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Science & NatureGreen TalkBirds and their role in the web of life

Birds and their role in the web of life

By Theresa Peluso

Just about everyone likes birds.
(All photos: Brent Eades)

What wild creature is more accessible to our eyes and ears, as close to us and everyone in the world, as universal as a bird? David Attenborough 

I realized that if I had to choose, I would rather have birds than airplanes. Charles Lindbergh 

Birds are fascinating creatures, an integral part of our lives and our legends. In China, the crane was considered a symbol of immortality. The Dravidians of India considered the peacock to be Mother Earth. In South Africa, Hamerkop nests were protected for fear that people who didn’t, would be struck by lightning, and in Mexico, the Aztecs considered the eagle a symbol of the sun.  In European mythology, doves were thought to be the souls of the departed, owls were imbued with wisdom and ravens were a sign of misfortune.  And that’s just a small sample of the intricate role birds have played in different cultures and traditions.  (For more information, see .)

This enchantment with birds has endured.  In recent times birdwatching has become a huge industry, with an estimated 50 million people in the United States alone, spending roughly $41 billion per year on this activity.  More than 20 million Americans take birding-specific trips every year.

Birds, which are members of the class Aves, live and breed in most terrestrial habitats and on all seven continents. Several bird species have adapted to life on and in the world’s oceans. Colombia has the most bird species, with 1,826, followed by Peru with 1,804 bird species, and Brazil, with 1,753 species of birds.  In Ontario, as of April 2017, 495 bird species were recorded, of which 291 are known to breed in this province.  Within Lanark County, the Mississippi Valley Field Naturalists Birding Committee have recorded 283 different species observed by local birders in recent years.

As we all know, birds are warm-blooded vertebrates that lay hard-shelled eggs, and are characterized by feathers, beaks, wings (except for the extinct moa and elephant birds), a high metabolic rate, a four-chambered heart, and a lightweight skeleton.  Most winged birds have the ability to fly. The wings of some birds, like the penguin, have evolved for use in swimming.

The earliest ancestor of all birds is considered to be the Archaeopteryx, which dates back to 150 million years ago, and lived in today’s southern Germany. This bird-like dinosaur was the size of a jay, with toothed jaws, a long lizard-like tail, and flight feathers. The closest living relatives of birds are the crocodilians.  According to cladistics (cladistics is an an approach to biological classification in which organisms are categorized in groups based on the most recent common ancestor), birds are considered to be dinosaurs, and the only surviving ones.  For more information, see

By 50 million years ago, most of the bird orders we know today had established themselves.  During the next 20 million years, songbirds (of the passerine order) evolved, and proceeded to diversify.  And 200,000 years ago, when the first human-like creatures appeared, most modern bird species were in existence. The descendants of the Archaeopteryx now range in size from the 5-cm bee hummingbird to the 2.75-m ostrich.  More than half of the approximately 10,000 living species of birds are passerines.

Calculated in Gigatons of carbon (Gt C), the biomass of wild birds is .002 Gt C, compared with plants (450 Gt C), humans (.06 Gt C) and fish (.7 Gt C).   Interesting fact:  the carbon biomass of chickens is .0154 Gigatons, which is almost 8 times the biomass of wild birds.

A study of the Wikipedia entry on Birds ( provides many interesting facts, but I have noted here some of the more fascinating ones.

Birds have an incredibly complex and efficient respiratory system.  When they breathe in fresh air, 75 percent of it bypasses the lungs and flows directly into a posterior air sac attached to the lungs, which connects with air spaces in the bones and fills them with air.  The other 25 percent of the air goes directly into the lungs.  When the bird exhales, the used air is expelled from the lungs and replaced with the fresh air stored in the posterior air sac.  This enables the bird’s lungs to receive a constant supply of fresh air. Birds also have a highly efficient system for diffusing oxygen into the blood.  The surface-area gas-exchange volume is 10 times greater in birds than mammals.  As a result, birds have more blood in their capillaries per unit volume of lung than a mammal.

Another adaptation to flight is evident in the digestive systems of birds.  Their intestinal size is reduced, but this is compensated for by the enhanced ability of their intestines to absorb the nutrients in the food that passes through.

Some birds, such as parrots and members of the crow family, are among the most intelligent of animals.  Several bird species make and use tools, and pass on their knowledge to their progeny.  Birds are very social, and often cooperate in breeding, hunting, flocking and attacking predators.  Many of them are renowned for their plumage, bird songs, and dances, which they use to communicate with other birds.

