Bird Physiology and Migration

By in Migration, Physiology

The fall bird migration is a protracted spectacle extends well into November or beyond.  The presence of numbers of sandpipers and plovers on the mudflats and the scarcity of Tree Swallows and Barn Swallows tells us that the fall migration is already well underway.

In contemplating migration, I continue to be amazed by the ability of birds to fly such long distances.  Sure, bats and insects can fly but none can hold a candle to birds when it comes to feats of flying.

We all know about many of the features of birds that allow them to master the air: hollow bones, light yet strong feathers for producing lift and thrust, and streamlined bodies.  However, other adaptations for flight are subtler and perhaps unexpected.  The various organ systems for birds all contribute to make a bird a consummate flying machine.

Let’s start with the urinary or excretory system. The function of any excretory system is to rid the body of nitrogen-containing wastes from the breakdown of proteins.  The most common waste product is ammonia, a toxic material.

For fish and invertebrates that live in freshwater or the sea, it’s pretty easy to get rid of the ammonia by producing a large quantity of dilute urine.  Water is not a problem for an aquatic organism.

Humans and other mammals can’t use this same mechanism.  We would have to essentially spend our lives drinking water and urinating to flush the toxic ammonia from our bodies.

To solve this problem, we convert ammonia to a substance called urea.  Urea is toxic only in very high concentrations and can be dissolved in water.  So, the problem is solved for mammals.  By converting ammonia to urea, our kidneys can concentrate the urea and get rid of it with a moderate amount of water.

This method of removal of nitrogen waste does not work for birds.  Many of the avian adaptations for flight involve making the body as light as possible.  If birds produced urea, they would have to carry around an unacceptably heavy load of water to flush the urea from their body.

Instead, birds convert their ammonia wastes to a compound called uric acid.  It takes more energy to convert ammonia to uric acid than to urea.  However, the cost is worth it for birds because uric acid is non-toxic and also does not dissolve in water.

Birds therefore get rid of their nitrogen waste by using only enough water to push the paste-like uric acid down the excretory system.  The white center in bird guano is uric acid.

Let’s consider the digestive system.  Living birds do not have teeth.  Rather the grinding of food is accomplished by the gizzard, the second of two stomachs of a bird.  How can this arrangement contribute to flight?

First of all, teeth are heavy.  Particularly for long-distance migrants, a few tenths of a gram can make all the difference.  Secondly, teeth would make it difficult for a bird to keep its head in the proper position during flight.  A bird’s head needs to maintain a particular position to be aerodynamically efficient.

By having its “teeth” in its gizzard, a bird can lower its center of gravity.  The position and weight of the gizzard enable the bird to maintain an efficient posture during flight.

The demands of flight can be seen in the reproductive system.  During the reproductive season, the male reproductive organs or testes are quite large.  However, once the breeding season is over and migration begins, the gonads of the males shrink to less than 1% of their breeding season weight.  That is some weight savings!  The difference between the weight of the gonads of House Sparrows between the breeding and non-breeding season is 500 times.

Most female birds have only a single ovary.  Exceptions are most hawks and some pigeons and gulls that have a pair of ovaries.  The ovary swells during the breeding season and then regresses dramatically during the non-breeding season to reduce the weight of a flying bird.

Finally, we can consider one aspect of the skeleton in birds: the shape of the sternum or breastbone.  In flying birds, the ventral side of the sternum has a large sail or carina.  This carina serves as the attachment point for the two muscles that raise and lower each wing during flight.  Most of the power generated during flight occurs during the downstroke and this muscle is the larger one.

The breastbone of ostriches and other non-flying birds is flat like our breastbones, strongly suggesting the carina is a structure that evolved to facilitate flight.

[Originally published on August 21, 2011]

Crossbills

By in Species Accounts

Have you noticed how heavy the cone crops are this summer on red spruce, balsam fir and larch?  Cone abundance varies greatly from year to year for all these species but this year’s crop stands out as truly exceptional.

These cones matter greatly to the suite of northern finches that irrupt (come into) Maine in search of conifer seeds.  These species include Pine Siskins, Evening Grosbeaks and crossbills.  These nomadic birds wander broadly in search of abundant food.   Although the abundant cones on our conifers do not guarantee these irruptive finches will grace us with their presence this winter, the abundance of food should keep any irruptive birds happy for the winter.

We have two crossbills in North America and both can be found in Maine.  These species are the Red Crossbill and the White-winged Crossbill.  Usually, the White-winged Crossbill is the more common species.

The hallmark of the crossbills is the peculiar overlapping arrangement of the upper and lower bill. One bill crosses over the other.  Sometimes the upper bill curves to the left and other times to the right.  Why such an odd bill?

