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Last summer the HOOT included a piece on the numbers of hummingbirds coming to member feeders. Using an undocumented guide, it appeared that the six TMBC member stations monitored were feeding close to 6,000 individual hummingbirds per-day in late summer during the height of the southward migration.
Recently, finally, we were able to track down the non-published research data on which the guides were formulated. Now that the resident Anna’s population is at its peak, and as we anticipate the southward migration of other species, here is a simplified look at the basis by which to estimate the number of hummers visiting your feeders each day.
As we know, the best sugar-water formula is 4 cups of sugar to 1 gallon of water. This makes 1.1 gallons of a 20% sucrose solution. This study was done near Nogales, Arizona, in Comero Canyon, where the average hummingbird weighs 3.44 grams. A wild, free-flying hummingbird consumes about 1.5 times body weight per-day of sugar water when feeders are available. This estimate is based on a guess that the birds are getting 70% of their daily energy needs from the feeders while using other sources for their remaining energy needs.
An arbitrary estimate of sugar-water loss of 14% was factored in to account for waste, evaporation, bees, or other birds. To eliminate loss from nectar feeding bats (no such species here), the feeders were taken inside every night. Therefore, 14% was subtracted from the total solution consumed. Now take the average bird weight (3.44 grams) times 1.5 energetic need. This results in 5.16 grams for each bird per-day.
How Many Hummers? When this is converted to ounces, the guide reads: 1 liquid ounce consumed per day = 5.868, 8 oz (1 cup) = 47, 16 oz (1 pint) = 94, 30 oz (1 quart minus) = 176, 48 oz = 281, 96 oz = 563, 128 oz (1 gallon) = 750 hummingbirds!
However, Anna’s Hummingbirds weigh on average 4.266 grams. Thus, 4.3 grams times 1.5 equals 6.4 grams. Divided into 4082 (grams in a gallon), equals 638 Anna’s coming to your feeder. This estimate is of better use until the Rufous, Allen’s, and Black-chinned begin coming through in late summer, for they weigh-in at around 3.4 grams.
During the migration, many Anna’s will be mixed in with these other species. Therefore, at that time, perhaps a 4-gram average weight estimate would be a good factor. Also, do not discount the possibility that these traveling birds may be getting more then 70% of energetic needs from sugar-water feeders.
These researchers are good and know what they are doing. However, the reader will notice my emphasis on guess, estimate, possibility. There were many uncontrolled variables. We will continue our search for additional research data. This summer we’ll be monitoring some of the heavy use stations to develop more local data.
Good Birding.
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