Parasitoid Wasps; Insect Migrations

By in Insects

Wasp Parasitoids

Every now and then, I devote a column to a different group of flying animals, the insects.  We’ll recognize the insects as honorary birds today.

This column was precipitated by an interaction I saw last weekend while I was mowing the lawn.  I saw a black wasp interacting in the grass with what I thought was perhaps a second wasp.  Going closer, I realized the wasp was attacking a large wolf spider.  This interaction was the beginning of a fascinating but macabre relationship.

SpiderThe spider, at least five times the size of the spider wasp (family Pompilidae), tried to escape as the wasp injected a neurotoxin into the spider.  The toxin quickly took effect and the spider was paralyzed.  The wasp then quickly dragged the spider to the side of our house.  It walked up a granite foundation stone and underneath the lowest cedar shingles.

The rest of this tale will take place sight unseen.  The wasp will lay one inside the paralyzed spider.  Though paralyzed, the spider will live.  The wasp egg will hatch inside the spider and the larva will eat the internal organs of the spider.  The wasp larva will eventually pupate, later emerging as an adult.  Maybe I should have saved this story for a Halloween column!

Entomologists classify wasps like the one I saw as a parasitoid. Unlike a true parasite, a parasitoid either kills or sterilizes its host.  The wasp I saw is hardly unique.  Many wasps, in  dozens of families, are parasitoids.  Some lay eggs on other insects but wolf spiders are commonly used.  Wolf spiders typically do not build webs.  A spider’s web is used primarily to capture prey but offers a secondary benefit of protection from wasps.  The free-ranging wolf spiders are therefore at risk to parasitoid wasps.  I may have unwittingly caused the demise of the spider by cutting the grass and making the spider easier to see.

 Migration

Bird migration is near its peak now.  We can predict the order of departure in the fall: first the swallows and flycatchers, then the warblers, then the sparrows and hawks.  Migration implies a predictable, seasonal movement.  Animals may engage in nomadic wanderings are not predictable enough to warrant as migration.  For instance, White-winged Crossbills wander widely to find bumper crops of conifer cones.

Although birds are the best migrants, they do not have a monopoly on migration.  You have no doubt seen videos of wildebeest, zebras and other mammals migrating to and from the Serengeti Desert.

Some insects migrate as well.  A widely distributed dragonfly, the Wandering Glider, occurs on six continents.  Populations in Africa migrate to India after the monsoon season starts.  The abundant rains provide ample opportunities for the females to lay eggs in aquatic habitats.

Some butterflies migrate as well.  In North America, the best known migrant is, of course, the Monarch.  Any Monarchs you see this fall will attempt to fly south to a small pine forest in mountains in northwestern Mexico.  Even they can make it to the wintering grounds, they will not return.  The complete migration from Mexico back to Mexico the following year requires five or six generations!

Originally published on September 14, 2014]

The Extinction of the Passenger Pigeon

By in Bird Conservation, Identification, Morphology, Species Accounts

We are coming up on the 100th anniversary of one of the sad days in ornithology.  On September 1, 1914, the last remaining Passenger Pigeon, a female named Martha, died in captivity in the Cincinnati Zoo.  A species that had been astoundingly abundant had vanished from the earth.

martha_2002-3499_600w

Photo of Martha taken by Carl Hansen, Smithsonian Insitution, 1985.

Passenger Pigeons had a large range in eastern North America, spanning eastern Canada south to the Gulf coast and west to western Texas and Montana.  They resembled the Mourning Dove but were much larger, up to 17 inches long.  Their feathers glowed with red, gold and blue iridescence.  The word passenger in their name refers to their migratory tendencies, not to their use in carrying messages for humans.

Passenger Pigeons were undoubtedly once the most abundant bird in North America.  In the early part of the 19th century, Passenger Pigeons were more abundant than all other North American birds combined!  There is a report of one flock that contained over two billion birds.   Audubon reported a migrating flock of Passenger Pigeons in Kentucky that blackened the sky for three days.  Some nesting colonies were 20 miles across.  Such numbers boggle the mind.

