Beet juice in hummingbird feeders? NO!

In Arizona’s White Mountains, hummingbird swarm a feeder filled with colorless sugar water. Coloring of any kind is unnecessary, and the quantities hummingbirds consume increase the health risks of artificial dyes.

A colleague recently contacted me via Facebook to ask if beet juice might be safe if used to color sugar water in hummingbird feeders. I made the mistake of saying “probably” before doing enough research. After reading up on the nutrients found in beets, I’ve got to say “NO!

For decades, hummingbird experts have denounced artificial dyes as unnecessary, unnatural, and potentially harmful, but it’s tough to override the public image of a feeder filled with jewel-like red liquid. As frustrating as it is to see people still coloring their feeder solutions, it’s encouraging that some are looking for benign alternatives to artificial dyes.

The natural coloring I usually recommend is a few drops of raspberry, cherry, or cranberry juice. The pigments in these fruits are antioxidants called anthocyanins. Beet pigments, called betalains, are also antioxidants and are found in cactus fruits and pollens, so they’re something hummingbirds might ingest naturally (though in vastly smaller quantities than they’d get from a regular diet of beet-red sugar water). The problem is that beets are also a good source of iron. That’s not a problem for most humans, but it is for hummingbirds and other nectarivorous birds, as I explained in Feeder Solution Evolution Part I. Vegetable-based dyes made from beet pigments are purified, so you wouldn’t expect much iron to remain. Just juicing or boiling beets runs the risk of extracting deadly iron along with desirable pigments.

Even without the iron issue, there’s a potential stumbling block in the unsubstantiated/undebunked rumor that hummingbirds don’t like beet sugar. If that’s true, then they almost certainly wouldn’t like beet juice, either, since it would contain far higher concentrations of the bitter-tasting saponins blamed for this reported preference.

A Viceroy enjoys the juice of an Englemann’s Prickly Pear fruit.

The good news is that the betalain-rich fruits of some prickly pear cacti (called tunas in Spanish) are much lower in iron than beets (Englemann/Lindheimer Prickly Pear found over most of the Southwest. If you’re lucky enough to live where this species is native, you can harvest ripe tunas using barbecue tongs. Wash thoroughly (wear gloves!) before cooking or juicing to remove dust and spines, and filter the resulting juice to remove any stray spines and other solids that might contribute to fermentation of your sugar water.

The juice will keep over the winter if you freeze it in ice trays and store the cubes in plastic bags in the freezer. Then it’s easy to pop a cube into a fresh batch of sugar water (make large batches or use small cubes—it doesn’t take much to give the liquid a bright color). You can also use the juice to make jelly and syrup, color and flavor lemonade and gelatin, or add a desert touch to your Thanksgiving celebration.

One last issue with betalains in hummingbird feeder solution is that they might perform differently depending on the quality of the water used. These pigments are pH sensitive, turning reddish in acidic solutions and bluish in alkaline ones just like litmus paper. If added to normal tap or bottled water, which is typically neutral to slightly alkaline, prickly pear juice will turn purple to violet. It won’t matter to the birds, of course, but it might take adding a few drops of lemon juice to the solution to get a color similar to that produced by artificial dyes.

What a lot of trouble. Why not stick to plain sugar water?

Related posts: Beet sugar: Maybe a myth, but not debunked Search of the Week: “is molasses ok to feed hummingbirds” Search of the Week: “if refined sugar is so bad for us, then why do we feed it to hummingbirds??” Feeder Solution Evolution Part I: The basics

Search of the Week: “can i give hummingbirds mountain dew?”

Answer:


Seriously, why would someone even think of doing that?

Beet sugar: maybe a myth, but not debunked

The latest edition of BirdWire, the monthly electronic newsletter published by Bird Watcher’s Digest, features longtime contributor Kevin Cook busting bird myths. Naturally, I had to click the link to see if Kevin tackled any hummingbird myths. He did, but…

The “myth” he took on is about beet sugar. Some hummingbird aficionados use only cane sugar because they claim the birds can tell the difference. I’m not convinced that this is true, so I was excited about the prospect that someone had conducted field tests to demonstrate that hummingbirds have no preference. Unfortunately, Kevin based his debunking on much flimsier evidence. He wrote:

Kitchen research in which neither cooks nor overseeing researchers knew whether they were using beet or cane sugar repeatedly showed no difference in the outcome of desserts based on the origin of the sucrose.