Crossbills are specialists on the seeds of conifers.  Take a look at any conifer cone.  The cone has a number of scales.  At the base of each scale, the seeds of the conifer can be found.  Most birds have a difficult time negotiating the scales to get to the seeds deep within the cone.

Not crossbills however.  A crossbill inserts its bill between two scales of a cone.  The crossed points of the bill act as a wedge, increasing the distance between the two scales.  The strong tongue of the crossbill can then be inserted to the base of the scale and the nutritious seeds removed and eaten.

The crossbills must be quite agile to position themselves in the proper position on the cone to extract seeds.  Crossbill feet are quite strong.  The behavior of crossbills while feeding reminds many people of parrots whose feet have great dexterity.

Although the crossed bill serves these birds marvelously in feeding on cones, the specialization comes at a cost.  Crossbills are quite awkward in handling food that other finches readily eat such as thistle or birch seeds.

Usually crossbills feed on cones that their bills can handle with greatest efficiency.  The Red Crossbill has a larger and longer bill than the White-winged Crossbill.  Red Crossbills feed on white pine, balsam fir and sometimes hemlock cones.  White-winged Crossbills feed on smaller cones like those of larch and red spruce.

Depending on conifer seeds is risky.  Cone production by these trees is notoriously variable.  In some years, hardly any cones are produced.  In other years, every tree of a given conifer species seems loaded with cones.  During the years of high cone production, the crossbills do well.  In years of poor cone production, crossbills must wander until they find an area where the conifers are having a good cone year.

Crossbills are therefore nomads, wandering over wide areas to find abundant cones, the one food for which they are supremely adapted to use.  The ceaseless wanderings of the crossbills means their abundance will be highly variable at a particular location.

Crossbills don’t have a particular nesting schedule.  When the birds find a large cone crop, they may initiate nesting regardless of the time of year.  Red Crossbills appear to require day lengths of at least 12 hours before they will nest.  However, White-winged Crossbills have been found nesting in every month of the year.

Red Crossbills have been the focus of recent study by ornithologists interested in bird classification.  These workers have noted that the call notes of Red Crossbills vary from place to place throughout North America.  Differences were found in bill size and body size that correlated with different call notes.  Evidence now indicates that there may be at least eight different species of Red Crossbills.  Telling them apart in the field is very hard and must be done in most cases by identification of the distinctive calls.

Three types of Red Crossbills have been found in Maine and a fourth eastern type occurs in Newfoundland.  These forms have not been officially recognized as distinct species by the American Ornithologists Union but it is only a matter of time.  Identifying the crossbills in the field will become a real challenge.

If you are interested in learning more about the vocalizations and morphology of the different types of the Red Crossbills, here is a great web site: http://research.amnh.org/ornithology/crossbills/

You can even hear sound files of the different crossbill types.

[Originally published on August 7, 2011]

Bird Reproduction and Energy Budgets

By in Reproduction

Many of the birds that nest in Maine are feeding nestlings now.  Some have already fledged young.  This time of year is a good occasion to consider the striking variation in the reproductive biology of birds.

Ornithologists use the term life history to describe reproductive traits of a bird species.  Aspects of the life history include number of eggs per nest, number of nesting attempts per year, age at first reproduction and life expectancy.  To understand some of the variation in life histories of birds, we can start with a discussion of a household budget.

Warren Buffett and other extremely wealthy people don’t have to bother with keeping a budget for their families but most of us do.  The first budget items we have to pay each month are our necessities: mortgage or rent payment, groceries, heat, electricity, transportation.  Let’s call these budget items maintenance.

If we have money left over at the end of the month, we can invest that money.  We may choose to save for retirement, for a bigger house, for education, for a birding trip to Antarctica.

Birds, like all living things, have an energy budget to manage.  Every bird has a limited amount of food it can find and eat and therefore its energy budget is limited.  A bird must spend much of its energy budget on maintenance.  In this case, maintenance means the costs of staying alive (basic metabolic needs).  Any remaining energy is then available for investment.  The investment for birds is a genetic investment.  By raising young, the parents get their genes represented in future generations.

A person just joining the workforce is likely to have a starting salary lower than she can expect later in life, leaving little to invest in the future.  Some birds follow the same pattern.  Albatrosses may not reproduce until they are ten years old.  Presumably, these oceanic wanderers become proficient over time at finding their patchy prey.  These birds only reproduce after their energy budget becomes larger.

A local example of delayed reproduction is the Bald Eagle, reproducing only in the fourth or fifth year of life.

