SPNayor, 1979 Journal NARE, Barrow, Alaska 23June (contd) migration in relation to the timing of melt off. Imagine a threshold % snow cover: when a bird reaches that % it settles. Then in early melt years birds would continue further (remember that Barrow + other near-1/2 boreal areas are delayed in melt compared to the tundra just 30 miles away). And they might pile up at Barrow. The degree to which this caused large variations in density would differ very among species, as affected by their philopatry, especially that of 1st year birds. But all that is hare- brained speculation.