Taste buds, whether hummingbird or human, cannot tell beet sugar from cane sugar.

Brown Violetear

Gratuitous hummingbird photo (because I know what you crave).

Wait… what? Humans are humans, and hummingbirds are hummingbirds. There’s even a significant difference within our own species in the density of taste buds and the sensitivity to strong flavors (look up supertasters). Unless you’re putting liquified tiramisu in your feeders, how the two sugars perform in desserts has no bearing whatsoever on how hummingbirds perceive them.

What we need (and still don’t have) to debunk this myth (if myth it is) is a double-blind study presenting the birds with solutions of the same concentration in similar feeders in randomized positions, etc.

Sounds like an excellent science fair project.

When the going gets chilly, the chill get crafty

hand-crocheted humingbird feeder cozy

My hand-crocheted hummingbird feeder cozy

After posting a bunch of second-hand/theoretical advice for keeping hummingbird feeders from freezing, I found myself and my clientele (several Anna’s and a Violet-crowned or two) facing a forecast low of 13º F. (-10º C.). My northern friends will smirk (and rightly so), but this is southern Arizona for peeps‘ sake.

Since temperatures this low are such a rare event here, insulating the feeder seemed like the most sensible (and cheapest) approach. Besides, my crochet hooks had been collecting dust since last fall, and this was a good excuse to get back to hooking. So to speak.

After a quick stop to shop for appropriately colored yarn and about two hours of hooking, unraveling, and rehooking, I had a crocheted feeder cozy for an 8-oz. Nature’s Best (my all-time favorite bottle feeder that’s no longer available, sadly).

Before calling it a night, I filled a clean feeder with hot 3:1 solution, slipped on the cozy, and stumbled across the starlit yard to hang it in one of the more popular spots. Another Nature’s Best that had been out all day had frozen beyond the Squishee stage already, with a band of syrup trapped between solid layers of ice.

When I finally got around to checking the feeder this morning (about an hour and a half after sunrise), there was no ice in the bottle at all, but swirls of denser syrup indicated that at least some of the solution had frozen. Interestingly, the HummZinger Mini hanging in front of the poorly insulated living room window showed no signs of having frozen, despite containing a smaller volume of solution with larger surface area and getting very little morning sun to warm it up (it’s on the north side of the house).

I was a little worried about how the hummingbirds would respond to the weird appearance of their feeder. The female Violet-crowned Hummingbird didn’t seem the least bit put off by the bright red “sweater,” but then she didn’t have to wear it.

Related posts:

Keeping hummingbird feeders from freezing

Helping hummingbirds through winter weather

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

Search of the Week: “why don’t hummingbirds get diabetes”

A male Broad-billed Hummingbird threatens an intruder in his feeding territory.

A male Broad-billed Hummingbird threatens an intruder in his feeding territory.

This week’s featured search topic has been addressed on LB&E previously here and here.

Type 2 diabetes, the disease people are thinking of when they ask such questions (because they’ve been told, wrongly,*⇓ that sugar consumption causes diabetes), is largely a modern human affliction. We eat too much, including highly processed foods full of easily digested simple carbohydrates that flood our bloodstreams with glucose. We exercise too little, contributing to getting fat and staying fat. Our bodies may continue producing insulin to aid in utilization of the glucose in our systems, but over time our cells may stop responding to it.

These issues weren’t much of a problem for our pre-industrial ancestors (even those with a genetic predisposition to diabetes), and they’re still not much of a problem for people living labor-intensive lifestyles and eating traditional diets high in complex carbs, fiber, and other good things.

They’re also not a problem for hummingbirds. More than 40 million years of evolution have adapted these tiny, hyperactive dynamos to a sugar-rich diet. To maintain some of the highest metabolic rates ever measured, hummingbirds must take in enormous amounts of energy. The most energy-dense food available to them is flower nectar. Without it, the tiny, hovering jewels we know and love would never have evolved.

