Confused Behavior of Gulls in Relation to Weather Conditions
Confused Behavior of Gulls in Relation to Weather Conditions.-Dean Amadon (Condor, 68:397-398, 1966) reported an interesting observation of gulls (probably Law californicus) milling about at night in a snowstorm, near Reno, Nevada, 22 April 1964. He was unable to suggest a reason why the birds continued to mill about for two and a half hours, or why they started migrating “on a miserable night following an even more inclement day.”
A study of the weather maps for the period in question provides a basis for explaining the reported situation which, in fact, may be considered an example of the way weather patterns disrupt the normal pattern of migration. The “Daily Weather Maps” series of the U.S. Weather Bureau for 0100 EST 22 and 23 April 1964 show that an intense cold front moved across the western states from the northwest, passing Reno in mid-afternoon on 22 April, with an average speed of over 500 miles in 24 hours. By 2200 PST a surface low-pressure area had developed, centered near Ely, Nevada. The combination of the cold front and the developing low-pressure center led to strong northeasterly winds over northern Nevada. To the west of Reno, the topography of the Truckee River canyon forms a “funnel,” which tends to channel the winds along the river.
The probable movements of migrating California Gulls in the weather situation described can be reconstructed as follows. Birds traveling from their coastal wintering areas to the breeding grounds on inland lakes north and east of Reno were already past Reno (Amadon noted that there were no gulls on Lake Tahoe that morning), traveling in the fine weather that prevailed until the morning of 22 April. The rapidly moving cold front must have caught a number of flocks over the plains, and the accompanying snow squalls and wind shift would be expected to disorient some of the flocks of gulls which had not arrived at suitable resting places. If the disoriented birds then continued flying in a random pattern, the resultant travel would be downwind. Those birds which were upwind of Reno when they became disoriented would then be carried with the wind to the vicinity of Reno. The known attraction of bright lights for confused migrants would account for the concentration noted by Amadon. I suspect that similar concentrations may have occurred at other brightly lighted spots in Reno and its environs.
The reconstruction given above accounts for the presence of migrating birds at night in bad weather, and partially exp!ains why they were observed milling about in the same area. It does not adequately explain why they remained there for a period of two and a half hours. I can offer two speculations: first, that there were a number of different flocks which, after a short period of circling, moved on in search of a resting place; second, that a single flock, unable to find either orientation clues or a safe landing spot, circled the lights, which were the only fixed point available, until the weather improved as the cold front moved on.-WILLIAM J. FRANCIS, Illinois State Natural History Survey, Urbana, Illinois 61801, 30 November 1966.