June 2008

For the Birds: Spring Migration; Hog Island Camps; Maine Butterfly Survey

Migration

The marvelous spectacle of spring migration is here. Soon, the Black-billed Cuckoos, Blackpoll Warblers and Yellow-bellied Flycatchers will arrive in good numbers. The appearance of these late-arriving species signals the end of the spring migration.

Today, I want to consider why birds migrate. Each spring, several billion birds stream into North America from Caribbean islands, Central America and South America where they have spent the winter. Why do so many birds undertake these arduous migrations? The benefits must exceed the costs. What are the benefits migrating breeders receive?

To answer these questions, we have to understand both why birds migrate north to breed and why they leave their northern breeding grounds to return to tropical or subtropical areas. The explanations stem from the fact that the earth is tilted on its axis.

Let’s start with equatorial regions. Despite the tilt of the earth, equatorial regions have twelve hours of daylight each day. As one proceeds north, the length of day and night becomes unequal. When the northern hemisphere is tilted toward the sun, we have summer and temperate regions have day lengths that increase as one moves toward the North Pole.

The long summer days mean that plants can photosynthesize for sixteen hours or more each day, longer than plants at the equator. So during the northern summer, plant production spikes, providing food for insects that in turn provide food for birds. During the northern summer, food availability in temperate regions may exceed that of tropical regions. Birds migrate to the north to take advantage of the summer flush of food. The further north one goes, the longer the day length and bigger the spike in plant growth.

All good things must come to an end and the movement of the earth around the sun ultimately leads us to autumn with ever-shortening day lengths. Plant production decreases as light becomes less available and temperatures fall. Insect abundance declines. Many migratory breeding birds depend on insects so must leave for southerly areas to avoid starvation.

The cost of migration is more than paid for by the abundance of food in the summer at higher northern latitudes. But not all tropical birds migrate. What are the costs and benefits of staying put? The benefit is the energy saved by not migrating. The cost is that competition for food is very high in the tropics and destruction of nests by predators is very high. Tropical birds typically have multiple nests each season with a modest number of eggs, most of which are doomed to failure.

Hog Island Audubon Center

A landmark of environmental education since 1936, Hog Island Audubon Center’s residential programs educate, adults, children and families about coastal wildlife in Maine. The sessions are based on a 330-acre island in midcoast Maine’s Muscongus Bay. The sessions are led by some of the world’s most respected naturalists and environmental educators. You can find more information about their offerings at: http://www.maineaudubon.org/explore/camp/hi_overview.shtml

I want to call your attention to a new session called Family Birding Adventures geared for families with kids between the ages of six and thirteen. One of the highlights of the week will be a trip to Eastern Egg Rock to see nesting Atlantic Puffins. The session will be led by Jason and Laura Guerard, naturalists from the Cape May Bird Observatory. Jason and Laura met on Hog Island and Jason later proposed to her there. For more information, visit the website above or call (888) 325-5261 ext. 215.

Maine Butterfly Survey

The Maine Butterfly Survey, a five-year project to map the distribution and abundance of the butterflies and skippers of Maine, has begun its second year. This project relies heavily on volunteers. The first year yielded over 1500 records (specimens or photographs). Volunteers established four new state records and a large number of county records in the first year of the project. Two volunteers photographed Pipevine Swallowtails in late September 2007. These two records represent the first records of the species since 1907. You can see all of the 2007 records at the MBS website: http://mbs.umf.maine.edu/

As the Volunteer Coordinator for the project, I would like to encourage you to participate in the project. All participants are asked to attend a training workshop. Each workshop participant will be given equipment, a handbook and voucher forms. The last 2008 workshop will be held on Saturday, June 21 at Colby College in Waterville. The workshop will begin at 9:30 and conclude around 2:30. Lunch will be provided. If you are interesting in attending the workshop, please email me to reserve a spot. Enrollment is limited.

[originally published on May 17, 2008]

For the Birds: New Bird Books for Beginning Birders

The spring migration is perhaps the most exciting time of year for North American birders. After a long Maine winter, the sounds of the first Eastern Phoebes and Red-winged Blackbirds and the sights of colorful warblers hold the promise of a glorious Maine summer. There is nothing like a spring birding excursion to hook a novice on birding.

Two books geared for beginner birders have recently appeared. One is meant for adults and one for kids. I’ll review the two books in today’s column. Perhaps, you have a friend or family member who might appreciate a copy of one of these books.

Finding Your Wings, written by Burton Guttman, is a different kind of book in the Peterson Field Guide series. This book is really a workbook designed to help a person new to birding to learn how to really look at birds how to identify them. Along the way, a diligent user of Finding Your Wings will learn much about bird behavior, classification and the etiquette of birding.

This workbook is designed to be used in conjunction with a field guide of North American birds. The workbook is specifically written to accompany either Roger Tory Peterson’s A Field Guide to Birds of Eastern and Central North America or A Field Guide to Western Birds. However, any North America field guide can be used in conjunction with Finding Your Wings.