In Maine, Passenger Pigeons were summer residents.  They were abundant until 1820 or so and were common enough to provide successful hunting until around 1850.  The first record we have of Passenger Pigeons in Maine dates from the French explorer Samuel Champlain who found them on islands near Cape Porpoise in what is now York County.

Why did this species go extinct?  The answer is probably obvious: humans.  A large industry developed in the 19th century to provide Passenger Pigeon meat for the tables of European immigrants to the United States.  Because of the pigeons’ flocking and colonial nesting behavior, they were easy targets.  Large numbers of pigeons could be harvested with ease.   Some were caught in nets, others fell to the ground after being smoked with sulfur fires, yet others were killed by guns.  Special guns, precursors to machineguns, were developed to allow large numbers of pigeons to be killed quickly.

The harvest of what seemed like a nearly infinite resource was not regulated.  The development of railroads, providing a fast way to get pigeon meat to eastern markets, drove the hunting to an even greater intensity.   By the middle of 19th century, several thousand people derived a livelihood from harvesting and selling Passenger Pigeons.  One processing plant in New York handled 18,000 birds a day.  A billion birds were harvested in a single year in Michigan.

But how could the most abundant bird in North America be harvested to extinction?  As the population started to decline, one would expect the industry to collapse, giving the ravaged Passenger Pigeon population a chance to recover.  The answer appears to lie in the highly social nature of the species.  The gonads of most birds regress to about a fraction of their active size during the non-breeding season.  Changing day lengths cause birds to increase their sex hormones and their gonads enlarge.  Rather than increasing day length, the cue for Passenger Pigeons to enlarge their reproductive organs and initiate nesting was the social stimulation of lots of other Passenger Pigeons in a local area.  Without a large enough concentration of birds, the reproductive cycle did not begin.

The collapse of the Passenger Pigeon started around 1880 and commercial hunting, no longer profitable, ceased.  Unfortunately, the large flocks of Passenger Pigeons were dispersed across the continent in smaller groups.  These flocks may never have gotten large enough to induce the beginning of the nesting cycle.

The population continued to decline and was extinct in the wild until 1900.  The last Passenger Pigeon reported in Maine was shot in Dexter in 1896.  Efforts to breed the species in captivity failed.  Martha was the last of her species, gone 100 years ago.

[Originally published on August 17, 2014]

More on Feather Pigments

By in Physiology

In the last column, I wrote about the melanin and carotenoid pigments that birds embed in their feathers to impart color to the plumage.  Melanins are manufactured by the bird while carotenoids must be acquired from the diet.

Porphyrins are a third type of feather pigment.  Porphyrins can make red, brown, green and even pink colors in a variety of bird species.  The brown colors of many owls are caused by a combination of melanins and porphyrins.  Pigeons and grouse have porphyrins as well.  Porphyrins produce the green plumage in a group of African birds called the turacos.

Porphyrins are created by birds by stringing together amino acids.  The structure of porphyrins is actually quite similar to hemoglobin.

One cool aspect of porphyrins is that they are bright red under ultraviolet light.  Birds’ color vision allows them to see into the ultraviolet portion of the spectrum, an ability we mammals do not have.  Porphyrins must be much more vivid as seen through the eyes of a bird.

A group of birds from New Guinea called the pitohuis have black heads and an orange body, an indication that they deposit both melanins and carotenoids in their feathers.  But the Hooded Pitohui and Variable Pitohui go one step further by adding poisons to their feathers!

This remarkable phenomenon, well know to New Guinean natives, was only appreciated by western scientists about 20 years ago.  Jack Dumbacher, then an ornithology graduate student, caught some pitohuis in his mist nets.   After handling the birds, he had a sneezing attack as well as tingling in the hands.  He was able to show that the feathers and skin of the pitohuis have a potent toxin related to the deadly toxin produced by some poison arrow frogs.  The pitohuis acquire the toxins from their favored beetle prey and sequester it for their own use.  The nasty toxins in the feathers may function in repelling ectoparasitic mites and insects as well as discouraging snake, raptor and mammal predators.

But how about the blue coloration of a Blue Jay or Indigo Bunting or the green coloration of a parrot?  Those colors are produced by light interference rather than by an actual pigment.  We classify the blue of a Blue Jay as a structural color.

