Three species of hummers normally prevalent in Summit County, Colorado during June, July and August appeared in far fewer numbers this year.
Broad-tailed Hummingbirds, which nest in Colorado's high mountains and Rufous Hummingbirds, which migrate through the same area on their path south to Mexico were conspicuous by their absence in 2011. Calliope Hummingbirds, though much more rare than the other two species, were not seen at all in areas where they have been recorded for at least two years.
Much of Summit County, a skiing destination just 70 miles west of Denver, lies at elevations of 9,000 feet and more. During the summer months of June, July and August of 2009 and 2010, birders staying at the ski resort of Keystone observed heavy populations of Broad-tailed and Rufous Hummingbirds, as well as the rarer Calliope Hummingbird, which accounted for perhaps five percent of hummingbird sightings.
Broad-tailed Hummingbirds winter in Mexico as do the other two species, but while Rufous and Calliope Hummingbirds travel much farther north to the Pacific Northwest, British Columbia and Alaska to nest, the Broad-tailed Hummingbirds nest in high-elevation sites including Colorado. Rufous and Calliope Hummingbirds return to their wintering sites in Mexico beginning in early summer, and many of these birds cross Colorado, pausing in the high country to refuel. All three birds are attracted to high mountain wildflowers, such as Scarlet gilia, to sapsucker wells and to artificial feeders which are hung by local residents and summer visitors alike.
Evidence of Reduced Hummingbird Numbers in 2011
The author spent approximately one month in Keystone and the surrounding Summit County area in each of the past three years, hanging and observing multiple hummingbird feeders, as well as interviewing local residents and other visiting birders on extended vacations. While it was immediately obvious in 2011 that hummingbird numbers were down, the most telling proof was the drop in sugar water consumption. In the summer of 2010, two-cup (16-ounce) sugar water feeders were depleted in two days or less, regardless of the number of feeders offered, and this continued throughout the three summer months of 2009 and 2010. During two months of observation from mid-June through mid-August of 2011, however, these same capacity (and roughly the same number of) feeders in the Cinnamon Ridge Condominium complex in Keystone still contained some food after two weeks. This consumption ratio suggests the number of feeding birds in 2011 dropped seven-fold.
When hummingbird populations are high, birds appear to be less timid and aggressive, sharing feeders more and feeding from hand-held feeders. Seven or eight hummers were often seen on a single feeder in 2009 and 2010, and a hand-held feeder would not discourage the birds. In comparison, in 2011 it was rare to see even two birds on one feeder, and the birds were especially wary of nearby humans.
Field trip observations appeared to confirm those made at artificial feeders. Trips to Chihuahua Gulch, where active sapsucker wells and Broad-tailed and Rufous Hummingbirds have been found in earlier years, discovered no active wells, only an occasional Broad-tailed Hummingbird and, for that matter, no Red-naped Sapsuckers. Coincidentally, Red-naped Sapsuckers were commonly found around Keystone (a lower elevation), where they were a rarity in the two prior years. This suggests a possible retreat to lower elevations for a number of birds, and in fact field observations found far fewer birds of all types at higher elevations in 2011. A similar lack of hummingbirds were found on other field trips in Summit County, including Shrine Ridge, Lower Cataract Lake, Rock Creek and Spruce Creek.
Possible Reasons for Fewer Colorado Mountain Hummingbirds in 2011
To the author's knowledge, no studies or explanations have been offered regarding declining hummingbird numbers in 2011, although weather may well be a contributing factor. Northbound hummingbird migrants encountered abnormally severe cold weather in Arizona in early February, 2011. Temperatures in the typically mild winter in and around Tucson, for example, plunged to record lows of 13-17 degrees on two consecutive days, February 3 and 4. Many resident and migrating hummingbirds were impacted by this freeze, likely including all three species of Summit County's birds, and it is probable that higher than normal hummingbird mortality resulted.
According to Summit County residents, an unusually late snowfall occured in the area in May, and much more snow than normal was still evident on the surrounding mountains during the summer months. This late and heavy snow, together with heavy early summer rains may have impacted migrating bird numbers and also may be partly responsible for fewer birds having been observed at higher elevations this summer.
Hopes that the 2011 Decline in Colorado Mountain Hummingbirds is an Anomaly
Fewer hummingbirds observed in Keystone in July and August may result in lower numbers of observed birds in Arizona in August and September, as the migrating birds move south. However, hummingbirds are as tough as they are beautiful. Barely weighing as much as a penny, many North American hummers fly 2,000 miles or more between central Mexico and southwestern Alaska, and their ability to induce torpor helps them survive abnormally cold weather. Hopefully, 2012 will mark a return to high hummingbird numbers in Colorado's Summit County.
source: www.suite101.com