You might say that hummingbirds show three classic symptoms of diabetes: they eat a lot (polyphagia), drink a lot (polydipsia), and pee a lot (polyuria). Of course, these “symptoms” are simply consequences of a high metabolism and water-rich diet. They also have very high blood glucose levels, high enough to cause serious complications in humans, but their absorption and utilization of the sugars in their diet are so efficient that almost none ends up in their urine (as it does in human diabetes patients).

Medical researchers would love to know exactly how hummingbirds avoid the short-term and long-term complications of high blood glucose, but it’s clear that their ability to do so has been honed by natural selection. Any hummingbird that had a serious defect in its ability to absorb and/or metabolize sugar would be dead within days, weeded out of the gene pool.

Here’s an in-depth examination of the issues from the perspective of human health:

Adipose energy stores, physical work, and the metabolic syndrome: lessons from hummingbirds

* Since this post was written, new research has persuaded many members of the medical community that there’s a more direct link between sugar consumption and Type 2 diabetes than decades of propaganda by Big Sugar would have us believe.

Feeder Solution Evolution Part I: The basics

The posts lately have been hummingbird heavy, but you can blame the time of year. Both southbound migrants and a few remaining locals—Rufous, Broad-tailed, Black-chinned, Anna’s, Broad-billed, an occasional Calliope, Costa’s, or Violet-crowned, and our yard’s first Lucifer—have been shrieking and jousting outside my living room window every daylight hour, so it’s hard to think about anything else (which makes it hard to get any real work done but also keeps my mind off things I’d rather not dwell on).

This is going to be a heavy post, so I’m dividing it into three parts. If all you’re interested in is what you should/shouldn’t put in your hummingbird feeder, you needn’t read any further than the end of this installment. If you’re curious about how these recommendations came about—the science and history behind them—I hope you’ll come back or click through to read the second and third installments.

Let’s kick things off with something happy. Happy, happy, happy. No stress, no angst.

A young White-eared Hummingbird drowses in the sun

A young White-eared Hummingbird drowses in the sun.

Okay, down to business. At the request of my friend and colleague Laura Erickson, who writes and edits for the Cornell Laboratory of Ornithology, I’m finally tackling this long-neglected and often controversial topic. Here is what you need to fill your hummingbird feeder:

1. White sugar.

  • Sucrose (a.k.a. white table sugar) is the main sugar in the sap of plants and also in the nectar of hummingbird-pollinated flowers (1). We squeeze sugar cane and sugar beets to get our sucrose, and hummingbirds drink nectar, sap, and properly made feeder solutions to get theirs. It does not give them diabetes. It will not rot their teeth.
  • If ordinary granulated sugar doesn’t dissolve fast enough for you, and you don’t mind trading cost for convenience, buy superfine baker’s or caster sugar instead (but not powdered sugar, which contains anti-caking agents).
  • Though pure cane sugar is often recommended over pure beet or blended sugar (which is usually labeled simply as “sugar”) based on the perception that it tastes better to the birds, it takes sophisticated testing for food scientists to distinguish between them. Sugar cane yields somewhat more sugar per acre than sugar beets but uses much more water, displaces more biodiversity, and has to be transported farther (at least in U.S. markets), so beet sugar may be the “greener” choice.

2. Good-quality water.

  • If there’s any reason that you don’t personally drink your tap water (too many minerals, has a funky taste or smell, tested positive for pollutants, etc.), don’t make your hummingbird guests drink it, either. If it’s discolored by iron, you definitely shouldn’t use it to make feeder solution (see the second bullet point under the “don’ts” below).
  • Researchers have determined that hummingbirds’ kidneys are incredibly good at getting rid of water without losing their bodies’ electrolyte salts (2), which clears the way for feeder solutions made with water purified by reverse osmosis or distillation. Water softened by ion exchange is high in sodium, and overloading the birds on sodium may not be a good idea.

Sugar. Water. That’s all you need. Really.