Small pockets of air within the feathers of any bird with blue coloration scatter the incoming light (a mixture of all the colors of the rainbow).  Shorter wavelengths are scattered more than longer wavelengths.  So, the blue wavelengths are scattered to a greater degree than the other colors so the blue wavelengths are the ones we see.

In parrots, the vacuoles have a different shape to maximize the scattering of the green wavelengths.  The primary color scattered back from such parrots is therefore green.

Because the light is scattered in all directions, the blue or green color will appear equally vivid from any viewing angle.

The shimmering of a hummingbird’s throat (the gorget) or the shimmering of the eyespots of a peacock’s tail relies on a different kind of interference.  The iridescent colors in these birds change with the angle of view.  These colors are also quite bright.  The shimmering of the colors of a male hummingbird’s gorget as it twists is head is simply stunning.

Rather than having simple vacuoles, a hummingbird feather has a complex vacuole system consisting of several sheets of vacuoles stacked one on top of the next.  As light is absorbed by the vacuoles, light scattered from one portion of the structure interferes with light scattered from another portion.  Sometimes, these interactions cancel each other out and sometimes they are in perfect synchrony, leading to bright colors.  The gorget of a hummingbird can range from black to dull red to bright red depending on the angle of the observer.

[Originally published on August 3, 2014]

Feather Pigments and an Albino Robin

By in Uncategorized

The topic of this column and the next was inspired by an email from Lisa Jones.  She sent me a video of an albino American Robin in her backyard in Clinton.  You can see the video in another post on this website.

The robin that Lisa found is a pure albino.  All of the feathers are white and eyes are red.

Many birds, of course, have feathers of strikingly different colors.  Rose-breasted Grosbeak males are stunning birds with black, white and red feathers.  Ducks, especially drakes, often have many different hues in their feathers.  A Green-winged Teal is nice example.

How are these feathers colored?  We need to realize that a fully formed feather has no living tissue associated with it.  During the formation of the feather, tissues in the feather-forming structures called follicles form the intricate shape of the feather to be.  The cells in the follicle tissues secrete keratin, the same basic material in your fingernails.  Once the complex feather is formed from the secreted keratin, the follicle cells withdraw, leaving the non-living keratin behind.  A feather is produced!

Often, follicle cells lay down pigments in the developing feather.  The most common type of pigment is melanin.  Melanin gives a feather dark coloration (black, browns, grays).

A bird is able to manufacture the melanin it needs to color it feathers.  In the process of digestion, proteins are split into their basic units of amino acids.  A protein is nothing more than a long chain of amino acids.  One of these amino acids is tyrosine.   Birds use tyrosine to manufacture melanin.

The follicle cells intersperse melanin granules in the keratin secreted to make a feather.  A feather with no melanin or other pigments appears white because all wavelengths of light are reflected back to a viewer.  Dark melanins absorb all the wavelengths of visible light and hence are black to our eyes.

In addition to providing color, melanins also appear to strengthen the feathers.  In a flying bird, the primary feathers at the tips of the wings undergo pronounced deformation during the downward stroke of powered flight.  The tips of larger birds are often richly endowed with melanin.  Snow Geese, American White Pelicans, Northern Gannets, Wood Storks, American Bitterns, and most species of gulls provide only a partial list.

The glorious yellow of an American Goldfinch, the brilliant orange of a Baltimore Oriole and the vivid red of a male Northern Cardinal are produced by a different type of feather pigment called carotenoids.  Carotenoids are plant pigments used in the process of photosynthesis.  Birds cannot manufacture carotenoids so must recycle the carotenoids from their food.  The pathway of carotenoid acquisition can be complicated.  For instance, flamingoes are pink because they sequester carotenoids from their small shrimp prey, which in turn get the carotenoids from the unicellular algae growing in saline lakes.

Have you ever seen a House Finch male that was dull orange rather than red?  Such a washed-out bird is not acquiring enough carotenoids in its diet to make deep red breast and head feathers.  Animal behaviorists call the intensity of the coloration an honest signal.  A Scarlet Tanager with stunning red colors is advertising its ability to forage effectively.  That red coloration can’t be faked.  On the other hand, a Scarlet Tanager with a washed out appearance is advertising its poorer foraging abilities.  Which male do you think a female Scarlet Tanager would choose for a mate?

