What do Hummingbirds Eat?

Introduction

What do hummingbirds eat? This is a question often asked of hummingbird lovers. It's a simple question, and you'd think the answer would be simple too. But hummingbirds are an enigma. They are one of the most studied bird families, but every time we think we know everything about their habits, they do something that contradicts that knowledge. What they eat is a good example.

When early naturalists saw hummingbirds flitting from flower to flower, they assumed that the birds were feeding on liquid nectar from the flowers, just like bees. They thought that was all the birds ate.

This reasoning, however, had its critics. Some argued that hummingbirds did not visit flowers for nectar, but rather for the tiny insects hidden in the flowers. This view was supported by numerous sightings of birds swatting midges and other small insects from the air.

In addition, aviculturists who tried to raise hummingbirds in captivity found that the birds did not live long on a diet of only sweets; in fact, hummingbirds that had access to protein sources did well in captivity. It has been suggested that the reason they drank sugary liquids was that confined birds were likely to consume foods that they would not naturally eat in the wild.

All of these conditions led to the theory that the majority of the birds' food was invertebrates. Any nectar ingested was therefore only a consequence of the birds eating flowers.

The logic of the insect alone

In order to determine what exactly hummingbirds were eating, early ornithologists shot a number of them - a perfectly legal activity at the time - to examine their stomach contents. After dissection, they discovered remains of prey such as flies, midges, wasps, aphids, beetles, leafhoppers, and spiders, whose abdominal cavity was often completely filled. Zoologist and museum director Frederic A. Lucas found that the stomach of one hummingbird contained the remains of as many as 50 individuals, probably more.

What he and other scientists did not find, however, was nectar. As a result, small invertebrates seemed to be the answer to the question of what the birds' diet was. For these researchers, the case was closed.

However, there were flaws in this reasoning based solely on insects. First, the stomachs of some of the hummingbirds were empty, even though the birds had been seen eating shortly before they died. What ornithologists at the time did not realize is that nectar and other liquids are digested quickly and are therefore almost impossible to detect in the stomach. This is especially true for hummingbirds because their stomachs have an unusual structure. As hummingbird expert Walter Scheithauer describes it, the outlet is not at the bottom as in other birds, but above, directly next to the stomach entrance. The nectar can flow directly into the intestine without passing through the stomach.

The formal proof that sugary fluids - and thus nectar - are an essential part of hummingbird diets came when people began placing containers filled with sugar water outside. Although they have access to all the insects they can eat, the birds still voraciously drink the liquid from hummingbird feeders.

Artificial feeders also proved that hummingbirds were not limited to eating invertebrates and nectar, as honey or sugar mixed with water were both used to replace nectar. (Today, most experts consider ordinary white table sugar to be the best nectar substitute for birds, and discourage the use of honey or other sweeteners in hummingbird solutions.)

Of course, nectar, honey, sugar, and insects are not the only things hummingbirds consume. Some hummingbird stomachs have also been found to contain pollen grains. The stomachs of two blue-throated hummingbirds examined by biologists Clarence Cottam and Phoebe Knappen contained 10% and 15% pollen. It is not known if this food is ingested intentionally or if it is simply a consequence of nectar consumption.

Tree sap

It is known, however, that most hummingbirds also drink tree sap. Accounts of hummingbirds drinking tree sap date back to at least the 1880s. It turns out that tree sap is an ideal alternative to nectar. Like nectar, the sap is generally composed of sucrose, water and amino acids in relatively equal proportions. For this reason, hummingbirds have developed close associations with sapsuckers. Ruby-throated hummingbirds and rufous hummingbirds are believed to synchronize their spring migration northward with that of sapsuckers. In Canada and the northern United States, these hummingbirds arrive at their nesting sites several weeks before the flowers bloom. Hummingbirds are able to acquire all the energy they need from the sap produced by the efforts of the sapsuckers.

This affiliation with sapsuckers continues throughout the rest of the year as well. Rufous, ruby-throated, broad-tailed, and calliope hummingbirds have been found nesting near the sap wells of the sapsuckers, and some hummingbirds follow their meal tickets from the drill site to learn the location of each. Hummingbirds have even been observed defending the trees where the sapsuckers feed on other birds.