The list of things you should not put in your hummingbird feeder is a wee bit longer:

  • Honey. It’s a natural food, but only if you’re a honeybee. Bees start with the nectar of flowers not typically used by hummingbirds, modify it with digestive enzymes, then barf it back out and evaporate off most of the water. The final product contains less palatable sugars plus stuff you seriously don’t want to feed to hummingbirds. Once diluted to feeder strength, honey becomes an ideal food for a variety of microbes, including some that can cause disease. Honey-water diets have been linked with fatal yeast infections (candidiasis) in captive hummingbirds (3), and similar infections have been reported in wild ones. Honey belongs on your biscuits, not in your feeders.
  • Brown or even brownish sugar. The color derives in part from iron, for which nectarivorous and frugivorous birds have a very low tolerance (4,5). Even a little extra iron over time can build up to lethal levels in the birds’ bodies. Refined white sugar has had the trace iron removed to make it a more attractive product, which incidentally makes it safer for hummingbirds. Unfortunately for those of us who try to shop green, organic sugar is typically not fully refined to pure sucrose, so it’s not safe. Rumors of problems at tropical feeding stations may be related to the use of lightly refined turbinado (“raw”) sugar containing iron, but these reports have yet to be substantiated.
  • Artificial coloring. The vast majority of hummingbird flowers put the color on the outside, not in the nectar. FD&C Red #40 and #3, the dyes used in most “instant nectar” products and the food coloring in your pantry, are like nothing the birds would ever encounter in nature. They may not be dangerous at human consumption levels, but hummingbirds can drink more than 5 times their weight in liquid in a day. Medical research has linked large dosages of these dyes to a number of serious health problems. Backyard comparisons also suggest that the birds don’t like the way these dyes taste. If colorless sugar water just doesn’t look right to you, use a few drops of fruit juice concentrate to tint it.
  • Artificial and non-nutritive sweeteners. This includes saccharin (Sweet’N Low®), aspartame (Equal®, NutraSweet®), sucralose (Splenda®), stevia (Truvia®, PureVia®), monkfruit or lo han (Nectresse®), acesulfame potassium (acesulfame-K), erythritol, and xylitol. Hummingbirds need the calories. If they get fat, it’s for a good reason, and they won’t stay that way for long (unlike us big sluggish primates.)
  • Commercial “instant nectar” and “hummingbird food” products. Most contain unnatural additives such as dyes, preservatives, and/or flavors that, despite what manufacturers and retailers may claim or imply, have never been tested or approved as safe for hummingbirds. Those products without additives are basically overpriced boxes of extrafine white sugar (see the second bullet point under “White Sugar” above).
  • Nutritional supplements. The nectar of hummingbird flowers is little more than sugar water anyway (1), and anything else you add can cause premature spoilage and other problems. This includes commercial diets for captive hummingbirds, protein powder, fruit juice (except a few drops of concentrate to add a little color), Jell-O, Gatorade, Mountain Dew, vanilla extract, and strawberry daiquiri mix. Hummingbirds are really efficient hunters, even in winter, but if you want to supplement their protein/vitamin intake, raise fruit flies in jars or start a compost pile. For minerals during nesting season, offer clean ashes from natural wood (no synthetic logs, paper, trash, etc.).

See this post for a more comprehensive list.

Now that we have the two ingredients, the next step is determining what proportion to mix them in. Though opinions about feeder solutions vary slightly within the hummingbird community, most hummingbird experts still endorse this recipe:

4 parts water

1 part sugar

Good old 4:1 has proven itself safe and effective over more than four decades of use, it’s well within the range of sugar concentrations found in the nectar of hummingbird pollinated flowers (1), and, like a one-size-fits-most garment, it leaves enough “wiggle room” to accommodate some challenging environmental conditions without short-changing the birds on either energy or water. Hardcore hummingbird fanatics may have sound reasons for using slightly stronger or weaker solutions, but all the average hummingbird host needs to remember is 4 parts clean water + 1 part white sugar.

Stay tuned for part II, the science behind hummingbird feeder solutions.

Resources for this post:

1. Nicolson, S. W. and P. A. Fleming. 2003. Nectar as food for birds: the physiological consequences of drinking dilute sugar solutions. Plant Systematics and Evolution 238(1-4):139-153.

2. Lotz, Chris N. and Carlos Martínez del Rio. 2004. The ability of rufous hummingbirds Selasphorus rufus to dilute and concentrate urine. Journal of Avian Biology 35(1):54–62.

