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From the February 2008 Conservationist

group of evening grosbeaks at feeding station

Disappearing Act

Evening Grosbeaks vanish from feeders

By David Bonter

Watching your bird feeders this winter is likely a very different experience than just a few decades ago. The northern cardinal, red-bellied woodpecker, tufted titmouse and Carolina wren are relatively new additions to many New York backyards and continue to expand their ranges to the north. Not all species, however, are doing as well. The mysterious decline of the evening grosbeak-once one of the most common birds at winter feeders- has many long-time birdwatchers missing these raucous finches, and many scientists wondering where the birds have gone.

In 2005, a few boxes of old bird-banding data were donated to the Cornell Lab of Ornithology by a relative of a retired bander, Stuart Wilson, Jr. A bird bander myself, I immediately appreciated the meticulous records maintained by Wilson and began to leaf through the musty journals. What amazed me more than anything was the section detailing Wilson's encounters with evening grosbeaks. Between November 1957 and January 1965, Wilson banded 4,357 grosbeaks around his home in Deposit (located between Catskills and Binghamton). Grosbeaks represented 32% of the 13,695 birds he banded during this period-more than twice as many as the next most common species, the dark-eyed junco. While juncos remain one of the species most commonly seen at feeders today, evening grosbeak sightings are so rare in many parts of the state that they now warrant posts on rare bird email lists. Contemporary birders travel long distances in winter for glimpses of these gorgeous gluttons as they voraciously devour sunflower seeds at the few locations still hosting grosbeaks.

Wilson's journals are remarkable for many reasons; foremost, the reality that his grosbeak records simply could not be matched today. Wilson once banded 59 grosbeaks in a single day, January 17, 1959, and frequently banded more than 40 per day. Today it is very unusual to see 59 grosbeaks in New York in a single day. According to data submitted by more than 650 New York-based participants in Cornell's Project FeederWatch, only 16 of 8,267 checklists submitted during the winter of 2005-06 reported more than 50 grosbeaks.

Many of the grosbeaks banded by Wilson stayed near his home for extended periods, as indicated by the series of dates etched in green ink next to individual band numbers in the journals. One adult male grosbeak was captured 11 times during the winter of 1957-58 and returned for several more winters, until it was last captured in April 1962 when the bird was at least six years old.

Dozens of birds banded by Wilson traveled great distances, with multiple reports of birds recaptured in Manitoba, Quebec, New Brunswick, and several of the United States. For instance, Wilson banded an adult female grosbeak on April 11, 1961 that was recaptured near Newcastle, New Brunswick, only two months later. Another interesting recovery was of an adult male that Wilson banded in 1957 which was recovered after striking a window at the home of Margaret Tapp of Port Arthur, Ontario, four years later. In a letter, Mrs. Tapp reported to Wilson that the bird was stunned by the window collision, but she brought the bird into the house to revive him. Her letter concluded, "Apparently this bird has done some traveling and is in excellent health."

In addition to the birds he banded, Wilson recaptured at least 121 grosbeaks at his home that were banded in other parts of North America. These "recoveries" recorded movements of birds originally banded in 13 different states and provinces, ranging from Virginia in the south, to Wisconsin in the west, to Ontario in the North, and Maine in the east. In the 1950s, recoveries of banded birds were the only means that researchers had of tracking birds and learning about migratory movements. Although satellite transmitters can now be attached to the backs of larger birds like eagles and albatrosses, recoveries of banded birds remain the primary means of understanding the movements of small birds today.

Scientists monitor populations of birds throughout North America thanks to networks of volunteers who follow simple protocols for counting birds and then send their data to researchers. Project FeederWatch (see the December 2002 Conservationist) is an example of a citizen science program that has provided much information about grosbeak populations for the past 19 years. The Cornell Lab of Ornithology and Bird Studies Canada operate FeederWatch, and more citizen scientists participate in FeederWatch in New York than in any other state or province. The enormous wealth of information from participants in New York allows researchers to reliably track bird populations in the state-the more observers, the more reliable the data will become.

While populations of many common feeder birds have done well in recent decades, the evening grosbeak stands out in contrast. Only 3% of the 658 FeederWatchers in New York reported sightings of grosbeaks at their feeders in the winter of 2005-06. In comparison, 37% of sites reported the species as recently as the winter of 1990-91. Beyond New York, FeederWatchers from across North America have also documented a decline in the prevalence of evening grosbeaks. Once the fifth most common species reported by FeederWatchers in the Rockies and Pacific Northwest (seen at 62% of FeederWatch locations in 1991), grosbeaks have nearly dropped off the charts, falling to #37 (17% of sites) in 2006. Further, the FeederWatchers who are still fortunate to host these beautiful birds have seen the average size of grosbeak flocks dwindle in recent years. When grosbeaks were present at a site, the average flock size in New York was 10 birds during the winter of 2005-06, half the size of the flocks reported in the early 1990s. Continent-wide, the same pattern holds. The average number of birds visiting feeders in the east dropped 35% between 1989 and 2006, with dramatic declines also recorded in the central part of the continent and in the west.

On the brighter side, Wilson banded only 30 northern cardinals in eight years, highlighting how rare this species was in New York in the 1950s and 1960s. Since then, this historically southern species has continued to expand its range to the north and can be found at lower elevations throughout New York and southeastern Canada. Cardinals are now one of our more common feeder birds.

Given the widespread downward population trends detected by FeederWatchers, it is unlikely that the missing New York grosbeaks have moved elsewhere. Rather, there are simply fewer evening grosbeaks to be seen. However, the factors contributing to the declining grosbeak populations remain a matter of speculation. One theory suggests that changes in spruce budworm abundance have contributed to the declines (grosbeaks feed the larvae to their young). One thing is certain-data from thousands of FeederWatchers have helped quantify the declines and raise the conservation profile of this species. Further research is required to better understand the changes in evening grosbeak populations and to identify what steps can be taken to bring these birds back to our feeders.

David Bonter works at the Cornell Laboratory of Ornithology, and previously contributed a Conservationist article on Project FeederWatch.

Evening Grosbeak Primer

The evening grosbeak (Coccothraustes vespertinus) is a large, gregarious finch with an unusually bulky bill-once you've seen one, it is difficult to confuse this bird with other species. Grosbeaks are about the same size as a cardinal, but they appear chunkier. Males are a flashy mix of yellow and black with large, white wing patches. Females are duller, but are easily identified by the white wing patches and the large bill. Their raspy, unmusical "kleer" call is frequently given in flight and while feeding.

The breeding range of this finch expanded eastward in the early 20th century to include northern New York and the Adirondacks. Grosbeaks can potentially be seen anywhere in the state in winter with numbers varying considerably from year to year. Birders are most likely to find grosbeaks at higher elevations in coniferous or mixed woods. Although grosbeak flocks are loud and difficult to miss at feeders in the winter, they are remarkably quiet and stealthy during the breeding season. As such, relatively little is known about their nesting habits.

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You don't have to be an expert birder-anyone can help researchers track changes in the abundance and distribution of feeder birds by periodically counting the birds at their own feeders for Project FeederWatch. Cornell will send all of the materials you need to successfully participate, including an identification poster to help you recognize grosbeaks and dozens of other common feeder birds. For more information on how to participate in Project FeederWatch, visit www.feederwatch.org or call the Cornell Lab of Ornithology at 1-800-843-BIRD (2473).

Photo: Andre Dionne