Sap wells also provide hummingbirds migrating in the fall with much-needed refueling stations, where the birds can spend up to a week before continuing south. Even during the winter, hummingbirds depend on the sap wells of sapsuckers to provide much-needed food.

One of the hummingbirds' favorite saps is sugar maple sap, the same substance used to make maple syrup. Several researchers have offered maple syrup - the boiled sap, not the artificial product - to hummingbirds over the years to observe the birds' reaction, with positive results. The results are positive. The birds readily accept the sweet drink.

Fruit juice

Hummingbirds are also known to sip the juice of overripe or previously pecked fruit. One might think that they would only prey on insects attracted to the fruit, but early evidence shows that this is not the case. In an 1894 article in The Auk, Janet L. Hine writes of observations made on a rubythroat, saying, In our neighbor's orchard a hummingbird sucked the juice out of an apple while a girl was peeling it.

This is not the only record of hummingbirds eating the juice of apples and other fruits. Several species of hummingbirds find the sweet liquid of persimmons appetizing; Anna's hummingbirds seem particularly fond of the juice, and many observations have been made of these fruits. Pears, oranges, and prickly pears are other fruits whose juice may attract hummingbirds. Drinking the juice from these fruits has been observed often enough that it is no longer considered an unusual occurrence.

The sweet emissions of trees and insects

Hummingbirds, however, have a few more tasty surprises in store for us. In August 1981, in Colorado Springs, Colorado, researchers Peter Kevan, Sherrane St. Helens, and Irene Baker noticed several broad-tailed, rufous hummingbirds hovering under the tips of some Gambol oak branches, licking a substance that was leaking from them. The source of the discharge turned out to be a number of lesions caused by bacteria on the twigs. Upon examination, biologists found that the secretion from the wounds was similar to the nectar of the flowers the bird's visit - a high ratio (1.117) of sucrose, glucose, and fructose - but had a higher concentration of amino acids than flower nectar.

This effluvium is not a conventional food source for hummers, as it normally evaporates quickly and hardens when exposed to sunlight. In this particular case, however, it had rained the evening before, and the weather was still wet and cloudy that morning, allowing the substance to remain in a liquefied form that the hummingbirds could easily consume.

Since hummingbirds have a sugar-centric lifestyle, it makes sense that they would be attracted to a sweet substance secreted from tree wounds, and it stands to reason that they would also be attracted to the sweet excretions of insects. In fact, a number of such observations have been made. On several occasions, birds have been seen ingesting honeydew exuded from filaments protruding from the bark of trees, which, upon close examination, were found to be from scale insects. Each filament produced a small drop of clear, sweet liquid at its tip, which the hummingbirds eagerly devoured. Of course, mealybugs are not the only insects that produce honeydew: aphids also produce honeydew, and there is at least one report of hummingbirds eating the sugary emission of these insects. Given the sweetness of the secretions emanating from these insects and the lesions on the trees, it is not difficult to understand why hummingbirds would add them to their diet. However, this is not the case for everything they eat. Some of the substances they consume do not seem to be part of their normal diet.

Sand, ash, and seawater

On many occasions, different species of hummingbirds have been seen dipping their beaks into substances such as sand, wood ash, and seawater. Those who witnessed these events were certain that the birds were not eating insects, but ingesting the object itself. Why do snorers do this? All of these unusual foods tend to be high in calcium and may also contain sodium and other minerals. Since the majority of the birds observed were female - at least in the cases where the sex of the hummingbird was mentioned - it has been proposed that the reason for this activity is to replace calcium and other minerals lost during egg production.

Ashes, sand, seawater, insect secretions, pollen, and fluids from fruits and other plant parts are a far cry from the nectar and insects once thought to be the only sources of nutrition for hummingbirds. There are undoubtedly other foods that birds eat, foods that will once again change our idea of what hummingbirds eat.

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What do Hummingbirds Eat?