3. Orr, K.A. and M. E. Fowler. 2001. 18: Order Trochiliformes (Hummingbirds). In Biology, Medicine, and Surgery of South American Wild Animals, Murray E. Fowler, Zalmir S. Cubas Eds. Iowa State University Press, Ames, Iowa.

4. Frederick, H., Dierenfeld, E., Irlbeck, N., and S. Dial. 2003. Analysis of nectar replacement products and a case of iron toxicosis in hummingbirds. In Ward, A., Brooks, M., Maslanka, M., Eds. Proceedings of the Fifth Conference on Zoo and Wildlife Nutrition, AZA Nutrition Advisory Group, Minneapolis, MN.

5. Ketz-Riley, C.J. and C. Sanchez. 2015. Chapter 26: Trochiliformes (Hummingbirds). Pp. 209-213 in Fowler’s Zoo and Wild Animal Medicine, Volume 8, R.E. Miller, M.E. Fowler eds. Elsevier (Saunders).

Related posts:

Search of the Week: “if refined sugar is so bad for us, then why do we feed it to hummingbirds?”

Search of the Week: “is molasses ok to feed hummingbirds”

Beet juice in hummingbird feeders? NO!

Search of the Week: “can I give hummingbirds mountain dew”

Perch hypothermia rides again

You cannot reason a person out of a position he did not reason himself into in the first place.

— attributed to Jonathan Swift, 1667-1745

It was too good to last. After four years of keeping under the radar, Montana wildlife rehabilitator Judy Hoy is once again warning the public about the evils of perches on hummingbird feeders.

Briefly, Hoy believes that hummingbirds that perch to feed on cold sugar water are at risk of hypothermia. From her recent article in the Great Falls Tribune:

If the outside temperature is below 50[° F.] and the sugar water is cold, the birds can become completely hypothermic after drinking two crops full without flying. They then fall to the ground and eventually die from cold and lack of food or are eaten by magpies, cats or other predators.

Hover-feeding isn’t a problem, she says, because the muscle action helps to warm the bird’s body.

She claims that hummingbirds, especially Rufous, are “dying by the thousands every spring” from this phenomenon and is understandably frustrated that hummingbird researchers, feeder manufacturers, and government agencies won’t take her seriously. In this latest article, our self-styled Cassandra gets a little testy:

You may get the impression from this post that I am running out of patience with stupidity and I am!

Same here, Judy.

By her own account, Hoy started her anti-perch campaign in 1985. A quarter of a century is plenty of time to gather an enormous amount of support for her claims, so where is it? Despite repeated requests from skeptics, she hasn’t produced any photos, videos, necropsy results, or other objective evidence to demonstrate that feeder perches cause hypothermia in otherwise normal, healthy hummingbirds. Instead, she continues to rely on anecdotes, opinions, and misinterpretations of cherry-picked scientific research, ignoring more relevant research that refutes her claims.

Over the same 25-year period, people who host wintering hummingbirds have amassed hundreds of thousands of observations of birds perching to feed when the temperatures of both the air and the sugar water are well below freezing (20 degrees or more colder than Hoy’s hypothetical hypothermia threshold), and showing absolutely no ill effects. Additionally, hummingbird banders in the southeastern U.S. have documented hundreds of hummingbirds, including Rufous and Calliope, returning year after year to the same wintering sites. Many of these birds take their first sips of frosty sugar-water every winter morning while resting on feeder perches. Though this doesn’t “disprove” Hoy’s perch hypothermia claims, it does strongly suggest that it’s at worst an extremely rare cause of mortality.

Anna’s Hummingbird in my southeastern Arizona yard on a snowy day

None of this seems to make a dent in Hoy’s belief. She responded to these challenges by adding increasingly elaborate and often conflicting justifications for the lack of independent verification: most people never see hypothermic hummingbirds because predators get them first, it happens mostly in “Canada, North Eastern States and…Western Montana,” Rufous are particularly cold-sensitive (!), different species have significantly different “thermodynamics,” pesticides and herbicides sprayed in her area damaged their mitochondria and/or thyroid function.

