I recently did some rapid research into Northern Cardinal vagrancy/dispersal - specifically the 1995 movement of NOCA into Quebec - and suddenly had Ross's and Ivory Gulls on my mind instead. Why? Well I came upon a rather remarkable looking storm that occured in NE North America from Nov 11-12, 1995. This one:
(worth noting, on this and other images, I've added the coloured arrows to indicate higher elevation airflow & temp)
While it provided an interesting/reasonable reason for a rash of Northern Cardinal records into southern Quebec in the Nov 11-13 timeframe, I also asked myself "What, if any, interesting birds arrived in southern Ontario?"... A quick search of the OBRC database and I had my answer: Nov 12, 1995 - Ross's Gull found at Fort Erie, ON
Nov 12, 1995 - Ivory Gull found at Lake Dore, ON
So what connection is there to a blast of hot air & Northern Cardinal vagrants, with the arrival of the coolest/coldest gulls there are? A look at the Nov 12, 1995 surface analysis provides some clarity, with wicked NW winds pushing into southern Ontario directly from James Bay (which indicates to me, that both of these birds very likely "arrived" on Nov 12, 1995):
The elongated nature of the low pressure likely yielded a suitable pathway for birds aloft towards the eastern Great Lakes, rather than a typical fall storm which "wraps up" and bends airflow from James Bay towards the Gulf of St. Lawrence... BUT... As astute readers will already have realized: 1.) Strong winds from James Bay are not terribly unusual and 2.) Neither Ivory nor Ross's Gulls "come from" James Bay...
SO - as with many *very* rare birds associated with weather events - there was likely a series of events (or just one previous weather event) that led to Ross's and/or Ivory Gulls from Labrador Sea being displaced into Hudson Bay, James Bay or even inland Quebec, and then subsequently displaced further by the Nov 12, 1995 storm into Southern Ontario. It's hard to pinpoint the exact event, but several other notable storms occured in proximity to the Labrador Sea in the preceding days. A rather powerful low pressure system on Nov 9, 1995 seems like a potential culprit (at least for the first displacement kick into Hudson Bay):
Even beyond that, it's hard to properly predict vagrancy when dealing with 1 or 2 remarkable birds... While I am rather confident that the weather played a role in bringing these vagrants to Southern Ontario, I can't say if other factors even initiated the potential for vagrancy in the first place (i.e., normally they would "ride out" a storm and not allow themselves to be pushed off course/inland)... Sea surface temperatures in the Labrador Sea were remarkably cold, plus there was the onset of a moderate-strong la nina event in the fall of 1995 - so perhaps alterations in food availability becomes an initial trigger... But either way, this was a fun exercise in researching old bird records and weather data!