Scarlet Tanagers use their carotenoid resources wisely.  Their contour feathers only have red carotenoids at the tips.  Since the contour feathers overlap like shingles, only the outer tip of each feather is seen.  There is no benefit in coloring parts of feathers that will never be seen. Female Scarlet Tanagers have an olive-green color.  This color represents an interaction of melanin and carotenoid pigments in the same feathers.

[Originally published on Jul 20, 2014]

Three New Books on Insect Identification

By in Uncategorized

I contend that birders today are better overall naturalists than birders 20 years ago.  Birders today are often proficient at identifying dragonflies, damselflies, and butterflies that go whizzing by as we have our binoculars at the ready.  A plethora of field guides to various insect groups has facilitated this welcome growth in the expertise of birders in other groups of animals.  Butterflies through the Binoculars and Dragonflies of the Binoculars played the role of the first Peterson guide, opening up new challenges for field identification.

In today’s columns, I want to review three remarkable guides to three groups of insects.  All of these books are published by Princeton University Press, a press with a strong dedication to books on natural history.

The first is Dragonflies and Damselflies of the the East by Dennis Paulson.  This guide covers all 336 species of the order Odonata found in eastern North America.  Maine has 158 species of odonates: 47 damselflies and 111 dragonflies.

Like most field guides, the Paulson guide begins with a brief overview of odonate biology and then covers the morphological features that are used in field identification.

The bulk of the book is the species accounts.  Paulson provides a map, at least one color photograph and text giving a description of each species, the features used for identification, habitat, and flight season.

Field identification of some odonates is easy.  The Widow Skimmer and Twelve-Spotted Skimmer can be recognized with the naked eye.  Others require a closer look through binocularsPaulson and some are so similar that capture and examination with a hand lens may be necessary to clinch a identification.   Paulson’s book provides the guidance you will need to become proficient odonatologist.

If 158 species of odonates seem overwhelming, how about bumble bees?  Paul Williams and colleagues have written a guide called Bumble Bees of North America.  Bumble bees are common insects but not that diverse.  Only 46 species are found in North America and only 20 in Maine.

The authors provide a nice overview of bumble bee biology in the first part of the book.  The life cycle of cuckoo bumble bees is particularly fascinating.  Like their namesakes, cuckoo bumble bees dupe other species of bumble bees into providing for their own young.

bumble beesEach species is discussed in turn with a list of hand characteristics (most of which can be easily discerned from a photograph) and microscopic characteristics.  A range map and photographs are provided.  The abdomen banding is important in identification and can vary among queens, workers and males.  A clever diagram showing the range of variation for each type is very useful.

Bumble bees are important pollinators, particularly early in the spring.  These insects also pollinate many woodland and high mountain flowers.  Sadly, bumble bee numbers are declining.  Learning to identify bumble bees is the first step in monitoring the status of these fascinating creatures.

Insects are far and away the most diverse group of animals on earth.  Within the insects, he beetles are the most diverse order with 400,000 species described.  In turn, the weevils with 60,000 species are the most diverse family of beetles.  Identification of beetles to species is daunting to say the least.

k10218However, learning to recognize beetle families is an achievable and satisfying goal.  Attaining that goal can be accomplished with  Arthur Evans’ Beetles of Eastern North America.  A weighty tome, this book is a pleasure to hold and behold.  Each family of eastern North American beetles is described with a description of the diagnostic features of each family.  Then, the author provides a number of examples of species in that family each with a superb color portrait.  The pictures are truly stunning.

Add in an excellent introduction on finding beetles, general beetle biology, rearing beetles and starting a beetle collection and you have a marvelous resource for the study of the Coleoptera.

[Originally published on July 6, 2014]

Song Variation

By in Vocalizations

June is a wonderful time a year for birders with the air filled with the marvelous songs of many birds.  The morning chorus is truly a feast for the ears.

Let’s start by considering the important distinction between a bird song and a bird call.  Songs are complex vocalizations, usually associated with reproduction.  Males sing and females typically do not although Northern Cardinal and Painted Bunting females are among the exceptions to the rule.

