Wiktionary
abmigration
n. (context ornithology English) A northward summer migration of birds without a corresponding southward migration the previous autumn.(reference-book editor=Philip Babcock Gove title=Webster's Third International Dictionary of the English Language Unabridged origyear=1909 year=1976 publisher=G. & C. Merriam Co. location=Springfield, MA isbn=0-87779-101-5 pages=4)