Cattle Egrets in Oregon, 1984

Cattle Egrets first appeared in the U.S. (Florida) in 1941 and the first one seen in Oregon was in 1965. Since then, during some winter seasons, large groups have appeared briefly in Oregon, but then have soon disappeared. Recently there has been some conversation among Oregon birders wondering why this seems no longer to be happening, but there is no obvious answer. Are there not enough bugs here? The photo above was taken near Logsden in Lincoln Co., Oregon, in 1984. On December 8 that year there were 38 Cattle Egrets in this cow pasture.