Humans have, since time immemorial, admired the incredible colourful plumage of birds; but there’s a whole other dimension of this plumage that we don’t see because, unlike birds, we can’t perceive wavelengths in the ultraviolet range.  In effect birds can identify ultraviolet colours in the plumage of other birds that we can’t.  Would we see crows and ravens differently if we were gifted with ultraviolet vision?

The diet of birds depends on the species, and even for a given species, on the time of year or on whatever food is available to them.  Because birds have no teeth, their digestive system is adapted to process food items that are swallowed whole.  Bird diets can include nectar, fruit, seeds, grasses, aquatic plants, carrion, small birds and mammals, insects, spiders, fish, shellfish, and worms.

We are also well aware of the fact that many bird species inhabiting regions with wide seasonal variations in weather – like Eastern Ontario – , migrate to optimize the availability of food and of places to breed.  The trigger for this major undertaking is the length of daylight, as well as weather conditions.  Before migrating, birds fatten themselves up and reduce the size of some of their organs.  Landbirds have a flight range of around 2,500 km; shorebirds can fly up to 4,000 km, with the exception of the bar-tailed godwit, which can fly up to 10,200 km non-stop!  Seabirds are the all-time champions when it comes to long migrations, with sooty shearwaters making an annual round trip of 64,000 km.

Most migrating birds seem to have a well-defined flyway.  Scientists have hypothesized that these birds seem to have an internal GPS that enables them to follow the same route every year, created as young birds imprint on the sun and stars to help orient themselves, and possibly also as they learn to recognize landmarks.  The individual organs of birds also contribute to this remarkable ability.  Their eyes interact with their brains in a region called “cluster N” which probably helps birds to determine which way is north.  In addition, the inner ear of birds contains tiny amounts of iron in the neurons, which reinforces this sense of direction.  And apparently, their beaks also play a part in enabling them to identify their exact position because of the trigeminal nerve connecting the beak to the brain.  This trigeminal nerve also, it is hypothesized, helps birds to evaluate the strength of the Earth’s magnetic field, and hence their location relative to the poles.  In addition, some researchers think that birds can smell their way across a flyway, creating an “olfactory map” of the terrain as they pass over it.  (For more information on bird migration, see and

Most birds form flocks, whether continually or just at certain times, such as when migrating.  Although the benefits of flocking, mainly increased protection from predators and increased foraging efficiency, may be offset by the greater risk of food scarcity, and by bullying of socially subordinate birds.  Sometimes birds of different feathers do flock together, and sometimes birds will form associations with non-avian species, especially if it increases their access to food or provides them with protection from enemies.

So the fascination with birds lies not just with their beautiful plumage and their melodious calls, but also with their physiological complexity, feats of endurance and athletic talents.  But do birds have an important role to play in the web of life?

While some birds are adaptable (like pigeons and crows), and can adapt to changes in the environment, others are highly specialized in their habitat or food requirements.  Even within a single habitat, like a forest, certain species will feed in the forest canopy, others beneath the canopy, and others on the forest floor.  Some birds may eat only insects, or only fruit, or only nectar.  The same goes for birds that live in grasslands, the desert, wetlands, tundra and on or near the ocean.

Some birds that feed on plants are important pollinators and seed dispersers, and some may have a mutually exclusive relationship with a particular plant – they feed solely on that plant, and are the only means for that plant to propagate itself.  In other cases, the excrement of birds is an important source of soil enrichment for certain habitats.

Many bird species, such as purple martins, nuthatches, woodpeckers, bluebirds and swallows, play an important role in controlling insect populations, including disease-carrying and agricultural pests.  Collectively, insectivorous birds eat between 400 and 500 million tonnes of arthropods annually.  That puts them on an equal footing with arachnids, whales and humans, in terms of the amount of animal protein consumed per year.

Carrion birds like vultures, and sometimes eagles, crows and ravens, help to get rid of dead and rotting carcasses.  Other birds, like woodpeckers, create tree cavities for other animals to use, such as other birds, porcupines, and mice.  Birds in turn, provide a source of food to larger birds, foxes, weasels, snakes and skunks.

Now that we’ve been reminded about how amazing and important birds are, what about their endangered status?

An assessment of all the world’s bird species was completed in 2016 under the auspices of the International Union for Conservation of Nature and Natural Resources (IUCN), by the Bird Life Partnership.  This assessment reported many significant findings.

Of the roughly 10,300 extant species that were fully assessed, about 1,430 are threatened (more than 14 percent of the total), 145 to 163 are extinct or extinct in the wild, and approximately 8,800 are not threatened at present.

Of the 291 breeding birds in Ontario, 36 are at risk.  Apart from the Greater Prairie-Chicken and Eskimo Curlew, which are now classed as extirpated, 12 are endangered (at risk of extinction), 10 are threatened (on their way to being endangered), and the rest are of special concern.  See this link for more information: .

Although human activities in the past enabled a few species, such as the chimney swift and the barn swallow, to thrive, they have caused many other species to decline or become extinct.  The fact is that human activity has resulted in bird extinctions as far back as 12,000 years ago.  Research and modelling indicate that human colonization of the Pacific islands prior to 10,000 BCE caused the global extinction of more than 1,000 species of birds.  At least some of these losses may be attributed to animals like rats and cats accompanying these humans.

Roughly 25 bird species have been identified as becoming extinct between 10,000 BCE and 1500 CE.  An additional 12 bird species are believed to have become extinct from 1500 to 1900 CE.  One classic example is the passenger pigeon in North America.  In 1810 just one of many masses of these pigeons flying over the Indiana Territory was estimated by Alexander Wilson, the father of scientific ornithology in America, to consist of over 2 billion birds. Wilson’s rival, John James Audubon, watched a flock pass overhead for three days and estimated that at times more than 300 million pigeons flew by him each hour.  One hundred years later, there were no passenger pigeons anywhere to be found.

During the 20th century, extinctions escalated, to nearly 500 species having gone extinct.  And the rate of extinction has increased dramatically less than two decades into this century, to about 150 birds now extinct, and a further 1,430 birds threatened with extinction (as per the above-referenced 2016 Bird Life Partnership assessment).

Why are birds declining in species and numbers, despite their remarkable abilities?  Some researchers blame acid rain, associated with the loss of calcium in the environment, which could affect birds’ eggs.  This acid rain, which contains high levels of nitric and sulfuric acids, is mainly caused by human activities, such as coal-burning power plants, factories and automobiles.  Winds may spread these acidic compounds through the atmosphere over hundreds of kilometres. Acid rain (or snow or fog) also contaminates our water and soil when it comes in contact with the ground.

The increased unpredictability of the food supply of birds is yet another factor. Because of climate change, the life cycles of the insects on which many birds count, especially after a long, arduous flight, are no longer synchronized with the migration cycles of these birds.  Insects are now hatching and maturing much sooner, leaving nothing for the birds to feed on, especially those birds unable to adapt to the new circumstances.  One study found that the diet of chimney swifts, over a period of about 40 years, had changed from protein-rich (true) bugs and beetles to less nutritious flies, which may be one reason for the decline in their numbers.  Then, of course, there’s the fact that these birds, which successfully adapted to living in chimneys, found that their old haunts were replaced by new-fangled capped chimneys with metal flues.

Ever since Rachel Carson’s book Silent Spring was published in 1962, we have done almost nothing in response to her documentation of how DDT was accumulating up the food chains from the insects it was designed to kill to the creatures that ate them.  Even though DDT was eventually banned around the world (except in malaria-prone countries), it is still showing up in the same quantities in bird tissues, suggesting that exposure has not declined significantly in the past 40 years.  (See .)

To make things worse, every year more and more chemical formulations of pesticides are being designed that, despite all promises to the contrary, end up being proven to incapacitate and kill non-targeted species, including birds, and humans too. One research paper published in 2001 by Canadian Wildlife Service toxicologist Glen Fox ( reported the following:

…research-based studies of bald eagles, herring gulls, night herons, tree swallows, snapping turtles, mink, and beluga over the past 30 years have revealed a broad spectrum of health effects in the Great Lakes-St. Lawrence basin including thyroid and other endocrine disorders, metabolic diseases, altered immune function, reproductive impairment, developmental toxicity, genotoxicity, and cancer…. In all cases, a strong argument can be made for an environmental etiology, and in many cases for the involvement of persistent organic pollutants, particularly polychlorinated biphenyls, polychlorinated dibenzo-(italic)p(/italic)-dioxins, and polycyclic aromatic hydrocarbons. (end of quote)

It should be clear that with humans at the top of the food chain, we are NOT exempt from this contamination, and that the other, newer pesticides are just as toxic, but haven’t been around long enough for this to be proven beyond doubt.

So these avian creatures, capable of living in icy regions and in tropical heat, in parched deserts and on stormy oceans, on airless mountaintops and in earthen burrows; capable of flying non-stop for days on end – they are dying off because of human behavior.

