mjm@oliven.olivetti.com (Michael Mammoser) (02/05/91)
Recently the question came up about leaving hummingbird feeders up past a certain date because of the alleged affect it might have on influencing their migration; a question that has come up a number of times in the past. All of the "authoritative" references that I have seen or heard indicate that the idea of feeders negatively influencing migration is a myth. I even posed the question to a professional ornithologist, who dismissed it as untrue. It occurred to me that some hard data, that could shed some light on the issue, might be available. A local biomonitoring research facility, Coyote Creek Riparian Station, does year-round bird capture and banding; including hummingbirds. The capture data from CCRS could be directly applicable to the question at hand for a number of reasons. A large variety of hummingbirds are represented in the data; including year-round resident species, migratory species, and migratory-resident species. Hummingbird feeders are maintained year-round as an attractant to these birds. The relatively mild winter weather would allow influenced birds to survive, thereby increasing the chances of them being captured and appearing in the data base. The following charts show the hummingbird capture data for the previous two years, on a month-by-month basis. The following legends apply: ANHU - Anna's Hummingbird. Local year-round resident. BCHU - Black Chinned Hummingbird. Local migratory resident. ALHU - Allen's Hummingbird. Local migratory resident. CAHU - Calliope Hummingbird. Local migrant. RUHU - Rufous Hummingbird. Local migrant. COHU - Costa's Hummingbird. Local vagrant. 1989 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total BCHU 6 9 2 6 26 13 1 63 ANHU 10 4 9 15 24 42 54 54 15 7 12 5 251 CAHU 3 1 1 5 RUHU 9 94 5 4 14 23 10 159 ALHU 4 12 10 14 10 2 10 3 65 1990 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total BCHU 5 8 7 8 3 31 ANHU 6 2 2 10 9 37 43 40 12 6 4 4 175 COHU 1 1 CAHU 1 1 2 RUHU 11 24 2 3 5 45 ALHU 2 5 7 4 11 8 7 1 45 Other than the single Black Chinned Hummingbird captured on 12 OCT 89, no migratory hummingbirds were captured during the months of October, November, December, or January. In fact, all of the migratory hummingbirds show clearly defined time periods representing their presence locally, outside of which, they just aren't found. Although it is difficult to predict the behavior of any individual bird, and extrapolating this information to cover species not in the data base may be somewhat speculative, I think this data goes a long way toward supporting the idea that hummingbird migration is not, in general, influenced by the presence of feeders. Mike