Unlike Hoy, I don’t expect anyone to take my word on something without evidence. That’s why I wrote a detailed analysis of perch hypothermia way back in 2006, after a message she posted to an online discussion group was forwarded to other groups by well-meaning participants. At Hoy’s request, I sent her all of the evidence refuting her claims, with faint hope that we might lay perch hypothermia to rest once and for all. No such luck. Like True Believers® in so many other crackpot ideas (young-earth creationism, alien abductions, “rods,” homeopathy, etc.), Hoy’s faith is unshakable.

The latest version of her story adds a new and ominous detail, but one that’s easily debunked. In the Great Falls Tribune article, she says:

…Rufous and Calliope are now on Audubon’s red list.

Nope. Both species were listed on the 2002 Audubon Watchlist as yellow (declining), not red (declining rapidly). The 2007 Watchlist includes only the Calliope, still in the yellow category. It’s disappointing, but far from surprising, that even her “new” information is both overstated and outdated.

Removing perches from hummingbird feeders is unlikely to do any significant harm, but it’s equally unlikely to do any significant good. Birds need well-informed friends to help protect them from real and growing environmental threats, so I hate to see the same alarmist claptrap making the rounds over and over and over. Cut the perches off your feeders if you like, but don’t let misinformed prophets of doom distract you from doing things that actually help hummingbirds:

And if you’re still worried about “perch hypothermia,” make your feeder solution richer (3:1 instead of 4:1) during cold weather so that the birds have to take in less cold solution to get the same amount of energy.

Helping hummingbirds through winter weather

With the usually temperate Pacific Northwest battered by fierce winter storms, there’s a lot of concern about how the resident Anna’s Hummingbirds are handling brutal temperatures and frozen feeders, and what their human hosts can do to help them survive.

One way to help is to use a slightly stronger feeder solution. Many people, myself included, have switched to a ratio of 3 parts water to 1 part sugar for all or most of the year. The sugar concentration (about 23% by weight) is closer to the average sugar content of hummingbird flower nectars (about 25%) than the standard 4:1 recipe (about 18%), and it has the advantage in winter of freezing a little more slowly.

It’s important not to go overboard, because more is not necessarily better. Sugar solutions sweeter than 3:1 can be syrupy enough to interfere with feeding efficiency, and this effect is magnified as temperatures plunge. There’s also the issue of dehydration, since nectar is a hummingbird’s main source of water (especially when everything else is frozen).

Even 3:1 will freeze if the temperatures dip low enough, but some winter hummingbird hosts have reduced the need for switching feeders by placing them next to a window (the more poorly insulated the better), inside an open shelter made of plywood, or under an outdoor-rated heat lamp.

If you make the switch to 3:1, you’ll need to adjust your expectations a bit. Since it contains more calories per drop than 4:1, your birds will not have to visit as often. It may look as though they’re avoiding the feeder when actually they’re just feeding more efficiently.

Related posts:

Keeping hummingbird feeders from freezing

When the going gets chilly, the chill get crafty

Rethinking winter hummingbirds

Keeping hummingbird feeders from freezing

Do we see what bees see?

Trans-Pecos Morning Glory

Trans-Pecos Morning Glory

Featured in The Open Laboratory 2008!space

If you’re a hummingbird gardener, you’ve probably developed a search image that helps you select flowers most likely to please your discriminating clientele. Essentially, you’re thinking like a hummingbird, associating trumpet-shaped blossoms in “hot” colors with the promise of a sweet reward. Most hummingbird feeders are based on similar visual cues, but what if your feeder sent mixed signals that unintentionally lured less welcome critters as well as hummingbirds?

I first began to ponder this issue twenty years ago, when I was co-manager of The Nature Conservancy’s Ramsey Canyon Preserve. The preserve was having a lot of trouble with bees, mostly long-tongued bumblebees and carpenter bees, on some of its twenty-odd feeders, mostly the Perky Pet 210-P and similar models with yellow plastic “flowers” around the ports.