Calls on the other hand are simple vocalizations, usually given by all members of a species.  The calls are generally instinctive so do not need to be learned.  Calls can be used to keep contact with other flock members and to sound alarms.

The largest order of birds is the Passeriformes, often shortened to the passerines.  The passerines contain 60% of all bird species.  The passerines are subdivided into two major groups: the suboscines (flycatchers and their relatives) and the oscines  (songbirds).  Suboscines have very simple songs like the “FEE-bee” song of the Eastern Phoebe.  The songs of suboscines are innate so do not need to be learned.  Oscines with must generally learn their complex song from their father or a neighboring male.

Songbirds comprise some 4,000 species, many of which are vocal virtuosos.  However, songs are known in other orders of birds.  Hummingbirds are one such group.  Anna’s Hummingbird has a 10-second long song, pretty impressive for such a small bird.

In the last column, I wrote about the cheating that often goes on with birds in a seemingly monogamous relationship.  Not surprisingly, bird song plays a role in these soap operas.  A male sings for two reasons: to attract females to his territory and to warn other males to stay out of his territory.

In some birds, distinctive songs are sung for these two functions.  The Black-throated Green Warbler provides a nice example.  Male song is often written as “zee-zee-zee-zoo-zee” with the final zee given with great emphasis.  This song is referred to as the accented song.  It is sung for the purpose of attracting a female.  The male is essentially proclaiming his bachelor status and desire to enter into a relationship.

An alternate song is heard that can be rendered as “zee-zee-zoo-zoo-zee” or “trees-trees-whispering-trees”.  This song is called an unaccented song and is directed at neighboring males to deter those males from visiting a male’s territory and perhaps mating with his partner.

You may find it useful to visit www.allaboutbirds.org and search for Black-throated Green Warbler.  Click on the Sound tab.  The first song is the accented song and the second is the unaccented song.

Chestnut-sided Warblers provide another example of males that have both an accented and unaccented song.  The accented song is often written as “pleased-pleased-pleased-to-MEETCHA”.  The unaccented song lacks the explosive final two syllables.  The allaboutbirds.org site has a recording of the accented song.

Some songbirds vary their song over the course of a day.  American Robins are usually the first local species to start singing in the morning, often as early as 3 PM much to the dismay of some would-be sleepers.  The song of a robin is a series of two- and three-note phrases, delivered in a sing-song style.  The dawn version of the song is generally a bit faster.  The birds also include a soft, whisper-like phrase that is aptly described as “hisselly”.  During the later part of the day, the song is sung more slowly and the “hissely” phrase disappears.  We have no idea at this point of the importance of the “hissely” phrase.  The allaboutbirds.org site has recordings of both the dawn song and the daytime song.

Eastern Phoebes sing their fairly simple “FEE-bee” song during most of the day.  However, early in the morning, they add an extra syllable, to sing “FEE-buh-bee”.  Listen for that variation from your local phoebe.

[Originally published on June 22, 2014]

Molting

By in Migration, Physiology, Reproduction

Now is the time of year when I start looking closely at American Goldfinches. During the winter, females and males are difficult to tell apart. The dark on the wings is black in males and dark brown in females. The wing bars, particularly the upper one, are a bit more yellow in males. In a month, telling males from females will be easy. The bright yellow body and the black cap on the forehead leave no doubt that such a bird is a male in his summer finery.

The transformation occurs through the process of molting, the replacement of older worn feathers, pushed out by newly formed feathers from below. Molting is essential because feathers, marvelously light and strong, do wear down. These feathers must be replaced as they abrade or flight would be difficult and insulation poor.

With over 11,000 species of birds in the world, generalizations about molting are hard to make. Most birds do molt their contour feathers (their wing feathers, tail feathers and the large body feathers) twice a year. A bird usually molts all of its contour feathers in a sequenced fashion in the fall, leading to its basic plumage. In the spring, another molt occurs leading to the alternate plumage, the plumage of the breeding season. Our American Goldfinches will soon be molting into their alternate plumage. The spring molt is often with the head, body and sometimes tail feathers replaced.

