Monday, November 16, 2009
Migrating Red-tailed Hawks... or Not?
Many hawk watches are still looking for and seeing migrating Red-tailed Hawks. One of the things I especially like about late season migration in the northeast is that the late October/November light on migrating redtails shows them at their very best. Never are the colors richer, warmer, and more beautiful on a Red-tailed Hawk than when bathed in afternoon sunlight in early November.
However, in recent years I have been conscious of another growing movement of Red-tailed Hawks, at least in the greater metropolitan Boston area. More Red-tailed Hawks are breeding in heavily developed inner suburbs – and even the core city – than ever before, not just in the wealthier, greener suburbs. Breeding redtails now occupy virtually every major intersection on the major interstate highways in the region. In at least two intersections in my corner of inner suburbia, multiple breeding pairs occupy territories based on the four separate sets of conspicuous vapor lights, on which they frequently perch; that is, two or three different breeding pairs pair consistently perch on specific vapor lights at one cloverleaf.
I’ve also found that a number of these urban redtails – at least a number of adults – do not leave their breeding areas in the winter. Those birds whose most prominent perches are on vapor lights on major cloverleaves appear to occupy the same perches all year round. Locally nesting redtails who do not use the vapor lights generally do not appear to use their most prominent breeding perches regularly during the winter. They are seen intermittently during the winter, however, periodically checking out their nest sites. This seems particularly true for the adult females.
What happens to the juvenile offspring of these urban redtails? The assumption has been that they disperse and eventually migrate. I have not seen the one apparently still surviving young of my local redtail nest for months.
However, I have seen young of other breeding pairs in the area on the same perches – primarily on the interstates – on which I’ve seen them since they fledged months ago. Will they eventually depart for warmer climes? Or will they become part of the growing urban, settled redtail population?
Other redtails move into the area for the winter, some of whom appear to be western-type redtails. (One bander in southern New England says he has seen dramatic shifts in the wintering Red-tailed Hawk population over the past decade or so, seeing the first and growing numbers of western-type redtails.)
As indicated in the State of North America’s Birds of Prey, published by the Raptor Population Index (RPI), many hawk watches in the northeast have seen a decline in annual redtail numbers over the past four decades. Is this due to there being fewer redtails, or as in the case of the Sharp-shinned Hawk, are more Red-tailed Hawks migrating shorter distances, wintering farther north, or even wintering on their breeding grounds now than in the past? The Christmas Bird Count data for the U.S. from 1960-61 to 2008-09 shows a significant, consistent increase in the number of Red-tailed Hawks seen on CBCs. Are you seeing decreasing migrant redtails over the years, or increases in the number of year-round birds?