,100 | .. | .. | .. | .. 21-22 April|1,100|7,000 |14,900 |12,900 |8,100 |3,800 |3,500 | 200 | .. 22-23 April| 700|2,900 | 7,500 | .. | .. | .. | .. | .. | .. 23-24 April| 600|4,700 |19,100 |21,200 |5,500 |5,900 |4,000 |2,000 |200 -------------------------------------------------------------------------
Among the present flight density data bearing on the above issues, are the six sets of observations from the vicinity of Tampico, Tamaulipas, already referred to. These were secured in the spring of 1948 by a telescope set up on the Gulf beach just north of the Miramar pavilion and only a hundred feet from the surf (see Figure 25, _ante_). The beach here is approximately 400 feet wide and is backed by scrub-covered dunes, which rapidly give way toward the west to a rather dense growth of low shrubs and trees. One might have expected that station densities at Tampico in March would be rather high. Actually, though they are the second highest recorded for the month, they are not impressive and afford a striking contrast with the record flights there in April (Table 6). Unfortunately, only a few stations were operating in March and thus adequate comparisons are impossible; but the indications are that, in March, migration activity on the western edges of the Gulf is slight. It fails even to approach the volume that may be observed elsewhere at the same time, as for example, in eastern Kansas where, however, the migration is not necessarily correlated with the migration in the lower Gulf area. Strangely enough, on the night of March 22-23, at Tampico, approximately 85 per cent of the birds were flying from north of an east-west line to south of it, opposite to the normal trend of spring migration. This phenomenon, inexplicable in the present instance, will be discussed below. On the other two nights in March, the directional trend at Tampico was northward with few or no aberrant components. Observations made approximately thirty-five miles inland from the Gulf, at Ebano, San Luis Potosí, on the night of March 25-26, show lower station densities than the poorest night at Tampico, but since they cover only a three-hour watch, they reveal little or nothing concerning the breadth of the so-called coastal flyway.