The workbook begins with basic principles and skills of birding, continuing with an overview of the major bird orders and then more detailed descriptions of the topography of birds. Other chapters deal with molting, identifying birds in flight and learning to identify birds by their songs or calls. The book concludes with six chapters on groups of birds that pose particularly challenging identification problems. Bird groups covered include hawks, shorebirds, gulls and sparrows.

The content of the book sounds like standard fare for a birding book. The unusual, and I think innovative, aspect of Finding Your Wings is the activities and quizzes that fill the book. Doing the activities and taking the quizzes is key to getting the most out of the workbook.

Four kinds of activities are used in the workbook. Indoor Exercises require the reader to refer to a picture provided or pictures in a field guide to answer questions. A reader might be asked to look at the account for a Clay-colored Sparrow and then write down a description of the head of the bird. In so doing, the reader would learn the names of distinctive markings like the supercilium, auricular stripe and malar stripe. Answers are provided at the end of the book.

Field Exercises require the beginning birder to make observations in the field, such as determining the wing beat rate of different birds. Quizzes allow readers to test their knowledge gained from the Indoor and Field Exercises. Finally, several Games are described that are great for social learning.

The second book, also in the Peterson Field Guide series, is called The Young Birder’s Guide to Birds of Eastern North America by Bill Thompson III. This field guide was developed with the advice of Thompson’s 11-year old daughter and other members of her fifth-grade class. The field guide is designed to be used by kids on their own.

The field guide begins with the usual generic information on birding: binoculars, bird morphology, field guides, birding clothing. One section seeks to convince youngsters that birding is cool and that they should not be self-conscious about going birding.

The bulk of the book is the description of 200 species of common birds found in eastern North America. A page is devoted to each species. Of course, the amount of text one expects in a typical field guide is reduced in this “for kids” guide. Each page has one or two color photographs and a range map, covering all of North America. A line drawing is provided for each species, showing some interesting behavior. For instance, the drawing of the Hermit Thrush shows the distinctive behavior of these birds in raising the tail rapidly and then slowly letting it fall to a normal position. Each species account has five text sections. Look For provides brief information on the characteristics used to identify the species and Listen For gives a description of the vocalizations. The Remember section is used to emphasize distinctive identification features or behaviors. Find It describes the habitat of each species. Finally, a WOW! section describes a neat feature of a species such as the courtship flight of the Scissor-tailed Flycatcher or 1800-mile non-stop migratory flight of Brant.

[Originally published on May 3, 2008]

For the Birds: Human-caused Bird Extinctions

Tuesday is Earth Day. I hope you will take the time to think about how you can make a difference in the protection and conservation of our planet’s organisms and resources. Go to http://ww2.earthday.net/ to find out about Earth Day activities in your local area.

In the last column, I wrote about sources of bird mortality. Many birds die because of direct human activities (for example, overhunting) or indirect effects of our use of the earth (for example, habitat destruction and pollution). Today, we will consider birds that have been pushed over the brink to extinction because of human activities. This sobering topic should make us all take Earth Day even more seriously. Extinction is forever.

Over the past 500 years, over 140 species of birds become extinct. With the exception of only about a dozen species, these birds were driven to extinction by human activities. Of the roughly 11,000 existing birds species, 1200 are currently in danger of extinction.

The majority of these extinctions occurred on oceanic islands. Many of these islands are small so population sizes are never very high. Many birds on oceanic islands become flightless over time and are therefore not able to escape from human hunters. Finally, birds on oceanic islands with few predators are often fearless in the presence of humans or introduced predators.

The Dodo provides an instructive case study for the extinction of island bird species. This species belongs to the order of birds that includes the pigeons and doves. The Dodo was flightless and most individuals were about three feet tall, weighing more than 40 pounds. They were found only on the island of Mauritius, an island off the coast of Madagascar. Dodos were fruit eaters in the Mauritian forests.

Dodos were certainly extinct by 1681, only 174 years after Europeans first became aware of them. Their demise began with the colonization of Mauritius by Dutch settlers around 1600. Although Dodos would have been easy for humans to kill, journals of Mauritian visitors indicate that the meat of Dodos had an unpleasant flavor and was quite tough. Humans hunted other birds, like the Red Rail, for food. The dramatic decline of the Dodos was rather caused by the cats, pigs and monkeys (Crab-eating Macaques) that the Dutch settlers brought with them. These introduced animals took the eggs or nestlings from the Dodo nests on the ground. By cutting forests and hence reducing Dodo habitat, humans accelerated the extinction of the Dodo.

Mauritius and nearby islands were home for 27 species of birds found uniquely on those islands. Today, 24 of those species are extinct. Such is the footprint of human settlement.

Hawaii is notable for a remarkable suite of birds called Hawaiian honeycreepers, found only in Hawaii. Related to our finches, the honeycreepers have not fared well with human development of the Hawaiian Islands. In the past 200 years, ten of the 31 species have been driven to extinction and several others are endangered.