The distinction between basic plumage and alternate plumage can be dramatic as in the warblers, tanagers, and Rose-breasted Grosbeaks. The two plumages are similar in other birds such as gulls, sparrows, wrens, chickadees and nuthatches. Those birds with similar alternate and basic plumages still undergo two molts a year, despite their seemingly unchanging appearances.

Molting requires a significant amount of energy. The only activities in a bird’s life that rival the energetic cost of molting are nesting and migration. Each activity pushes a bird to its limit. No bird can do two of these three activities at once. A typical pattern for a migratory bird is molt into alternate plumage (often a partial molt), migrate north, nest, molt into basic plumage, and migrate south.

Here are a couple of examples that demonstrate the energetic demands of molting. Some Peregrine Falcons breed on the arctic tundra. The short arctic summer is not long enough to allow the falcons to nest and then molt into basic plumage. After nesting, the falcons begin a molt, replacing some of their flight feathers. They then migrate to their wintering quarters, forced south by the deteriorating weather. Once in their winter quarters, they resume their molt.

Yellow-breasted Buntings have a broad breeding distribution in Europe and Asia, stretching from the arctic tundra to central China. They winter in Southeast Asia and India. Like the arctic Peregrine Falcons, the brief arctic summer does not allow enough time for the buntings to nest and then molt before migration. Those high latitude birds migrate immediately after nesting to the lower Yangtze area of China. In that moderate climate, the birds undergo a complete molt and then continue their migration south on fresh feathers. Buntings nesting in the southern part of the breeding range have plenty of time to nest and then molt before they embark on their southward migration.

Two of our local bird species transform themselves from basic to alternate plumage without molting. The dorsal black coloration of breeding Snow Buntings is actually present in basic-plumaged birds. As the winter proceeds, the back feathers of a Snow Bunting erode, exposing the black coloration along the middle portion of each feather. The black is hidden in the winter by the shingle-like arrangement of overlapping feathers. The white spangles on winter Eurasian Starlings are eroded in the same way, leading to the black alternate plumage. Ornithologists call this phenomenon molt by wear.

 

[Originally published on June 8, 2014]

Satellite Males, Infidelity and Delayed Plumage Maturation

By in Behavior, Reproduction

Spring migration is winding down.  The arrival of Blackpoll Warblers, Black-billed Cuckoos, Saltmarsh Sparrow and Nelson’s Sparrow signifies the end of the spring spectacle.

Having returned to Maine from the south, male birds are setting up territories and trying to attract a mate with songs and displays.  We have a tendency to project an idyllic image of a happy bird couple raising a family.  That image is often inaccurate.

For starters, not every bird will be able to find a mate.  Some of the best evidence for this statement comes from an experiment that was done in Maine over 50 years ago.  The methodology of the study will be reprehensible to some.  Nevertheless, we learned much from this experiment.

The researchers mapped out a 40-acre forest plot.  In early June, they determined that 154 territorial birds (males) were present.  Then the removals began.  The researchers shot as many of the singing males as they could.  Within two weeks, the density of male birds was reduced to 21% and kept at that level until July 11. By July 11, 528 adult birds had been killed.  That’s 3.5 times the original density of birds!

This removal experiment tells us there are lots of unmated males that are lurking around, hoping for a chance to acquire a territory and a mate.  These non-territorial birds are called satellite males in the ornithological literature.  The experiment shows that there must be many satellite males waiting for an opportunity.

As in mammals, birds show a 50:50 proportion of females:males.  With so many satellite males, there must be unmated females present as well who never come into the vicinity of an unmated male.  The failure of some birds to find a mate challenges our fanciful notion of wedded bliss in birds.

An even greater challenge to that notion lies in the fact that avian social life has soap opera aspects.  Cheating on a mate occurs frequently.  Thanks to the development of DNA fingerprinting techniques, we can determine the paternity of nestlings.  Although 90% of bird species are classified as monogamous, 30% of nestlings are sired by a male other than the female’s mate.

It’s a two-way street.  Females seek multiple partners to fertilize their eggs and males seek as many female partners outside of the pair-bond as they can find.  These dalliances are referred to as extra-pair copulations and their importance in the field is indicated by the fact that every ornithologist knows the initialized version, EPC, of this behavior.

