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Cold spring - how did our 2011 migration fare?

Cold weather means birds have to stay at valley bottom before heading upslope



Environment Canada's Chief Meteorologist, David Jones, has declared the spring of 2011 the second coldest (and wettest) on record, as if we didn't already suspect so. Only the 1955-year was worse, and as I recall, it was the time of my first ski touring trip into Garibaldi Park with the Varsity Outdoor Club (UBC) in early May. New powder snow at Garibaldi Lake fell several days before we left in mid-month to catch the train and ferry back to Vancouver in blazing sunshine! This year there was no such break, and the provincial snow data authorities have noted the snow pack to be increasing throughout the spring over the entire southern half of the province. Surely the weather or prolonged snow pack had some impacts on the migratory timing of our avian friends.

Well, the first impact was on our largest bird; in 2010, Mike Gill parked his sleek single-engine Otter at the Green Lake base on March 29. This year his bird had to wait until April 29 before the ice melted off so he could, once again, start his flying season. For the organic birds, there were some similarities.

Although many birds arrived on time, or even ahead of their usual schedule, several had to stay at valley floor level for much longer than normal before proceeding upslope to their usual summer haunts.  Juncos, Golden-crowned and Fox Sparrows, Varied and Hermit Thrushes, and Yellow-rumped Warblers were in that bind. Surprisingly, however, most of the waterfowl tolerated the ice-covered lakes and made do with the small stretches of open water that were around shore edges or on river channels.

Much to our amazement, 157 species were tallied during the spring period with 108 of them being migrants. This is comparable to other years. Waterfowl arrivals were at usual numbers despite the drawbacks, arriving in several waves, the last being after a major storm on May 17th, to bring their total species numbers to 32.  For songbirds, the numbers were mixed - robust for robins, juncos and Yellow-rumped Warblers, average for a few and decidedly sparse for many others. For raptors, game birds, doves and the air-borne sky-divers, numbers are about normal, but shorebirds were decidedly few in number, especially the sandpipers, although Bonaparte's Gulls had two days of big numbers.

Last year, we went through 14 years of data (1997-2010) to calculate an average arrival date for about 130 of our migrant birds. So, how did the timing of the 2011 migration arrivals stack up against the long-term averages? A species was deemed to have arrived on time if it appeared within three days of the calculated average day; that is, our observations have about this much leeway. During spring season, our favoured birding routes (Green Lake Golf Course, Lorimer Road to Rainbow Park) are each traversed two times each week, and on two other days the observations can be elsewhere on the mountains, Shadow Lake, Alpha Lake, Calcheak, etc.  So, here are the surprising results: