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NESTING BEHAVIOR OF HUMMINGBIRDS

by Jon Freidman

Size and materials The nests of hummingbirds are some of the natural world's daintiest structures. Often they are about half the size of an English walnut, cleverly camouflaged, and hard to spot. All species of hummers line their nests with the softest down from seeds, fibers from hairy leaves, soft bird feathers, and/or whatever is generally available from any particular location.

The most important material Almost invariably, a hummingbird nest is bound together and lashed to a support with liberal amounts of spider webbing. Spider silk, the material that spiders produce from their bodies to create their webs, is one of the most amazing materials. It is thinner in gage than even the finest human hair, stronger than steel in relation to its thickness, somewhat sticky, and a very elastic material. Hummingbirds use it to create the nest itself and to anchor the nest to the branch or object to which the nest is affixed. The thinness of the spider silk allows the hummer to easily manipulate it when wrapping the outside and/or inside of the nest. The natural strength of the spider silk insures that the nest is strong enough to endure the rigorous nesting process. Some nests are so well built that they outlast the first year's use by several years. If the nest hasn't suffered from age and weather deterioration, it may be used again. Sometimes a new nest is built inside an older nest that has survived time and weather, provided it is still firmly anchored. As spider silk is elastic in nature, the nest expands as the babies grow larger.

Camouflage The outside of the nest is decorated with small bits of lichen, moss, bark, flowers, peeling paint chips from old buildings, feathers, or whatever the bird finds that coordinates with adjacent foliage to blend the nest into the surrounding environment. I've found hummingbird nests camouflaged with tiny yellow flowers while a Palo Verde tree was in bloom. I was amazed to discover it, as I had passed by this nest several times a day and never before noticed it. Sometimes the rim of the downy cup is curved inward to help prevent the loss of the eggs in high winds. 

Black-chinned hummingbird nest in Tucson's Foothills
Note the spider silk anchoring the nest to the branch
Photo by Douglas Everett

Placement While the construction of nests is similar from species to species, the placement of the nests varies widely. We've seen or heard (oftentimes from customers) of nests built in unusual places. And while the exact placement of nests does vary, the hummers usually locate their nests in places that offer protection from wind, sun and rain. They build them in places where predators cannot easily spot them from above. We know of several unusual locations hummers have used to their advantage. The handle of a security screen door on a customer's house became the site of a hummer nest and prevented the family from using that door until the babies fledged. Another nest was discovered inside the pocket of a men's dress shirt that was left hanging on a clothesline for an extended weekend. Hummers have built nests atop a single hanging light bulb in a garage, on a door knocker, and even on the antennae of a car parked in one place for an extended time.

Height above ground The most frequently used nest site is in a tree or shrub, but the height varies along with the species of bird and plant. Black-chinned hummingbirds choose small overhanging limbs in vines, herbs or trees, 4 to 8 feet above a small stream or dry wash. The Lucifer hummingbird nests four to six feet up in an agave. Magnificent hummingbirds utilize horizontal limbs of deciduous trees from 10 to 50 above ground level. Blue-throats favor pine-oak woodlands with nesting sites in herbs and trees from 1 to 30 feet high. Costa's nests are typically found in yuccas from 3 to 5 feet high.

Unusual locations South American Hermit hummingbirds attach their nest to a living leaf that acts as a protective roof. To accomplish such an engineering marvel, the female hovers to wrap a scrap of webbing on the leaf tip. Then she uses fragments of vegetation to construct a shelf that projects out from the inner side of the leaf tip. She rests on the shelf while finishing her cone-shaped nest to hold her eggs. Dangling from under the nest is a "tail" of shriveled leaves, fibers and other vegetation.

The Sooty-capped Hermit of Venezuela suspends its nest from a single "rope" of spider web underneath bridges, culverts, and inside dark buildings. Since the "rope" is attached to the open cup nest at only one point, the nest would tip precariously if she did not counterbalance the nest by using spider silk "cement" to attach small mud pellets or little pebbles which dangle below the nest. Similarly, the Andean Hillstar uses regurgitated nectar or saliva to glue its large, well-insulated nest to well-protected and inaccessible locations in the high Andes. It increases the amount of material on one side of the nest to balance it. The Chimborazo Hillstars live in Ecuador up around 13,000 to 15,000 feet. They are just below the ice cap of the volcano Cotopaxi where hail, high winds, snow, and freezing night time temperatures occur regularly. To keep their young warm enough, they nest in caves or deep ravines in relatively close proximity to each other. (Five nests were found within a seven foot radius.) Although some of these locations seem precarious, they probably do protect the nests from rain and most terrestrial predators.

Nest construction Only female hummingbirds build nests. Like many other birds, they employ their beaks, feet, and breasts in constructing the nest. The female uses her bill to gather and transport materials, to poke them down into her nest, to smooth the outside of the nest, and to press the wall toward her breast which she uses to shape and round the nest as she rotates in all directions. She bounces up and down which suggests that she is using her feet to tamp down and compact the materials in the bottom of the nest.

Building time The time it takes to build a nest varies from species to species. The work has been completed in as little as two to three days. More often it takes a week, but may take as much as 2 to 3 weeks. Often the female lays eggs in a partially completed nest, and then finishes it as she incubates the eggs.

Size of eggs Hummingbirds almost always lay two tiny, elongated white eggs. If more than two eggs are found, they were probably laid by two females. In North America, the smallest eggs are those of the Calliope Hummingbird, measuring about 1/2" by 1/3". The smallest eggs of all hummers belong to the tiny Bee Hummingbird of Cuba and several other neighboring islands. The largest eggs are those of the South American Giant Hummingbird, at 3/4" by 1/2".

