Our Friends the Birds - Zoological Society of Milwaukee · 2010-09-13 · Our Friends the Birds...
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10 Our Friends the Birds Richard Brodzeller Jack Bartholmai Turkey Vultures clean up dead animals by eating them. Jack Bartholmai The Ruby-throated Hummingbird pollinates plants. Hawks and owls help to control rodents. Red-tailed Hawk Great Horned Owl USFWS/Beth Jackson BWB-ASF Staff Tennessee Warblers eat insects, which helps to control them. The American Robin eats fruit and disperses the seeds in its droppings. USFWS/Lee Karney Richard Brodzeller Many people enjoy bird-watching. Richard Brodzeller Potawatomi Tribe elders took part in a 2007 naming ceremony for this Bald Eagle at the Milwaukee County Zoo. Why Are Birds Important? Why should you help birds? Here are 10 ways birds help you by playing an important role in your lives and your environment. 1. Birds control insect populations They eat insects and caterpillars that can damage crops, gardens, forests and natural areas. 2. Birds control pests Hawks and owls feed on mice, rats and other rodents, which helps to control the numbers of these pests. 3. Birds disperse seeds Seeds spread by bird droppings allow new trees and other plants to grow without people having to plant them. 4. Birds pollinate plants Nectar-drinking birds like hummingbirds pollinate plants as they visit flowers seeking nectar. Plants, crops, and trees wouldn’t grow without birds and insects to pollinate them. 5. Birds belong to the food chain Birds and their eggs provide food for predators, including other birds, mammals, reptiles, amphibians, fish and humans. 6. Birds clean up dead animals Vultures and some hawks eat roadkill and dead livestock. If birds did not eat dead animals, these would last (and smell bad!) for a long time. 7. Birds offer enjoyment Many people enjoy bird-watching and listening to bird songs. Since birds are widespread, they can be enjoyed almost anywhere, including backyards, parks, nature centers, natural areas and wildlife refuges. 8. Birds make avi-tourism possible and contribute to the economy Bird-watching is a popular form of recreation. In 2006, Americans spent $31 billion on equipment, lodging, travel and other costs while watching birds (USFWS 2006, 2008). So, birds make an important contribution to the economy. 9. Birds have cultural significance Feathers may be used in some Maya, Inca, Aztec and North American Indian ceremonies. In the past, people observed bird migration to help them determine appropriate times to plant and harvest crops. 10. Birds help monitor the environment Birds are sensitive to disturbances in the environment. Therefore, by observing bird behavior and comparing numbers of each bird species from year to year, humans can monitor the health of the environment. [The decline of the Peregrine Falcon in the U.S. led to the discovery of dangerous levels of the insecticide DDT in their food source. DDT caused thinning of eggshells so that the eggs broke and most young birds did not develop or hatch. DDT, once thought of as beneficial for its ability to control mosquito populations and the spread of malaria, is now recognized as a bio-accumulative toxic chemical in the environment. It is banned in the U.S.]
Transcript of Our Friends the Birds - Zoological Society of Milwaukee · 2010-09-13 · Our Friends the Birds...
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Our Friends the Birds
Richard BrodzellerJack Bartholmai
Turkey Vultures clean up dead animalsby eating them.
Jack Bartholmai
The Ruby-throated Hummingbird pollinates plants.Hawks and owls help to control rodents.
Red-tailed Hawk Great Horned Owl
USFWS/Beth Jackson
BWB-ASF Staff
Tennessee Warblers eat insects, whichhelps to control them.
The American Robin eats fruit and disperses the seeds in its droppings.
USFWS/Lee Karney Richard Brodzeller
Many people enjoy bird-watching.
Richard Brodzeller
Potawatomi Tribe elders took part in a2007 naming ceremony for this Bald Eagle
at the Milwaukee County Zoo.
Why Are Birds Important?
Why should you help birds? Here are 10 ways birds helpyou by playing an important role in your lives and yourenvironment.
