To continue my series on rainforest ecology, let’s take a look at the birds that live in this fascinating area.
Neotropical birds were evolved from dinosaurs from possibly up to 125 million years ago, having both inherited reptile features and feathers. From there, different birds, for example the chaffinches and the bramblings, were separated, and ended up with very different adaptations over time.
Most birds have hollow bones with criss-cross struts. They have no teeth or jaw muscles, but rather a gizzard in their stomachs which grind up their food.
In contrast to mammals, which all have 7 vertebrae, birds have a larger range of motion in their necks because they have 11-20 vertebrae.
Their feet and beaks are adapted to their lifestyle, and can be used for swimming, walking, perching, seizing prey, climbing, filtering, probing, tearing meat, drilling holes, and/or eating insects or seeds, depending on which bird discussed. For example, the blackbird is adapted for eating worms and berries, while the blue tit is better suited for eating insects. Chaffinches are adapted for eating seeds, while the short-tied eagle is conditioned for eating meat.
Courtship and Mating
For courtship and mating, birds of a feather may come together at set times of the year, when they show off their fitness for breeding. Like humans, birds also need to bond in order to make a relationship last and make rearing successful. Some ways of accomplishing this are:
- Mutual displays (for example, ‘fencing’ gannets both engage in a ritual of using their beaks to ‘fence’)
- Chase and display
- A call to show that they are fit to breed
- The lek refers to a male communal display area, where they pose as mannequins to impress females.
Breeding happens briefly but frequently, and can take place in the air. Birds can be monogamous, which means that they only have one pairing for life, or promiscuous, which means that a male mates with many females. A reversal role refers to when a male will take care of the young instead of a female.
Nests are helpful in identifying the species of bird that occupies it, as many nests are distinctive to the species. Sometimes a bird may have no nest, preferring to tunnel into sand or find shelter in a tree hole. They may also use plasterwork or create floating nests (drifts on water) to roost.
Bird eggs can be classified by shape, pattern, and color, and exhibit adaptations depending on the species of bird as well.
For example, cliff bird eggs have a small top and larger bottom so that when they roll, they go in circles and therefore do not fall off the cliff. Game birds and owls have spherical eggs to maximize the surface area to volume ratio. Some aerial birds hatch long eggs which fit their streamlined bodies.
Other birds hatch eggs camouflaged to their surroundings or with shapes that allow for a neat arrangement in their nests.
Most chicks develop an egg-tooth while incubating, which they can use to chip their way out of the shell and lose afterwards.
DDT and other chemicals introduced by humans create a deficiency of shell hardness, causing the eggs to break prematurely and endanger bird populations.
In this section I will mainly be talking about how birds may vary in appearance. Commonly a species may exhibit sexual dimorphism, which is when the male and female have different plumages, such as the mallard duck. Often, a juvenile bird may appear different than it will as an adult as well, such as a gull. Birds may also take on different appearances depending on the season (i.e. summer and winter), for example the snow bunting, or when it comes time for molting. There may be subspecies of a bird which can exhibit a wide variety of characteristics, such as the wheatear. A common oddity (what an oxymoron, I know) which may cause a member of the same species to vary in plumage is albinism, for example the partially albino blackbird. Again, based on its surroundings, some species have adapted their plumage to suit their habitat through camouflage, such as the bittern.
Now is also a perfect time to mention the Handicap Principle. Perhaps the best way to explain this is through an example such as the male peacock. The flashy, resplendently feathered individuals in a species appear to be more attractive to the opposite gender, however this impedes their survival. Hence, the biologically fitter individual signals their greater fitness through a handicapping behavior or morphology which effectively lowers this quality. Pretty ironic, eh?
Songs and Calls
Birdsong almost deserves a post on its own, because they are so fascinating. There have been entire compositions of music inspired by birdsongs, and often I remember that we exist not merely for survival when I hear them.
They sing for pleasure, true, like us, but birdsong also has a multitude of other uses as well, such as identification, creating a screaming display, calling out to locate others, keeping together, as defense, to attract a mate, to establish territory and make warnings, or to make hunger calls. Commonly when we wake up early we witness birds coming together to form a “dawn chorus”.
Birds don’t have a voice box or larynx like we do, but a syrinx to make noise. A syrinx is a series of membranes that stretch and relax as air passes over.
One birdcall that I remember is that of the slate-colored solitaire, which sounds exactly like the jingling of a bunch of keys.
An extremely captivating type of bird, the lyer, is able to imitate virtually any type of sound. For example, if it hears a logger’s saw in the woods, it will be able to reproduce that sound exactly. Freakish!
The ability to fly is a defining, but not necessary characteristic of birds (think penguins and emus!) Apart from a means of daily commute, flight makes migration much easier for the birds that do so, and their wing and tail shape depends on their needs for survival. For example, the starling bird is starkly different from the peregrine (falcon).
- Pointed wings allow for fast flight.
- Short and rounded wings allow for a quick take-off but a relatively short flight.
- Long, broadly shaped wings allow a bird to sustain a longer flight.
- Long, forked wings allow for better steering in fast flight.
- Stiff flight feathers give a bird leverage for tree climbing.
In a group, birds may also use a noisy flight pattern to confuse and defend themselves from a predator. This behavior is known as mobbing.
Why do many birds migrate? We have all seen it. Due to the changing of the seasons, food sources can become scarce, and the winters lead to a harsher climate, which birds want to avoid.
Migrating is also an instinctive behavior, and birds can either do this separately or with a group. They seem to find their way naturally through an internal compass. If we break it down we will find that they use the sun and the stars, a magnetic sense, physical waypoints on the ground, and the observation of polarized light to guide their way.
Say you catch a bird in your mist net or you observe one on a point count. What do you write down in your log to take back to camp to identify later? Most of these defining features can be useful: habitat, behavior, flight, size, shape, song, bills, legs, plumage, and nest.
- Ground birds reproduce slowly and are heavily hunted. This is bad!! Some examples are the chacalacas, the curassows, and guans (cracidae).
- Flashy birds such as the trogon and motmot are a perfect demonstration of the Handicap Principle.
- Ramphastidae include the toucans, aracans, and coucanets. These are fruit eaters and have hollow beaks.
- Trochilidae include the hummingbirds, which exhibit controlled aerobatic flight, using a figure 8 beating of their wings. They have an extremely fast metabolism, feed on nectar, and are good for the flora because of pollination. An interesting theing they do is they go into a torpid state which allows them to use 95% less energy at a lower body temperature while resting.
- Vultures, or cathartidae, are specialist feeders. You probably know what they are. Sometimes they take their prey live.
- The red-capped manakin moonwalks!
Birds as an Indication of Forest Health
It is common knowledge that our planet is in a state of decline and that many species of the animal kingdom are being lost every day. Birds can be used to indicate how healthy a forest is because they are diverse, well studied, abundant, apparent, predictable in their response to disturbances, and closely associated to other species. They are relatively easy to census, because of their bright colors and highly vocal habits.
Therefore, ornithologists are really important in conservation efforts! Long live the birds and the bird aficionados.
Thank you for reading! I hope you learned something new, and feel free to do more research concerning this subject and let me know about it in the comments below!