Black-chinned hummingbird nest in Tucson's Foothills
Note the spider silk anchoring the nest to the branch
Photo by Douglas Everett

Incubation of eggs In many cases, the female begins to incubate her eggs as soon as the first one is laid. Usually the eggs are laid in the morning, about 48 hours apart. However, this can vary from 24 to 72 hours. The eggs hatch in approximately the same time sequence as they were laid. If they do happen to hatch at the same time, this means that incubation did not start until the second egg was laid.

The female, who incubates the eggs alone, leaves the nest frequently during the day to feed and/or gather new reinforcing materials for her nest. The time each species sits on the eggs in the daytime ranges from less than a minute to three hours per sitting. Absences last from less than a minute up to half an hour. The number of times the nest is left varies from 10 to 110 per day. Even with the most frequent absences, the hummer's eggs are kept covered from 60% to 80% of the daylight hours. These foraging trips may contribute to the relatively long incubation period for such small eggs. In general, the minimal incubation period is from 14 to 17 days, but may be prolonged by inclement weather or harsh nesting conditions. The Andean Hillstar takes 20 to 23 days to incubate its eggs.

Feeding baby chicks Newly hatched chicks are almost naked, blind and totally helpless. They seem to be all head, with tightly closed eyes and the barest indication of a beak. Even so, their crops are well developed and the mother begins feeding them extraordinary amounts of food shortly after hatching. Newborns are fed a diet almost entirely of insects and gradually nectar is introduced. Mom feeds her babies by inserting her long beak well down their throats and regurgitating the food from her crop into that of the young ones. The babies' crops protrude like large goiters from the right side of their necks. Mom almost always divides the food equally. Feeding happens from 1.2 to 3 times an hour.

Temperature tolerance The youngsters are born with only two rows of tiny down feathers along the center of their back. They lack a distinct downy stage, and their contour feathers burst out directly from pinfeathers. But despite the lack of downy insulation, they are amazingly tolerant of temperature fluctuations. The mother broods them at frequent intervals for only the first 8 to 12 days. Then she leaves them exposed at night. By this time, they have developed enough temperature regulation to stay many degrees warmer than the night air in their snug downy nest. Some species nesting in the high mountains (such as the Calliope, Blue-throat, and Magnificent in Southern Arizona) may continue to cover their nestlings until 18 days have passed.

Nest hygiene Unlike some other birds, hummingbirds always have clean nests. The eggshells are removed or crushed on the bottom of the nest after hatching. When the nestlings are very young, the mother carries away, swallows or flips the droppings out of the nest. When older, the young rise up and expel their own droppings over the edge of the nest.

Nest expansion and fledging Growing chicks become crowded in such a small nest, but as the chicks grow, the nest expands to keep them warm and fit their bigger bodies. This phenomenon is enabled due to the use of that extraordinarily strong, somewhat sticky, and elastic material hummers so much depend upon - spider silk. The two growing birds push up past the top edge of the nest as their thermoregulatory mechanism matures. Sometimes they split the nest apart and either fall to the ground or remain on the flattened nest. When about 16 days old, the young are well-feathered and begin to beat their wings furiously while hanging on to the nest to avoid being lifted off.

Wrong assumptions It is extremely important to not interfere with nature if you are unsure how to interpret what you may be seeing. Humans have a tendency to want to "rescue" baby birds that have left or fallen out of the nest. True nestlings may need some human intervention to get them back into the nest but fledglings should be left alone unless clearly injured. Humans also feel that they can adopt abandoned babies. Baby birds are never abandoned by the parent, but parent birds will not attend to the babies if humans are present and too close.

Fledging When the young are ready to leave their nest, they do it on their volition, without any urging from their parents. Few hummingbirds leave the nest before they are three weeks old. Nesting periods of 20 to 25 days are not uncommon. Inclement weather or harsh environmental conditions may prolong the date of fledging. Andean Hillstars from high in the mountains fledge after 30 to 40 days. From their first attempt, hummers are excellent flyers, often covering 50 feet in their first flight.

Feeding babies Our Black-chinned Hummingbird feeds her young for at least two weeks after fledging. A Scaly-breasted Hummingbird was fed until it reached 65 days old. Juveniles do not follow the mother around to forage, but do have a particular place where the mother comes to feed them. If the youngsters are not in place when she arrives, she may call to them. Most of what is written about hummingbird nesting puts the majority of the work of raising the young on the female. But every now and then, male assistance has been observed. In Venezuela, photographs were taken by Ernst Schaefer of a pair of Sparkling Violet-ears incubating their eggs in turn. For the next 16 days, this male who could be identified by his abnormally light crown, helped feed the one baby that hatched. Closer to home in California, Mrs. Dale Clyde saw a male Anna's repeatedly feed a nestling whose mother had disappeared.

Broods Two broods per season are the norm for most hummingbirds. Sometimes the same nest is used again if it is not too worn, eroded or weathered. At other times, a new nest is built on tip of the first one. Anna's, Black-chinned and Rubythroat Hummingbirds have been noted to build a new nest and even begin incubating their second clutch of eggs while still feeding nestlings in the first nest. As this article was nearing completion, one of our customers called and reported an observation of this very behavior!

More to learn Next time you are in the store check-out our research library at the store. Dan True is perhaps the best hummingbird nesting behavior expert in the country and you can read about nesting in his book, Hummingbirds of North America which we have is the store. He also guest authored two articles about hummingbird nesting in the July/August and the Sept/October, 2001 issues of our newsletter. We have archival copies you can read in non-lending research library. So, pull up a comfy chair, learn, and enjoy!


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