HUMMINGBIRDS: ¿INSECTS OR BIRDS?

Trochilidae family, known as hummingbirds, is endemic of the New World. For some authors they belong to the Apodiformes order, together with the swifts, while for some other authors hummingbirds constitute their own order, Trochiliformes. Despite theses academic discussions the most remarkable about hummingbirds is both their morphology, with some unique adaptations within the birds class, as well as their key ecologic role on their ecosystems, as we shall see later the Green-fired Firecrown.

Some hummingbirds are among the smallest birds in the world, some species barely reaching 6 cm. All them stand out by their colorful plumage, with green, blue, red and orange tones with metallic sparkles that change depending on the sunlight angle. Their wing beat is extremely fast, with frequencies up to 80 flaps per second, so sometimes they may be taken for insects. Moreover, their wing design is unique among birds, allowing them not only for a static fly over the same point in space, but also to fly backwards. Their bill in long and thin, sometimes slightly curved. These two adaptations, their flight technique and the bill are directly related to the way they feed: similarly to insects they introduce the bill on the corolla of flowers; then, slightly opening the bill, they sip the nectar with their long tongue.

Hummingbirds flying technique has a huge energetic expenditure, so they have to consume 5 times their body weight in food every day. In order to achieve this they need to feed every few minutes, resting the rest of the time to save energy. Their thighs and toes are very weak, as they are adapted to perch on branches, but they can not walk nor run on the ground. Logically, they live on areas with abundance of flowers, like honeysuckles, and as well as insects they fulfill an important role on the pollination of these plants. Like bees, the pollen grains that get stuck to their bellies pass from one plant to another, dispersing the pollen and therefore allowing the plants reproduction. Also as bees, they are able to calculate the amount of sugar on every flower, letting behind the ones with insufficient sugar. The nectar contains a lot of energy, but is poor or proteins, vitamins and minerals, so they supplement their diet with insects and spiders, specially to feed their chicks.

As well as some insects, hummingbirds have coevolved together with some types of plants, that therefore received the name of ornithofilus. Some hummingbirds feature bill adaptations based on the shape of a very limited number of flowers. The plants, in turn, develop red, orange and pink tones to attract hummingbirds and do not develop waves on the ultraviolet spectrum, to avoid attracting insects.

GREEN-BACKED FIRECROWN

The Green-backed Firecrown (Sephanoides sephanoides), is the southernmost species of the hummingbirds family and the only one living out of tropical regions. They live on the cold Andean-Patagonian forests, from South Mendoza to Tierra del Fuego, being the only nectarivore bird on theses forests. They are then strangers, representatives of the tropical birds in this cold and mountainous world. That might be the reason why for the Mapuche culture hummingbirds are related with trips across supernatural worlds. The male has a bright red crown, sometimes turning into orange or even yellow, as you can see on the pictures. The female lacks this colored crown, so it is easy to distinguish them. They nest on humid and dark spots, always near the ground. Both parents build a tiny nest, using moss and lichen fibers, hanging them from bush branches.

During winter part of the population migrate northwest, aiming for more temperate areas. The ones who stay on the Andean forest, when temperature drops down -5º and the food is scarce, have the ability to enter an hibernation-like, deep sleep state known as torpor, needed to preserve energy reserves from failing to a critical level. During this state both body temperature and heart rate fall dramatically, returning to normal levels when the conditions are favorable again. In towns a lot of people puts dispenser on their courtyards, where they put a sugary solution mixed with some pollen, so hummingbirds can found some easy food, especially during the winter months, helping to conserve this lovely species.

A THREE-WAY PARTNERSHIP

Green-backed Firecrown has also an amazing biological relationship with two of its neighbors of the Patagonian forests: one is the quintral (Tryxterix corymbosus), a parasit plant that grows over trees like lenga, ñire and coihue. The other one is the monito de monte (little monkey of the mountain, Dromiciops giroides), a small marsupial mammal of the same family as opossums and weasels, who is endemic of this forest. He is nocturnal, spending most of his time on the tree branches, as he has opposing thumbs and prehensile tail, like some primates. That is the reason of the name “little monkey” although he has nothing to do with primates.

The quintral is one of the few vegetal species in Patagonia that flowers during winter, bringing some color to the snowy forests. Therefore, its flowers are a fundamental source of energy for some species in winter. The Green-backed Firecrown is one of them, so they can survive the harsh winter by feeding from quintral flowers.

But the quintral need also some allies, in this case not for feeding but for reproduction. One of them is the hummingbird, who by eating on the quintral flowers allows for the pollination. Then, the quintral produces berries containing the seeds, which fall into the ground. But seeds are not able to germinate as they fall into the ground. First, they have to pass by the digestive system of some animal, but not anyone. The germination chances are maximum only when the seeds pass by the digestive tract of the monito de monte. The diet of the monito is quite varied, but in spring the quintral berries are on of its main food sources. Inside theses berries are the seeds, that are then dispersed by the monito de monte when it defecates on the branches of trees and bushes.

And here you have the full interaction between these three: the monito de monte fosters the dispersion of the quintral, allowing him to conquer new territories. This in turn benefits the Green-backed Firecrown, who has new areas with food available in winter. The hummingbird return the favor by pollinating the quintral flowers, and the monito the monte, who feeds from the quintral berries, rewards him by dispersing the seeds. Here we see how deep and complex are the relations between the different living beings in one ecosystem. By knowing about these kind of interactions we can take conscience of the chain damage that we can produce when just one species disappear from an ecosystem that has been working in perfect balance for thousands of years. The same damage can be done when exotic species are introduced. A good example is the expansion of the American Mink on the Andean Patagonia, which is badly harming some aquatic birds. Buy we will discuss that some other time.

REFERENCES:

Narosky, Tito e Yzurieta Darío, Birds of Argentina & Uruguay, Vazquez Mazzini Editores, Buenos Aires, 2010.

Díminich Cecilia, Compadres del Sur, Revista Fundación de Historia Natural Félix de Azara, Número 1 - Año 2013.

Proyecto Freebirds Guía de Aves.