Some people are willing to be mobile to make more money at the beginning of their careers.  White-winged Crossbills provide an avian parallel.  These birds depend on conifer seeds for their energy.  Conifers produce huge bumper crops of seeds every few years.  The crossbills move throughout the northern portions of the northern hemisphere to find areas where the local conifers are heavy with cones.  With large amount of energy available, the crossbills immediately start nesting.  In fact, White-winged Crossbills have been reported nesting in very month of the year!  I remember seeing White-winged Crossbills on nests in northeastern Vermont one year in January with the temperature 30 degrees below.

A high salary is not the sole consideration for employment.  Some people find great satisfaction in their job even though the salary is modest.  Let’s travel to the tropical oceans. These oceans are usually nutrient poor and have low fish abundance.  Fish-eating tropical birds like the Sooty Tern have little energy to invest in reproduction.  They produce a single egg per nesting attempt.  Compare that to the typical clutch size of three eggs for temperate species like the Common Tern.

If you have some money to invest, where do you put it?  Some cautious investors will invest in treasury bills, certificates of deposit or a savings account.  Investors willing to take a risk may choose to invest in several speculative stocks.

In birds, egg size determines the amount of risk.  Some birds, like American Woodcocks, lay fairly large eggs for their size.  These eggs contain large amounts of yolk that provides nutrition for the developing embryo.  When the chick hatches, it is feathered and capable of sight.  The chick can start looking for food soon after it breaks free from its shell.  This sort of development is termed precocial.

On the other hand, songbirds take a riskier approach.  The egg of a Red-eyed Vireo or Gray Catbird is relatively small and has only a modest amount of yolk.  When the young hatch, they are blind and unfeathered.  They are utterly dependent on the parents for warmth and food.  This development type is called altricial.  Altricial birds typically are not capable of finding their own food until at least 11 days after hatching.

Precocial development, in which the mother makes a high investment in each egg, usually results in some offspring surviving.  Altricial development is riskier because the parents must gamble on finding sufficient food after the chicks hatch to complete development.

[First published on July 24, 2011]

Egg Color

By in Reproduction

Bird eggs vary widely in shape, size and color.  Often, the species can be identified using characteristics of an egg.

Egg coloration remains a topic of great interest in the ornithological community.  The eggs of many birds are speckled with dark colors against a white background.  It’s not heard to understand the function of such coloration.  The speckling of the eggs breaks up the outline of the egg. Such camouflaged eggs seem to disappear within a nest or in a scrape.

We believe that the ancestral condition for egg color in bird was immaculate white.  Even now, species that nest in cavities where eggs are not visible are not camouflaged.

However, camouflage may not be the sole explanation for speckling in eggs.  We know that the protoporphyrin pigment that makes up the speckling strengthens the eggshell.  The strengthening effect may be particularly important where birds have trouble acquiring calcium in their diets.

But how then can we explain the blue-green eggs of an American Robin?  Robins lay their eggs in open nests.  Such eggs would hardly seem to be camouflaged.

As it turns out, many other thrushes, including bluebirds, produce blue-green eggs.  Blue-green eggs are also laid by birds in many other families.  So, the question of why some eggs are blue-green has some widespread application within the avian world.

There is no shortage of speculation on the reasons for blue-green eggs.  These hypotheses include warning coloration (the eggs must be distasteful), advantages in absorbing heat and cryptic coloration.  Unfortunately, support of these explanations is weak or lacking.

A recent hypothesis with some experimental support is the sexual-signaling hypothesis.  The blue-green color in the eggshell comes form a substance called biliverdin, which has antioxidant properties in the mother.  A healthier, more vigorous mother can produce more biliverdin for her eggs.  Her male partner can judge the condition of his mate, and of his soon-to-be offspring, by the depth of the blue-green color.  The male will then respond to this signal by bringing more food to the young once they hatch.

Recent work by Daniel Hanley and colleagues with Gray Catbirds showed that females with higher antioxidant capacity produced deeper blue-green eggs.  They also showed that the amount of food provided by male catbirds was directly related to the richness of the egg color.

[First published on July 10, 2011]

Nest Architecture

By in Book Reviews, Reproduction, Uncategorized

Humans are unusual among mammals in that we build our houses. Sometimes we use natural materials and other times plastic or other artificial materials that do not occur in nature. Beavers are the only other local mammals I can think of that build substantial houses.

Most birds however are excellent builders, manifested usually in the form of a nest. Some nests are extraordinarily intricate while others are massive.

The excellent skills of birds in building nests are remarkable in at least three ways. First, most of the building is accomplished with the aid of only the bill. The feet may help in holding material and the body itself can be used to mold the shape of the nest but the majority of the work is done with the bill.