As I read everything I could find about hummingbirds, including pollination ecology, it dawned on me that very few hummingbird-pollinated flowers are yellow and very few bee-pollinated flowers are red. A little reading confirmed that yellow is a color ecologists associate with flowers that are insect pollinated (entomophilous, “insect-loving,” as opposed to ornithophilous, “bird-loving”). And there’s shape, too. Those five-petaled plastic pinwheels around the feeder ports could stand in for the flowers of any of hundreds of species in the sunflower family. And who pollinates those little yellow sunflowers? Bees and other six-leggity beasties, that’s who.

Since the preserve’s bookstore sold hundreds of Perky Pet feeders every year, I called the company to ask if they could make us a few red plastic flowers using the same mold as the yellow ones. A few weeks later a box arrived containing several hundred red plastic flowers. I immediately grabbed a handful and used them to replace half the yellow flowers on a couple of the problem feeders. The results were unambiguous: The bees would fly up to the red side of the feeder, buzz around, maybe land briefly, but soon take off and fly around to the other side to join their hive-mates feeding around the yellow flowers. Very few remained at the red flowers long enough to discourage hummingbirds from feeding. This continued for a couple of weeks, well beyond the time it should have taken for the bees to learn to associate the red “flowers” with food.

It was out with the yellow and in with the red on of all the preserve’s Perky Pet feeders. The leftover red flowers we handed out to preserve visitors having bee problems with similar feeders. Eventually we phased out Perky Pet feeders altogether (even in the bookstore), but until then this strategy helped to reduce the preserve’s bee problems. Disappointingly, when I reported these observations to Perky Pet and suggested that the company consider at least offering red replacement flowers, the representative’s only comment was, “Well, our customers like the yellow flowers.” Not their feathered customers, of course, but the ones with the cash.

But some people report no problems with bees on feeders with yellow parts, and others have terrible bee problems on all-red feeders. Why are some feeders with yellow parts ignored by bees? And why do some red feeders attract bees while others don’t?

The story is actually pretty complicated and starts with the different ways that bees, birds, and humans see the world. According to “Why Are So Many Bird Flowers Red?” by Miguel A. Rodríguez-Gironés and Luis Santamaría, the eyes of most bees, including honeybees, contain three types of color-detecting cone cells (trichromacy), each of which is sensitive to different wavelengths of light in a different band. The three sensitivity peaks fall at 340 nm (near-ultraviolet), 430 nm (violet-indigo), and 540 nm (yellow-green). Human eyes also contain three types of cone cells, but the peak sensitivities fall around 424 nm (indigo-violet), 530 nm (yellow-green), and 560 nm (yellow). Birds go us and bees one better with four types of cones (tetrachromacy) peaking at 370 nm (near-UV), 445 nm (indigo), 508 nm (green), and 565 nm (yellow) (Goldsmith 2006). The graphic below is my attempt to visualize the differences in color sensitivity between humans, honeybees, and hummingbirds:

Notice that none of these photoreceptors peaks in the red range (~650 nm), yet we humans (and most birds) see red reasonably well. That’s because each type of cone cell can be stimulated by wavelengths near as well as at its peak. The sensitivity declines with increasing distance from the peak wavelength, so it takes some pretty intense red light to stimulate the yellow receptors of birds and humans.

So, leaving out some evolutionary bells and whistles that may enhance avian and insect color vision, bees’ eyes are substantially less sensitive toward the red end of the spectrum than our eyes or birds’ eyes. Both Rodríguez-Gironés & Santamaría and Spaethe, Tautz, and Chittka (2001) note that bumblebees presented with red flowers have a harder time locating them. Logically it should be likewise with red vs. yellow feeder parts, but it’s not quite as simple as that.

One variable has to do with the bees’ ability to see ultraviolet light. Insect-pollinated flowers often reflect UV differently from surrounding foliage and may even have UV markings that help attract and guide their pollinators. Hummingbirds can see into the near ultraviolet, too (Goldsmith 1980), yet their flowers don’t seem to use UV cues. In a tropical study, Doug Altshuler (2003) found that hummingbird-pollinated flowers reflected light mainly in the visible red wavelengths. Altshuler concluded that:

…hummingbird-pollinated flowers are not tuned specifically to hummingbird color sensitivity but instead may decrease conspicuousness to bees and other insects that have poor visual sensitivity to long-wavelength [e.g. red] color.” [emphasis mine]

Applying this conclusion to feeders, it’s clear that differences in UV reflectance between different types of plastic could make some feeders, or feeder parts, as conspicuous to bees as a neon sign in a dark alley, regardless of how they appear to human eyes.

