Posted by: Sheri | November 23, 2010

Keeping hummingbird feeders from freezing

Two winters ago I posted some suggestions for helping hummingbirds through winter weather, including boosting the sugar content of the feeder solution, taking advantage of heat radiating from windows, creating shelters, and using heat lamps. A lot of people are dealing with frozen feeders already this season, so here are a few more suggestions gleaned from the winter hummingbird community:

  • Make a “feeder cozy” to help fresh solution retain its warmth longer. It can be as fancy as you like—knitted, crocheted, quilted, down-filled—but pipe insulation (fiberglass wrap or foam tube) or a section cut from a discarded blanket or sweater will do the job. If it’s roomy enough, you may even be able to tuck handwarmer packs inside. [A commenter on BirdForum mentioned using stockings; if your feeder bottle is small enough, a heavy wool sock would make a quick and easy cozy.]
  • Wrap your feeder in outdoor-rated incandescent Christmas lights (the old style, not energy-efficient LEDs). The bulbs should produce enough heat to keep the sugar water slightly above air temperature, especially if you add an outer layer of aluminum foil to reflect heat and block wind.
  • Wrap your feeder in pipe heating tape under a layer of insulation. Thermostatically controlled models will save energy by turning on as necessary to keep the solution just above freezing.
  • Invert your sugars. The freezing point of a solution depends on the number of molecules present. More solute (sugar) molecules make it harder for the solvent (water) molecules to link up. Inverting your sugar, which breaks each sucrose molecule into one of fructose and one of glucose, doubles the number of molecules and depresses the freezing point by a few additional degrees without adding additional sugar.

To invert ordinary table sugar, combine 2 cups sugar with 1 cup water, adding 1/2 teaspoon lemon juice or 1/4 teaspoon cream of tartar to speed up the reaction. Heat the solution to a low boil on the stovetop in a heavy saucepan, washing down the sides of the pan with a little additional water to dissolve any stray sugar crystals. Use a candy thermometer to monitor the temperature, which will rise above the boiling point of water as the water in it boils away. Once it reaches 230° F., remove the pan from the heat and allow the syrup to cool, then pour it into a clean jar, pop on the lid, and store in the refrigerator. Substitute invert syrup for no more than half of the sugar in your feeder solution and reduce the water slightly (by about 2 tablespoons per cup) to compensate for the water in the syrup.

Safety first! Lights and heating tape present fire and electrocution hazards. Use only products that are rated for outdoor use, including extension cords. Do not use electric heating pads outdoors! Don’t enclose Christmas lights inside a cozy or place a cozy-covered feeder too close to a heat lamp—it could start a fire. Heat lamps or Christmas lights may melt the flimsy plastic of discount-store feeders.

Useful links:

Feeding hummingbirds in winter in Indiana

Hummingbird feeder heater using Christmas lights

More on making and using invert sugar from Not So Humble Pie

Related posts:

Helping hummingbirds through winter weather

When the going gets chilly, the chilly get crafty

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Responses

  1. Let me underscore Sheri’s admonishment, that the syrup should not be warm to the touch, much less steaming (I’ve seen that!). If the syrup is mixed at 1:3, it won’t freeze unless it falls below 20°F, so 25 or 30 is plenty.

  2. Where do hummingbirds spend the night in the freezing temperatures of the Northwest? Do they protect themselves in dense folage or just perch on a branch, or do they go to a nest? Our nights are freezing and we have had three Anna’s coming to our feeder for over a month. Trying to help them by keeping the feeders unfrozen and filled. Thanks, Karen Warberg

    • Like most birds, hummingbirds roost under dense foliage for protection from cold and/or wet weather. Some birds whose nests are enclosed do use them for winter shelter (Bushtits, many cavity-nesting birds such as bluebirds), but open-cup nesters such as hummingbirds generally use the nest only as a nursery. Female hummingbirds have to stay on their nests overnight even through bad weather, but in colder climates they choose a well-protected nest site to minimize heat loss and exposure to rain and/or snow.

  3. Nice! Physical chemistry on a bird blog. I loved P Chem in high school. The additional problems that I see. 1) If the bird with the small brain did not leave when it should have, it needs a suitably warm habitat, with not only sugar, but protein as well. 2) If you can manage that, it must not kill itself by flying into your window. 3) Your cat (or neighbors cat) can’t catch it. 4) Hummingbirds are so small that there energy can’t last long. Their energy is lost at a rate that is more than linear with the difference between their body temperature (they are warm-blooded) and ambient temperature. If they are to survive a very cold night, they may very well need to eat at night. So they must nest in a nest that is relatively warm, close to wear they feed, and be able to fly to the feeder. Lights?