Second, birds don’t get a lot of practice. Most birds build a single nest per season and some use the same nest for years.

Lastly, the instructions on how to build a nest appear to be genetically encoded. Birds know how to build a nest although in some species older, more experienced birds seem to build with more skill than first-timers.

The source of most of the information in today’s column comes from a recent book by Peter Goodfellow entitled Avian Architecture: How Birds Design, Engineer & Build. The book is richly illustrated with over 300 color images (photographs and drawings). The text is limited but adequate. The drawings and text allow the author to give the reader a firm understanding of how various nests are made.

The coverage goes from simple nests to more complex, sometimes communal nests. Goodfellow breaks nests into twelve categories and devotes a chapter to each type. The author provides several examples of each type of nest. Examples are drawn from birds around the world.

The simplest nests are called scrape nests. They are built by simply gouging a shallow depression in the ground. Sometimes eggs are laid directly on the ground and in other species, a lining is created in the scrape. Female Common Eiders pluck feathers from their breast to line their simple nest.

The depth of the scrape is critical. For Pectoral Sandpipers nesting on the arctic tundra, the scrape depth minimizes heat loss. Shallow scrapes expose the eggs to wind chill and deep scrapes cause the eggs to lose heat to the permafrost below.

Nesting on the ground is risky so it is no surprise that a scrape nest and the eggs laid within it are camouflaged. The young usually show precocial development so they can leave the nest soon after hatching.

A number of birds nest in holes and tunnels. Some, like woodpeckers, make their own holes and some, like kingfishers, make their own tunnels in riverbanks. Other species are secondary cavity nesters, using either natural or existing holes or tunnels. Such birds may elaborate the holes by adding linings of plant material. A good local example is the House Wren. The Great Hornbill of southeastern Asia provides a remarkable example. The female adds mud to the opening of her nest cavity, essentially sealing herself in with only a slot opening to the outside. She and her young once they hatch are dependent on the male for all their food. The mother may remain cooped up in her nest for two months. The narrow opening to the nest prevents predators like martens from entering.

Aquatic nests are made by only four types of birds: jacanas, marsh terns, grebes and rails. Aquatic nests are immune from attacks by terrestrial predators.

The architecture of an aquatic nest usually includes aquatic plant materials that float dues to airspaces within, thus keeping the eggs above water. Some aquatic nests are fixed to the shoreline while others float in deeper water.

Cup-shaped nests are the most common type of nest. A strong cup with a lining provides protection for the eggs and chicks. The nest is anchored strongly, usually with spiders’ silk. Most cup-shaped nests are located above the ground.

The Ruby-throated Hummingbird attaches gray lichens to the outer wall of its nest. The nest looks like the broken base of a branch of the tree on which it sits.

Domed nests combine characteristics of cup-shaped nest and cavity nests. The entrance hole is an important architectural consideration, minimizing predator risk and the chilling effect of the dominant winds.

The book covers so much more: mound incubators that use the heat of composting material, platform nesters, colonial nesters and others. The text is easy to understand and can be shared with children. This book provides a great entry to the wonder of birds.

[First published on June 26, 2011]

Birds, Rice and Weddings

By in Physiology, Uncategorized

It’s time for a little myth-busting today.  Now that the wedding season is upon us, one often hears the dire warning that throwing rice on the happy couple poses a risk for birds. Rice supposedly swells with water in the gut of birds, causing the birds to die.  Let’s consider the digestive system of a bird to see how ridiculous this claim is.

The digestive system of birds varies from species to species according to diet but the basic components of the gut are the same.  Food is first taken into the mouth cavity.  Since birds have no teeth, the food is not broken into smaller pieces as we do with our teeth.  However, seed-eating birds do have well-developed salivary glands that secrete enzymes into the oral cavity.  These enzymes begin the breakdown of the hard coat that surrounds seeds.

The food next passes through the esophagus.  In some cases, the esophagus has a large sac, the crop, where seeds or other food may be stored before it can be processed in the lower part of the gut.  A crop can be advantageous because a bird can take in a large quantity of seeds and then seek shelter, digesting the stored food away from predators.  The esophagus and the crop do not produce enzymes and play no active role in digestion.  The esophagus serves as a connector to get food from the oral cavity to the first of two stomachs in a bird.

The first stomach is called the glandular stomach or proventriculus.  This organ is similar in function to our own stomachs.  The liquid in the stomach contains concentrated hydrochloric acid as well as proteases, enzymes that break down proteins.  The nutritious part of a seed, the endosperm, is rich in proteins.