1. Birds control insect populationsThey eat insects and caterpillars that can damage crops,gardens, forests and natural areas.
2. Birds control pestsHawks and owls feed on mice, rats and other rodents,which helps to control the numbers of these pests.
3. Birds disperse seedsSeeds spread by bird droppings allow new trees and other plants to grow without people having to plant them.
4. Birds pollinate plantsNectar-drinking birds like hummingbirds pollinateplants as they visit flowers seeking nectar. Plants, crops,and trees wouldn’t grow without birds and insects to pollinate them.
5. Birds belong to the food chainBirds and their eggs provide food for predators, including other birds, mammals, reptiles, amphibians,fish and humans.
6. Birds clean up dead animalsVultures and some hawks eat roadkill and dead livestock. If birds did not eat dead animals, these would last (and smell bad!) for a long time.
7. Birds offer enjoymentMany people enjoy bird-watching and listening to birdsongs. Since birds are widespread, they can be enjoyedalmost anywhere, including backyards, parks, nature centers, natural areas and wildlife refuges.
8. Birds make avi-tourism possible and contribute to the economyBird-watching is a popular form of recreation. In 2006,Americans spent $31 billion on equipment, lodging,travel and other costs while watching birds (USFWS2006, 2008). So, birds make an important contributionto the economy.
9. Birds have cultural significanceFeathers may be used in some Maya, Inca, Aztec and North American Indian ceremonies. In the past,people observed bird migration to help them determineappropriate times to plant and harvest crops.
10. Birds help monitor the environmentBirds are sensitive to disturbances in the environment.Therefore, by observing bird behavior and comparingnumbers of each bird species from year to year, humanscan monitor the health of the environment. [The declineof the Peregrine Falcon in the U.S. led to the discovery of dangerous levels of the insecticide DDT in their foodsource. DDT caused thinning of eggshells so that theeggs broke and most young birds did not develop orhatch. DDT, once thought of as beneficial for its ability tocontrol mosquito populations and the spread of malaria,is now recognized as a bio-accumulative toxic chemicalin the environment. It is banned in the U.S.]
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GUESS WHAT?With a tailwind, it took this bird15 hours to fly 500 miles non-stopacross the Gulf of Mexico!
AMAZING BIRD STORY!December 2001: Tropical Education Center of the Belize Zoo Staff from the Zoological Society of Milwaukee’s Birds WithoutBorders–Aves Sin Fronteras® project band and release an ovenbird.August 2003: Ontario, Canada Bird researchers capture the same ovenbird! That means that this little bird flew almost 2,000 miles twice each year!
We think this is very cool. WHY?Billions of migratory birds fly similar distances twice each year between their breeding and wintering grounds.Fewer than 1 in 1,000 songbirds are ever recovered!
The Miracle of Migration
Amazing Bird StoryThis is the story of a little bird that flew at least 7,600miles. This tiny Ovenbird weighed only about 2/3 of anounce – about as much as eight pennies! The fact that such a small creature flew thousands of miles each year to migrate seems nothing short of miraculous. But how do we know this bird really flew that far? Let us tell you.
Our Birds Without Borders – Aves Sin Fronteras® staff have been banding birds in Wisconsin since 1997 and inBelize since 1999. When we band birds, we capture them inspecial nets called mist nets, carefully remove them, placea numbered U.S. Bird Banding Laboratory aluminum bandon their leg, examine them, take measurements, and thenrelease the birds. (See Appendix 3 for more information on bird banding.) Bird banding requires very specializedtraining and a permit from the U.S. (and Belize) govern-ments. Banding does not harm the birds in any way andprovides valuable information on the birds captured.