    • 1a) Hummingbirds have larger brains in proportion to body size than we do (~3.8% of body mass vs. ~2% in humans [Rehkämper et al. 1991]).
      1b) Both the original post and this one are concerned primarily with extreme weather conditions in places where hummingbirds are normally year-round residents.
      1c) Arthropods are available even in winter – just ask a chickadee.
      2) Not a winter-specific problem, and hummingbirds are less vulnerable to window collisions than most other birds. Placing feeders close to windows reduces the risk and severity of collisions and takes advantage of heat radiated through the glass to keep the feeder thawed.
      3) A big problem, but also not specific to winter (or to hummingbirds).
      4a) Short days/long nights are definitely a problem at higher latitudes, but night feeding has been reported.
      4b) Hummingbird nests are nurseries, not shelters. You mean “roosts,” and wintering hummingbirds do tend to favor yards with dense shrubbery that provides sheltered roosting locations.
      4c) Use of lights is discussed in the original post on this topic.

  4. Research has shown that ratio of water to sugar should be 4:1 and no greater. The greater ratio harms their kidneys & cannot be slurped up through their grooved tongues. PLEASE do not increase ratio; keep it sat 4:1; bring feeders in at night, heat them or just don’t feed but do no harm is what to live by

    • Marganna, I know you mean well, but you’ve been misled.

      As I mentioned in this earlier post, it’s true that higher viscosity reduces hummingbird feeding efficiency, though this occurs at sugar concentrations higher than 3:1 (~21-23% sugar by weight) even at low temperatures (Tamm and Gass 1986, Nicolson & Thornburg, Fig. 1).

      Though I’d love to see citations for research that supports the kidney claim, I won’t hold my breath. Why? Because I’ve been scouring the scientific literature on hummingbirds and talking to fellow hummingbird researchers for close to 25 years and have failed to find any evidence that stronger sugar solutions are harmful to hummingbirds’ kidneys (or livers, which is the more common claim). What I have found is abundant research and historical precedent supporting flexibility in the recipes we use to fill our feeders.

      If sugar concentrations stronger than 4:1 were harmful to hummingbirds, many of the flowers they feed on would be killing them with too-sweet nectar. Natural nectar produced by hummingbird-pollinated flowers varies from under 5% sugar by weight (weaker than 15:1 by volume) to over 50% (stronger than 1:1 by volume). Both the “standard” 4:1 solution by volume (~17-19% sugar by weight) and a 3:1 solution are weaker than the average sugar concentration of 255 species of hummingbird-pollinated flowers from throughout the Americas (25%, ~5:2 by volume; Nicolson and Fleming 2003). Many of the most popular flowers planted for hummingbirds produce nectar significantly stronger than 4:1 (Demcheck 2003), and sugar concentrations can vary among different plants of the same species, among different flowers on the same plant, and by elevation and time of day (Cruden et al. 1983).

      That said, the “traditional” 4:1 recipe (which was almost unheard of before 1970) has a few advantages over stronger solutions for average hummingbird enthusiasts, the birds, and our shared environment, including:

      * It’s easier to remember and use a single one-size-fits-most recipe than to go back and forth between two (or more) recipes.

      * It meets the birds’ water needs at slightly higher temperatures than 3:1 (Calder, W.A. III and S.M. Hiebert. 1983. Nectar-feeding, diuresis, and electrolyte homeostasis in hummingbirds. Physiological Zoology 56:325-334.).

      * The birds will have to visit the feeder more often to meet their energy needs, resulting in more feeder activity (purely selfish, but that’s why we feed hummingbirds).

      * Lower sugar concentrations are less likely to disrupt local ecosystems by distracting the birds from wildflowers that need their pollination services.

      Of course, the average hummingbird enthusiast doesn’t feed hummingbirds in sub-freezing weather, when the birds’ water needs are low, bees aren’t active, and wildflowers aren’t blooming. As I explained in this post, a 3:1 solution not only stays liquid at lower temperatures but allows the birds to feed more efficiently, which may mean the difference between life and death for a cold-stressed hummingbird. In a laboratory experiment, Rufous Hummingbirds exposed to four hours of near-freezing temperatures lost weight when drinking a 15% (~5:1) or 20% (~4:1) sugar solution but maintained or gained weight when drinking a 30% solution (~2:1; Gass, Romich, & Suarez 1999).

      It’s a minor point, but you’re also a bit behind the times on what we know about how hummingbirds’ tongues work. It’s been known for decades that they don’t use their tongues to “slurp” (suck) nectar as through a drinking straw, but recent research using high-speed video has shown that the main mechanism involves the “grooves” in the sides of the tongue opening automatically when immersed in liquid and closing to capture it as the tongue is retracted.


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