Next the food passes into the muscular stomach or gizzard.  The gizzard is the site of mechanical digestion; it is where a bird chews its food.  The inner portion of the gizzard has a thick, hard lining of folds and ridges. The muscles surrounding the lining move the ridges and folds past each other, grinding the food.  Many birds, including seed-eaters, retain grit in the gizzard to help to break the food down into smaller and smaller pieces.

How effective is the gizzard of a seed-eating bird?  We know of some experiments with turkeys.  Turkeys are able to pulverize English walnuts, steel needles and surgical lancets in their gizzards!  It is ludicrous to imagine that rice kernels would pose any threat to a seed-eating bird.

The scientific name of the Bobolink is Dolichonyx oryzivoru; the species name means rice-eater.  A common name for these birds in the southern states is rice birds.

So feel free to shower the happy couple with rice as they depart for their honeymoon.  By the way, I have heard similar advice about the dangers of feeding bread to birds, which seems even more absurd.

In the last column, I wrote about the potential importance of birds in spreading Lyme disease ticks and the Lyme disease bacteria.  A paper published in 1992 in the Wilson Bulletin described the use of guineafowl (the Helmeted Guineafowl is the formal name of these gray and white birds) as a “folk” defense against Lyme disease ticks on Shelter Island, New York as well as Nantucket and Martha’s Vineyard in Massachusetts.

In Africa, Helmeted Guineafowl eat a variety of arthropods and glean ticks from warthogs.  The practice of using guineafowls in Nantucket was impelled by the discovery of three ticks in the gut of a guineafowl.

The authors of this article, David Duffy, Randy Downer (now a neighbor of mine in China) and Christie Brinkley, described experiments done in two towns on Long Island.  The study involved setting up wire cages to keep guineafowl out of portions of lawns adjacent to wooded areas.

The authors found more Lyme disease ticks in the cages, showing that guineafowl can reduce the abundance of these ticks.  The guineafowl had significant impacts on other species of arthropods as well.

The results of this study suggest that guineafowl can be part of a management system to reduce the likelihood of Lyme disease, reducing the need for acaricides (tick poisons).

I bring up this interesting study in today’s column because of the claim that ticks can pass through the guts of birds unharmed.  Ticks do have a hard exoskeleton but I can find no scientific data in support of the assertion.   I think a tick would fare no better than a steel needle in passing through a large seed-eater’s gut.  So until I see convincing results, color me skeptical on this claim.

[Column originally published on June 12, 2011]

Recent Ornithological Literature

By in Recent Ornithological Literature

In this post, I will provide a synopsis of several scientific papers that recently appeared in scientific journals.  All of the papers deal with birds that occur regularly in Maine and most of the research was performed in our state.

Michael Schummer, Brad Allen and Giuming Wang recently published a paper in the Northeastern Naturalist where they analyze changes in reproductive success of Maine waterfowl.  They used brood survey data collected between 1955 and 2007.  The authors analyzed six species: Mallard, American Black Duck, Wood Duck, Common Goldeneye, Ring-necked Duck, Hooded Merganser.

Brood sizes declined for all species except Mallards and Hooded Mergansers over the survey period.  For those four species, clutch size declined between 0.9 ducklings per brood to 1.7 ducklings/brood.

The authors do not know the reasons for the declines but the results should arouse concern.  The four species are quite different in nesting behavior and in diet suggesting that a general loss of habitat quality may be to blame.

Bald Eagles are adaptable predators that sometimes kill live prey and at other times scavenge.  The diet of Bald Eagles varies seasonally and geographically but commonly includes invertebrates, fish, reptiles, birds and mammals.

Medium-sized mammals in their diets include rabbits, sea otters, arctic foxes and raccoons.  Eagles can kill any of these mammals.  We do have evidence that Bald Eagles will feed on hoofed mammals (deer, elk, caribou and domesticated cattle and sheep.  For these larger mammals, biologists presumed they were scavenged by the Bald Eagles.

A recent study by Jared Duquette and colleagues published in the Northeastern Naturalist provides evidence that a Bald Eagle killed a white-tailed deer fawn and flew it to its nest for its two eaglets.  The fawn had been radio-collared.  It weighed six pounds.  Thanks to the radiocollar, the workers could locate the carcass (including two legs and most of the hide) to the eagle’s nest.

In an article in the Wilson Journal of Ornithology, Mason Cline and Joanna Hatt describe the potential of lobster traps in causing deaths of landbirds.  The two authors participated on the Bath-Brunswick Christmas Bird Count in January 2010.  At Merepoint Neck in Brunswick, they noticed 80 metal lobster traps stored above the tideline.  Three live Blue Jays were in three of the traps.  Furthermore, the Blue Jays were ripping the flesh from nine other Blue Jays that had perished within the traps.  The jays were apparently enticed to enter the traps to feed on the baitfish remnants inside and then could not exit.  This observation established idle lobster traps as potentially lethal traps and demonstrated cannibalism for the first time in Blue Jays.

