Rosy-finch banding has been carried out at Sandia Crest since 2004. The first Coastal (Hepburn's) race of the Gray-crowned Rosy-Finches (5 individuals) were captured during the winter of 2005-2006.
The influx of the Hepburn’s race at Sandia Crest peaked in the winter of 2006-07, when the Rio Grande Bird Research team newly banded 104 birds (representing over 13% of all rosy-finches banded that winter).
During the winter of 2007-2008 the percentage of Hepburn’s decreased to 29 birds (6%). This past winter, as of March 15, 2009, they represented only only 7 of the 276 captures (down to 2.5%).
Little seems to be known about the reasons for fluctuations in species mix from one winter to another. We have seen unusual patterns of abundance in the Brown-capped species as well, both at Sandia Crest and in Estes Park,Colorado. This is an area ripe for research into possible factors, whether they may be related to climate fluctuations, local weather or habitat changes on their distinct breeding grounds and migratory routes, food supply, population pressures, and so on.
Do these fluctuations in the mix and relative abundance of the various species and races correlate with the irruptive behavior of other northern finches?
The spreadsheets at this link provide day-by-day banding statistics, compiled since 2004. Their analysis may provide a starting point for further research.