But it turns out that contrast is more important than color alone in helping bees find flowers. The compound eyes of insects are capable of very low image resolution. The view through even the best compound eye was compared by a 19th-century naturalist to “a picture about as good as if executed in rather coarse wool-work and viewed at a distance of a foot” (Land 1997). In modern terms, think about viewing a normal (low-def) TV screen or CRT computer monitor from about an inch away.

Spaethe and colleagues noted that bees see color less well than contrast. The further a bee is from a flower, the larger that flower needs to be for it to be able to discriminate its color. It also takes them longer to process differences in color than differences in contrast. Naturally, the most important contrast is between flowers and the surrounding green foliage, so when searching for flowers at distances of more than a few inches, bees tend to home in on objects that stimulate their yellow-green receptors significantly more or less than the background foliage. The green receptors in bees’ eyes can be stimulated by red light of sufficient intensity, but whether they perceive the difference between a red flower and its green background depends in part on the relative intensities of light reflected from each.

Color and contrast notwithstanding, a combination of opportunity and necessity may be responsible for much of the variation in bee problems at hummingbird feeders. Not only do drought, late freezes, and other factors that reduce flower availability tend to increase bee problems, but some bees may have evolved to take advantage of bird-pollinated flowers as a back-up or even primary nectar source. Raine and Chittka (2005) note that among bumblebees, the one species that showed a distinct (though secondary) preference for red is Bombus occidentalis, a species whose range in western North America is rich in hummingbird-pollinated flowers. The marauding carpenter bees (Xylocopa californica arizonensis) that rob nectar from my cultivated salvias also take advantage of the natural bounty of bright red, tubular ocotillo flowers in the late spring dry season (Scott et al. 1993). Like a naturally abundant hummingbird flower, hummingbird feeders present a rich resource for any bee capable of taking advantage of it. A poorly designed feeder is going to be more profitable for bees to exploit than a thoughtfully designed one, which is why a feeder’s vulnerability to bee problems may go beyond color.

Until we know how different hummingbird feeders appear to bees and other insects, we can’t be absolutely sure how much influence color alone has on the potential to attract unwelcome feeder visitors. Nevertheless, the scientific evidence clearly indicates that it’s wise to avoid feeders with parts that reflect light in the yellow to violet “bee-friendly” portions of the visible spectrum.

References:

Altshuler, Douglas L. 2003: Flower color, hummingbird pollination, and habitat irradiance in four neotropical forests. Biotropica 35(3):344–355. Abstract

Goldsmith, Timothy H. 2006. What Birds See. Scientific American. PDF

Goldsmith, T.H. 1980. Hummingbirds see near ultraviolet light. Science 207:786-788.

Land, Michael F. 1997. Visual acuity in insects. Annual Review of Entomology 42:147-177  PDF

Raine, Nigel E. and Lars Chittka. 2005. Colour preferences in relation to the foraging performance and fitness of the bumblebee Bombus terrestris. Uludag Bee Journal, Volume 5, Issue 4 (November 2005): pp. 145-150. PDF

Rodríguez-Gironés, Miguel A., and Luis Santamaría. 2004. Why Are So Many Bird Flowers Red? PLoS Biol. 2004 October; 2(10): e350. Link

Scott, P. E., S. L. Buchmann, and M. K. O’Rourke. 1993. Evidence for mutualism between a flower-piercing carpenter bee and ocotillo: use of pollen and nectar by nesting bees. Ecological Entomology 18:234-240.

Spaethe, J., J. Tautz, and L. Chittka. 2001. Visual constraints in foraging bumblebees: Flower size and color affect search time and flight behavior. PNAS 98(7):3898-3903. PDF

Thorp, R. W., and M. D. Shepherd. 2005. Profile: Subgenus Bombus. In Shepherd, M. D., D. M. Vaughan, and S. H. Black (Eds). Red List of Pollinator Insects of North America. CD-ROM Version 1 (May 2005). Portland, OR: The Xerces Society for Invertebrate Conservation. Link