More than three million lobster trap tags have been issued to the Maine lobster industry.  The number of traps is certainly higher than that with all the spare or unused traps not in current use.  The authors rightly point out that if only a fraction of those traps are stored after the lobster season in such a way that birds can enter, the traps represent a potentially significant source of mortality.  Fortunately, storage of the traps to obscure the openings and removal of the baitfish can reduce the threat.

In the journal Frontiers in Ecology and the Environment, Jory Brinkerhoff and three co-authors explore the impact of birds in increasing the risk of Lyme disease.  The black-legged tick is the primary vector of the Lyme disease bacterium (Borellia burgdorferi).  Borellia parasitizes a wide variety of vertebrate species, including at least 71 species of North American birds.

The black-legged ticks in their early (larval) stages are mostly found on white-footed mice.  The immature (nymphs) occur on a variety of birds, mammals and even reptiles.  The adult ticks are primarily dependent on white-tailed deer.   However, the blood of white-tailed deer causes the Borellia bacteria to die.  So, deer can certainly disperse black-legged ticks but not the Lyme disease bacterium.

Anytime, an infected black-legged tick bites a host it can transfer Borellia to the host or, if the host is infected, the tick may become infected.  It’s a two-way street.

Although some dispute the role of birds in transmitting Borellia, the Brinkerhoff team showed that 58% of the bird species evaluated may harbor Borellia and may infect black-legged ticks with the Lyme disease bacterium.  When an infected tick bites a human, the Borellia may be transferred and Lyme disease follows.

As global warming continues, the geographic range of black-legged ticks and the Lyme disease bacterium will shift northward.  Currently, there are only seven established populations of black-legged ticks in Canada.  Six are in southern Ontario and one in Nova Scotia.  The authors believe that these tick introductions were made by birds.

[First published on May 29, 2011]

Migratory Bird Treaty

By in Bird Conservation Tags:

I have lately heard of several instances where landowners are taking matters into their own hands and killing birds that they consider nuisances.  These reports involve recently returned songbirds like House Wrens whose energetic singing in the early morning disturbs peoples’ sleep and woodpeckers drumming on eaves or searching for insects in trees on a landowner’s woodlot.  Such killing is a federal misdemeanor and is punishable by a fine not to exceed $15,000 or imprisonment not to exceed six months for each bird killed.  The financial risks are therefore huge.  I thought today’s column would be beneficial in presenting information on federal laws related to birds.

These federal laws that protect our native birds were enacted in the Migratory Bird Treaty of 1918.  “Migratory bird” is taken to mean any native bird.  Specifically, there is a federal prohibition, unless permitted by regulations, for anyone to “pursue, hunt, take, capture, kill, attempt to take, capture or kill, possess, offer for sale, sell, offer to purchase, purchase, deliver for shipment, ship, cause to be shipped, deliver for transportation, transport, cause to be transported, carry or cause to be carried by any means whatever, receive for shipment, transportation or carriage, or export at any time, or in any manner, any migratory bird, included in the terms of this Convention . . . for the protection of migratory birds . . . or any part, nest, or egg of any such bird.” (16 U.S.C. 703).

Most states have similar regulations protecting native birds, such that violations may be both federal and state crimes.

Let’s break down this long federal statute.  First, it is illegal to kill a native bird.  Exceptions are gamebirds whose management falls under both federal and state control. In Maine, gamebirds include Ruffed Grouse, Ring-necked Pheasant, Wild Turkey, waterfowl, rails, American Woodcock, Wilson’s Snipe and Mourning Doves.  Such regulations set the hunting season and the maximum number of birds that can taken.  Federal and state hunting permits are required.

Ornithologists who wish to collect native birds for scientific research must obtain a federal Scientific Collecting Permit.  This permit requires that the applicant present strong evidence for the need for collecting birds.  Most states require a state collecting permit as well.  A Scientific Collecting Permit is also required if a person wishes to maintain wild birds in captivity.

Capturing a native bird requires a federal Bird Banding Permit and usually a state banding permit as well.  A Master Banding Permit is not easy to obtain.  One must first gain experience in removing birds from mistnets and handling birds.  The application form requires the endorsement of two Master Banders who can vouch for an applicant’s skill.  Then, the applicant must provide a sound scientific justification for the proposed research in which banding birds is required. Mistnets or traps for bird capture may not be purchased without a Master Banding Permit.