Understanding the causes of extinctions is sometimes difficult. In New Zealand, 25 species of flightless birds called moas existed until about 300 years ago. We know that Maoris colonized New Zealand about 650 years ago and certainly ate moas and their eggs. However, the New Zealand climate has been changing over the past thousand years, reducing the grasslands the moas favored at the expense of expanding forests. How much of the blame for the extinction of the moas should be pinned on humans? We don’t know for sure.

But bird extinctions don’t happen only on islands. We have lost at least three species of North American birds in the past 200 years. We can clearly point an accusing finger at ourselves for two of these extinctions.

The Passenger Pigeon was once the most abundant bird in North America, migrating in astoundingly large flocks. They were colonial breeders, nesting sometimes in groups of 100,000 birds or more. The pigeons were hunted commercially as a cheap food for slaves and the poor. The pigeon population declined slowly from 1800 until 1870. As a result of more sophisticated capture techniques, the Passenger Pigeon population plummeted over the next 20 years with the last major harvest taken in 1896. These pigeons, once numbering in the billions, were hunted to extinction.

The Carolina Parakeet, the only parrot in eastern North America, went extinct because of deforestation and the killing of birds for use in ladies’ hats and for protection of fruit crops.

We know little about the extinction of the Labrador Duck. In all likelihood, the Eskimo Curlew and Bachman’s Warbler are extinct as well with humans having a significant role in their decline.

[originally published on April 21, 2008]

Birds and Cat Mortality

As Earth Day approaches, I want to focus on the negative impacts that humans are having on our bird populations. Under the auspices of the Migratory Bird Treaty Act, 836 species of native North American birds are protected. Of those species, 78 are on the Endangered Species List and 14 more are listed as Threatened. Another 144 are listed as a Bird of Conservation Concern. Collectively, nearly a quarter of our bird species appear to be declining. The situation is probably even worse than we realize because we have very poor population data on many less common birds that are not currently listed as species of concern.

Some birds perish because of natural causes (for example, weather, predation by birds of prey, mammals or snakes, starvation, disease). But an awful lot of bird mortality can be attributed to human activities.

Without a doubt, the most significant impact humans are having on bird populations (and other flora and fauna as well) stems from habitat destruction or degradation. This habitat alteration has complex effects for migratory birds that require particular habitats for wintering, for stop-overs during migration and for nesting. It is hard to precisely gauge the impacts of habitat destruction on our bird populations. But added to deaths from natural causes, habitat alteration may be pushing some birds over the brink to local or even global extinction.

We have better measures of bird mortality from some human-related sources. Collisions of birds with buildings, mostly from flying into windows, claim nearly a billion birds a year. Collisions with cell phone and television/radio towers are responsible for five to 50 million avian deaths a year. Collisions with high tension power lines results in over 100 million bird deaths annually in the United States. Collisions with cars kill 60 million birds a year.

Over-use of pesticides can result in dramatic localized kills of birds. One recent estimate claimed that 72 million birds each year perish from exposure to pesticides. This estimate is surely low because pesticides may act slowly in a bird, resulting in death at a distance from a pesticide hot spot. Pesticides may cause neurological problems for birds, leading to death from starvation.

Cats are a potent source of mortality for birds. They have had devastating effects on some oceanic islands, leading to the extinction of some birds. In North America, we really do not have a good handle on the magnitude of the effects of cats on our birds. A recent study in Wisconsin demonstrated that domestic cats in the countryside kill 39 million birds in that state each year.

A recent article by Victoria Sims and her colleagues published in the journal Diversity and Distributions addresses the impact of cats on birds in urban areas in Britain. Only about 3% of cats in Britain remain indoors at all times.

Controversy reigns in Britain about the impact of cats on bird populations. One study claimed that cats account for a third of the deaths of local bird populations. On the other hand, skeptics argue that no conclusive studies have been done to demonstrate significant impacts of cat predation other than on oceanic islands.

When conducting a predator-prey study, an ecologist often begins by documenting the relationship between predator numbers and prey numbers. One expects to see a negative relationship: when predators are scare, prey density should be high; when predators are abundant, few prey will be found. In the field, such relationships between a cat predator and prey abundance have been found for lions, tigers and lynx. Domestic cats are a bit more complicated because they get some of their nutrition from the cat food that their owners provide.

In the Sims study, bird population numbers were obtained from Breeding Bird Survey (BBS) squares (each 1 km on a side) chosen randomly from across Britain. They focused their attention on 30 squares within urban areas. Within each of these urban BBS squares, they censused cats by door-to-door or telephone surveys.

The ornithologists found a positive relationship between the number of cats and the numbers of individual birds (the more cats, the more birds). This result suggests that cats are not having a significant predatory effect on birds. However, the authors claim that cats may have a strong impact in all of their study squares. The lowest cat density in a BBS square was 132 cats. One might expect to see higher bird densities in an urban study square with no cats. So, this study has shone some light on the controversy of the importance of cat predation on birds but is far from the last word.

[originally published on April 7, 2008]