Climate change and pollution are just two of the many threats.  The most commonly cited human threat to birds is habitat loss, but there are even more:  overhunting, collisions with buildings or vehicles, fishing bycatch, and competition and predation from non-native invasive species.  Plastic pollution is yet another threat, killing up to 1 million sea birds ever year.

A 2013 Environment Canada study showed that, despite various government regulations protecting birds, more than 270 million wild birds are killed in Canada each year because of human-related activity. (See for more information.)

Here are the chilling statistics (note the number of birds killed per year in Canada in parentheses):

  • Domestic and feral cats (200 million)
  • Power lines, collisions and electrocutions (25 million)
  • Collision with houses or buildings (25 million)
  • Vehicle collisions (14 million)
  • Game bird hunting (5 million)
  • Agricultural pesticides (2.7 million)
  • Agricultural mowing (2.2 million)
  • Commercial forestry (1.4 million nests, equivalent to 900,000 adult birds)
  • Communications towers (220,000)

How can we help to stop this annual slaughter of these creatures?

Support organizations like Ontario Nature, founded in 1931, which protects wildlife and wild spaces in Ontario with its three core programs: habitat and species conservation (nearly 3,000 ha of protected land), conservation education and public engagement.  This charity, with a Nature Network of 150 conservation groups, also advocates for environmental law and policy changes to increase the level of land and wildlife protection in Ontario.

How can we stop this slaughter?

  • Prevent bird collisions with your windows by putting up curtains or window decals.
  • Protect birds from pets by keeping your cat indoors and your dog from straying.
  • Clean your bird feeders (dirty feeders can spread disease).
  • Don’t buy illegally-caged birds.
  • Prevent the proliferation of plastic trash by using cloth grocery bags, eschewing non-reusable bottles and packaging, and recycling whatever you can.
  • Restore natural habitat in your community by planting trees and shrubs in public places.
  • Keep your distance (this includes pets) and leave fledglings where you find them. If you think a bird is really orphaned, contact the Ottawa Valley Wild Bird Care Centre  ( for instructions.
  • Slow down when driving to give yourself more time to respond if an animal crosses your path (also a great idea to prevent deer collisions).
  • Buy bird-friendly products, and avoid those grown by companies that have deforested natural areas to grow and process their products.
  • Grow native plants in your garden to provide food, nest sites and cover for birds. There is a program geared to eligible farms registered under the Canada-Ontario Environmental Farm Plan to encourage greater protection and conservation of habitat for species at risk. For more information, visit .
  • Start a club, or get involved in a club that promotes bird appreciation and works to protect them. The Mississippi Valley Field Naturalists ( abounds with bird enthusiasts who would love nothing better than to share their wealth of knowledge with you, and have you help them with their bird protection programs. Their Environmental Education Program for children is also great, and so are the Mississippi Valley Conservation Authority’s summer programs ( for children.
  • Get outdoors and enjoy nature, and learn about the birds in your community, and what makes them thrive. Better yet, invite a friend, or your children and grandchildren, to join you.  (Being outdoors in nature also has proven benefits for your own personal health and well-being!)
  • Support conservation by joining the Mississippi Madawaska Land Trust (, Ontario Nature (, and Environmental Defence ( Become a citizen scientist by joining one of Ontario Nature’s bird-data collection projects.  Bird Studies Canada ( is another group that works to advance the understanding, appreciation and conservation of wild birds and their habitat in Ontario and elsewhere.
  • Reduce your carbon footprint by minimizing carbon-fuel-motorized travel and recreation, and reducing energy loss in your house.
  • Eliminate the use of non-environmental pesticides both on your property and in your community. Even if these poisons don’t kill birds immediately, they kill them eventually by damaging the birds’ habitat and food sources, and accumulating in their systems.
  • Learn the hunting laws and make sure they are observed. Report illegal activity related to plants and wildlife to 1-877-TIPSMNR (8477667).
  • Protect shoreline habitat by leaving it undisturbed, and advocating for regulations to restrict motorboat activity. Boat wakes, especially from water-ski and wakeboard boats, churn up the water and damage the river or lake bed, destroy bird nests, and boat propellers kill chicks.  At the very least, restrict these vessels only to very deep water on major waterways.

The damage already done is huge, and the task to repair it is also huge, but we must do everything we can to change this ongoing destruction of nature and the birds that dwell among us.

I leave you now, with two more quotes:

One way to open your eyes is to ask yourself, “What if I had never seen this before? What if I knew I would never see it again?” Rachel Carson

The question is whether any civilization can wage relentless war on life without destroying itself, and without losing the right to be called civilized.  Rachel Carson






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