So far, we can see that federal and state laws prohibit the killing and capture of native birds without the appropriate permits to do so.  In the statute above, you can also see that it is illegal to possess a bird or any part thereof.   It is therefore illegal to have even a single feather of a native bird in your possession.  What’s the harm in picking up a bird feather you might ask?  The strictness of the statute makes sense from a regulatory point of view.

Imagine a man had a recently prepared mount of a Bald Eagle in his home.  When questioned about how he came to have the Bald Eagle, the man claims he found it dead on the roadside and used his taxidermy skills to mount the eagle in a lifelike pose.  One might suspect that this man may have shot the Bald Eagle, but has no proof.  With the “illegal possession” statute, the man would be in violation of the law.  Scofflaws could not make an end run around the stricture against killing native birds by claiming they found a specimen dead.  To possess whole birds, feathers or eggs, a federal Salvage Permit is required.

How about introduced birds?  They are not protected under the Migratory Bird Treaty.  Rock Pigeons, European Starlings and House Sparrows may be captured, killed or possessed without any legal repercussions.

Springtime heralds the return of the migratory birds from their winter homes.  The morning chorus of birds is beautiful to many people, but to some the exuberant singers disturb sleep and create too much music.  The good news for those people is that by mid-June the birds are nesting and much quieter.

[First published on May 15, 2011]

Review of Kaufman’s Field Guide: Advanced Birding; Eastern Bluebirds and Tree Swallows; Bird Hormones

By in Book Reviews, Field Guides, Physiology, Reproduction

In 1990, Kenn Kaufman’s Peterson Field Guide: Advanced Birding was published.  This book discussed the identification of difficult groups of birds like winter loons, scaup, medium-sized terns, hummingbirds and Empidonax flycatchers.  The book was peppered with Kaufman’s own pen-and-ink drawings.  The guide was meant to be a supplement to a field guide.

Now over two decades later, a greatly revised edition has been published.  It is fundamentally a different and better book than the first edition.  The new edition is still best used as a companion to a standard field guide.

The number of groups of confusing birds Kaufman covers is greatly expanded over the first edition.  Informative photographs are included within each group in lieu of the line drawings of the earlier edition.

One of the greatest strengths of the new edition is the 140 pages of introductory material, compared to only 19 in the first edition.  In this new edition, Kaufman offers a list and extended explanation of 13 principles of field identification.  A couple are “Always use multiple field characteristics” and “Consider the condition of the bird’s plumage”.

He then has an excellent section on feather tracts of birds and molting.  A sequence of photographs on the movement of feathers on an opening wing of a House Finch is brilliant.   In the folded wing, all the feathers one sees are greater coverts, tertials and the tips of the primaries.  As the wing unfolds, the other feather tracts become exposed.

Kaufman then presents sample illustrations of some birds (some at rest and some flying) to indicate the different feather types.  For each example, a photograph and a line drawing of the bird showing the feather tracts is shown.

Kaufman compares two schools of thought on field identification of birds.  One school relies on “general impressions of size and shape”, shortened to the acronym of giss. The other extreme is the fine detail approach where very close study of feathers, bill color and shape and other structures is required to yield a field identification.

In his coverage of the various problem groups, Kaufman uses both types of information to permit field identification.   For identification of swallows on the wing, Kaufman suggests watching swallows without using binoculars.  One can become familiar with the slight differences in flight behavior and the appearance of distinctive marks from varying perspectives.  The giss method can work here.

But for gulls, Kaufman advocates the fine detail approach, pointing out that the color of various feathers in the wings, tail and mantle are needed to be sure of an identification.

Eastern Bluebirds and Tree Swallows

Tree Swallow and Eastern Bluebird numbers are building in the state as their migration proceeds.  It’s time to make sure your nestboxes are in good shape.

Tree Swallows and Eastern Bluebirds compete for nestboxes.  How can you increase your chances of bluebirds nesting on your property?  You can take advantage of the fact that Tree Swallows are intolerant of other Tree Swallows nesting within 10 yards of their own nest.  So, if you put two nestboxes close together, one will not be used by Tree Swallows and is therefore available for bluebirds.

Bluebirds need quite a bit more space.  Typically, bluebirds will not nest with 200 yards of another bluebird pair.

People often wonder if they should remove the previous year’s nest from a nestbox.  Eastern Bluebirds prefer to reuse an old nest.  For Tree Swallows, removing an old nest has no effect on whether it will be used by Tree Swallows in the current year.