From 1997 through 2007, we banded 9,867 birds at ourWisconsin study sites and 4,752 birds at our Belize studysites. Sometimes we recaptured birds that we had banded,either later that same year or in following years. Althoughit is rare, researchers occasionally capture birds that werebanded by other bird banders. Fewer than 1% of non-gamebirds (songbirds, hawks, owls, wading birds and otherbirds not eaten as game) banded are ever recaptured inareas other than where they were originally banded.Recaptures provide valuable information on little-knownmigration routes and on how long birds live. Of more than14,000 birds we banded in Wisconsin and Belize, only 15have been recovered by others (recaptured or found dead).BWB-ASF staff recaptured four birds banded by other ban-ders. (For information on recaptures at our Wisconsinstudy sites please see pages 53 and 72.)
Our most exciting recovery by another bird bander was the recapture of a little Ovenbird. This bird originally was banded by BWB-ASF staff in Belize and recaptured in Ontario, Canada! It had made the more than 1,900-miletrip between Belize and Canada at least four times, which isamazing considering the bird’s size. We know that becauseit was recaptured two years after we had banded it. Thatmeant that it had to have made the trip twice a year for two years: a total of 7,600 miles.
The recaptures of Neotropical migrants such as thisOvenbird always leave us in awe, as these birds make twolong-distance migrations (more than 1,500 miles one way)every year. They spend northern winters in southern
Mexico, the islands in the Caribbean Sea, or Central andSouth America. In spring, they migrate to North America to breed and raise young during our summers. In fall,they migrate south again.
So, when you see a migrant in spring, think about how far it flew just to reach Wisconsin! Migrants will makeanother long journey south to the tropics in fall. If theysurvive, many return to exactly the same place the follow-ing year to breed and raise young. When you preservehabitats, birds can come back to breed in the same areaand find a place that is familiar to them. By providinghabitat for birds during migration, you can increase thebirds’ chance of survival during their long journeys.
Why and How Birds Migrate
(Note for scientists: Information for this section was adapted from Gill 1990, Elphick 1995, Able 1999, andDeinlein 2001.)
What Is Bird Migration?Migration is the seasonal movement of birds at predictable times of the year, generally between breeding and non-breeding areas.
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Why Do Birds Migrate?Many people think that birds migrate because of coldnorthern winters, but the main reason is food. Thechange of seasons causes a decrease in food supply.Birds then fly to an area with more food.
Another reason for migration is reproduction. Birdsmigrate to a specific area to breed and raise theiryoung. During the North American summer and fall,food is very plentiful, which benefits breeding birdsand their chicks.
Which Birds Migrate?Many (62%-80%) birds that breed in North Americamigrate south in fall and return in spring.
Neotropical migrants are birds that migrate in the fall(August-October) and spend the non-breeding season in areas south of the Tropic of Cancer (southern Mexico,Central and South America, and the Lesser and GreaterAntilles in the Caribbean Sea). Please see page 20 for amap showing the Tropic of Cancer. A more correct termthat is now used is Nearctic migrants, since these birdsspend more time in the tropics (up to six months) than ontheir North American breeding grounds. Many Neotropicalmigrants are insectivores; they eat mainly insects, andthey do not visit backyard bird feeders. Neotropicalmigrants remain in the tropics until April, and thenmigrate back to breed and raise young in North America,where there are plenty of insects. Familiar Neotropicalmigrants include Baltimore Orioles, warblers such asMagnolia Warblers and Ovenbirds, and thrushes such as Wood and Swainson’s Thrushes. The Rose-breastedGrosbeak is one Neotropical migrant that can beobserved at bird feeders.
Short-distance (temperate) migrants such as American Robins and Red-winged Blackbirds spend the non-breeding season north of the Tropic of Cancer. These areas include the U.S., northern Mexico and thenorthern Bahamas. They migrate only as far as they needto find food. Short-distance migrants eat insects, butmany also can eat seeds and fruits. These migrants begin to return to Wisconsin in March and April.
Resident birds do not migrate. They can find food year-round, even during North American winters! FamiliarWisconsin resident birds include the Black-cappedChickadee and Downy Woodpecker.