The male incentive for EPCs is clear: to father as many baby birds as possible.  What’s the advantage for a female who can produce only a few eggs?  The best argument is that the female is seeking to increase the variability of her nestlings.  The environment is always changing and having greater variation in her offspring increases the chances that one or two of those offspring will better fit the demands of the environment in the future.

The reproductive life of a territorial male is pretty good.  He fathers at least some of the eggs laid by his mate and perhaps has some EPCs with females on neighboring territories.  But what about those unmated satellite males?  Do they get to reproduce at all?  Satellite males do not have a territory because they are outcompeted by the stronger males who can defend a territory.  Weaker males are usually younger as well.

Some males engage in a type of trickery called delayed plumage maturation.  In the second year of their life, their plumage resembles that of a female.  This disguise allows them to slip into the territory of a male (he’s got cheating on his mind) and sneak a quick mating with the resident female.  Check your field guide to see the second-year plumage of American Redstarts, Baltimore Orioles and Red-winged Blackbirds.

[Originally published on May 25, 2014]

Human-related Mortality of Birds – IV

By in Bird Conservation

The last three columns were devoted to a consideration of the various human-related sources of bird deaths.  Perhaps because some readers read only one or two of the columns, I have gotten many emails that indicate I failed to get across the point I wished to make.  The columns were timed to lead up to Earth Week.  But we should not try to tread lightly on our planet for only a week a year so I will provide this overview column.

Let’s consider loggerhead turtles as an apt analogy for the importance of understanding the impact of different sources of death for a species.  Loggerhead turtles are an endangered species.  Some are killed illegally for food, others are trapped in trawl nets by commercial fishing boats, and predators get some hatchlings are they stumble down the beach after hatching for their first swim in the ocean.  Nests on sandy beaches are often lost to predators including dogs.

For decades, conservationists have monitored the arrival of loggerhead females on nesting beaches.  These people may cordon off the nest site to keep egg predators away.  Hatching turtles may be accompanied by humans as the turtles head to the water for the first time.  These efforts have saved many turtle lives.

However, modeling the population dynamics of loggerhead turtles revealed some intriguing truths.  First, even if every egg were to hatch and every hatchling could make it to the water, the loggerhead turtle would still go extinct under present conditions.  The model further showed that the critical stage of the life cycle is the 5-7 year-old turtles.  Many of these turtles died from becoming entangled in trawl nets; the turtles drown when trapped in a net.

To reduce these deaths, the federal government is mandating that trawlers, fishing in areas where loggerhead turtles occur, must have turtle excluder devices (TEDs) installed on their nets.  When a turtle is captured in a net, the TED opens up to allow the sea turtle to escape.  The power of the model lies in showing environmental managers which stage of the life cycle should be targeted for conservation efforts.  Protecting the 5-7 year old juveniles is more effective than protecting eggs.

Reducing human impacts on bird deaths requires a similar approach.  We need to understand the magnitude of the different types of human-related mortality.  The last column described by far the two most potent sources of bird deaths related to humans: building collisions and cats.  My argument is that we should be trying to reduce these hazards first because of the sheer magnitude of the effects.  As an unabashed cat lover, I know that keeping cats as indoor pets is the way to go for the safety of many birds and the safety of the cats.  Proper placement of bird feeders and improving the visibility of glass in our houses can reduce collision-related bird deaths.

Do I therefore disregard deaths from wind turbine collisions?  Of course not.  As indicated earlier, I am a long-time opponent of mountain-based wind farms.  Any bird death from human causes should be of concern.  Collectively, wind farms result in far fewer deaths than cats or building collisions.  However, we need to realize that wind turbines pose threats to some species like cranes and eagles that are not likely to die from a cat attack (!) or a window collision.

We all need to take energy conservation more seriously.  Better yet, we should be practicing energy avoidance.   We can thereby reduce the need for more coal-burning power plants pumping carbon dioxide into the atmosphere as well as wind farms and hydroelectric dams that cause the loss of habitat.

Birding locally reduces bird deaths from car collisions and cuts down on carbon dioxide emissions.  Buy a carbon dioxide offset to mitigate the carbon dioxide released from your car or plane travel.

[Originally published on May 11, 2014]

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