Hormones and spring

In mammals, the gonads (ovaries in females, and testes in male) remain the same size once adulthood is reached.  Not so in birds.  Because of the demands of flight, the ovary (most female birds only have one ovary) or testes of birds are greatly reduced during the non-breeding season.  Why carry around well-developed reproductive structures when those organs are not needed?  With increasing daylength, birds start to produce hormones: mainly testosterone in males and estradiol (an estrogen) in females.  These hormones cause the testes or ovary to increase greatly in size.  The size of a House Sparrow testis increases 500 times in the span of a month or so in the spring!

The huge increase in testosterone causes the males to become fiercely combative to other males.  One behavior common this time of year is to see a male songbird attacking its reflection in a mirror or window. Testosterone levels will decline in due time and the males will become less hyperactive.

[First published on May 1, 2012]

Earth Day

By in Bird Conservation

April 22 is Earth Day, a day when we should be particularly aware of our impact on the natural world.  Plants and animals cannot speak for themselves; concerned citizens must speak for the thousands of other species whose survivorship is threatened by human activities.

We’ll start today with a long view of earth’s history.  Using the fossil record, paleontologists have documented five mass extinctions.  During each of these episodes, at least 75% of existing species were driven to extinction.  The most recent mass extinction was about 65 million years ago when the dinosaurs, pterodactyls and the large marine plesiosaurs were wiped out.

Paleontologists do not fully understand the cause of most of these mass extinctions although changes in climate and volcanic activity seem to be likely candidates.  We do have better understanding of the most recent mass extinction that resulted in the elimination of the dinosaurs.  An asteroid, probably about six miles in diameter, hit the earth.  The crater has been found off the coast of the Yucatan peninsula in Mexico.   The ash from the collision would have greatly reduced photosynthesis by plants, disrupting the food web of that era.

A recent article in the journal Science by Anthony Barnosky and colleagues suggests that we are at the beginning of a sixth mass extinction.  This time, the cause is clear.  Humans are causing the extinction of many species by removing natural resources from communities, destroying and fragmenting habitat, and facilitating the introduction of non-native species.  The authors argue that 75% of existing species could be driven to extinction in the next few centuries unless humans reverse our ways and become better stewards of the earth.  That is a sobering claim.

We know that birds are especially sensitive to environmental degradation and habitat loss.  Conservationists often use birds as indicator species.  If a particular indicator species is doing well, then other associated species that are less sensitive are probably doing fine as well.  If a habitat starts to degrade because of human impacts, a change in the survivorship or reproductive success of birds will be one of the first signs.

As Earth Day approaches, what are some of the things you can do to help protect the birds?

Share your interests in birds with other people who haven’t been exposed to the wonders of birds.  People are often amazed to learn of the many birds all around them that they were never really aware of.   Young people often become eager birders once they see how much fun birding can be.

Make your property more bird-friendly. All birds need water so a water bath or pool will help the birds. Brushpiles are great habitat for sparrows.

Feed the birds.  Abundant evidence shows that feeding birds increases their survivorship.  Birds do not become dependent on human handouts so don’t worry if you can’t maintain your feeding station continuously.  Keep your feeders clean; bird diseases can spread rapidly at a frequently used feeder.

Join Partners in Flight.  This program depends on the work of thousands of people interested in birds throughout the Americas.  Join and find out what you can do to help conserve birds. Information can be found on the WorldWideWeb at: http://www.partnersinflight.org/

Join the American Bird Conservancy.  You can find information on this very effective conservation group at http://www.abcbirds.org/

Contribute to or join other conservation groups like the Nature Conservancy, the National Audubon Society, Maine Audubon Society, the World Wide Fund for Nature, the Sierra Club or the Appalachian Mountain Club.

Do your best to conserve resources: water, gasoline, paper, any other consumable resource.  We can reduce our effects on the natural world by reducing the amount of tree harvesting, oil mining and other removals of natural resources.

When you travel to go birding, considering purchase carbon offsets for the amount of carbon dioxide your car or jet transportation releases into the air.  Carbon offsets might be an investment in a solar energy plant or funding to plant trees that will absorb carbon dioxide and convert it to new plant tissue.  You can find lots of carbon footprint calculators on the web.  One I like is: http://www.terrapass.com/carbon-footprint-calculator/

If you are a coffee drinker, purchase shade-grown coffee.  Most coffee is grown on huge plantations in which the natural tropical forest has been clear-cut to allow coffee bean plants to grow. These coffee plantations have a very low diversity of birds. Some coffee bean plants grow well in the natural forest in the shade.  Supporting growers that use shade-tolerant coffee bean plants protects habitats and therefore birds.  A useful website can be found at: http://www.coffeeresearch.org/politics/birdsafe.htm

[First published on April 17, 2011]

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