Lynn Miller
Richard Brodzeller
Baltimore Oriole
Richard Brodzeller
Wood Thrush
Magnolia Warbler
Ovenbird
Vicki Piaskowski
Jack Bartholmai
Swainson’s Thrush Rose-breasted Grosbeaks eat seeds andcan be observed at bird feeders.
Heather Neldner
USFWS/Lee Karney
American Robin Red-winged Blackbird
USFWS/Donna Dewhurst
Neotropical migrants
Short-distance (temperate) migrants
USFWS/Donna Dewhurst
Black-capped Chickadee Downy Woodpecker
USFWS/Donna Dewhurst
Residents
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How Do Birds Prepare for Migration?To prepare for migration, birds become hyperphagic;that is, they eat more food,which is then stored asfat. Fat is the fuel used fortheir long journey. Fat is normally about 3%-5% of the bird’sweight. Some migrantscan deposit up to 30%-50% of their body weightin fat before migration. Forexample, a Wood Thrushwith low fat stores normally weighs about 41-51 grams(1.5-1.8 ounces). To prepare for migration, it depositsfat and can weigh up to 63 grams (2.2 ounces), orabout 25% more. The Ruby-throated Hummingbirdweighs only 5 grams (.2 ounce) and can use stored fatto fuel a non-stop, 24-hour flight across a 600-milestretch of open water from the U.S. Gulf Coast toMexico’s Yucatan Peninsula!
When Do Birds Migrate?Day Migrators:
Many soaring birds, such as hawks, migrate by day.Hawks travel inland by flying and catching thermalsthat occur only over land.(Thermal updrafts are ris-ing columns of warm airthat spiral upward and liftbirds up so they can flywithout flapping, savingenergy. Hawks also usethermals when they arenot migrating.) Hawks andother raptors do not like tomigrate over water. When they reach Mexico andCentral America, the land narrows and the hawks arefunneled over this land bridge. This causes huge con-centrations of raptors, sometimes as many as 100,000passing in one day.
Insectivores, such as swifts and swallows, also fly during the day, feeding on insects as they fly.
Flocking birds, such as waterfowl and some finches,will fly during the day.
Jack Bartholmai
Ruby-throated Hummingbird
© B.K. Wheeler/VIREO
Broad-winged Hawk
© R. Curtis/VIREO
Chimney Swift Tree Swallow
Jack Bartholmai
USFWS/John & Karen Hollingsworth
Blue-winged Teal Bufflehead
USFWS/Donna Dewhurst
Night Migrators:Most songbirds (passerines) travel during the night.They spend the daylight hours resting and searchingfor food in the unfamiliar places where they stop torest. Songbirds cannot soar like hawks, but must flaptheir wings the entire time they fly, which generates a lot of heat. Temperatures are lower at night and theair is stiller, which make better flying conditions for songbirds.
USFWS/Donna Dewhurst
Wilson’s Warbler
USFWS/Donna Dewhurst
Ruby-crowned Kinglet Blue-winged Warbler
BWB-ASF Staff
How Fast Do Birds Fly?In still air, most songbirds fly at 20-30 mph. Waterfowl and shorebirds can fly at 30-50 mph. A tailwind allows the bird to fly faster.
How Do Birds Navigate?Birds have excellent vision and rely on visual land-marks for local and long-distance migration. They use key land features such as mountains, rivers, coastsor even large buildings. There also are three types of“compasses” a bird uses to find its way. Birds can usethe sun, the stars and the Earth’s magnetic field.
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1. Birds use the sun as acompass. They use thepositions of the sunduring the day to navi-gate. They also can usethe setting sun as anindication of due west.
2. Night flyers use celestialnavigation, which meansthey find their way byknowing the patternsof the stars in the sky,and by knowing specialstars like the NorthStar. In their first yearof life, birds memorizethe position of the con-stellations in relationto the North Star. Thesestar patterns stay thesame even though the Earth moves through space,making the constellations appear to move to different spots in the sky during the year.
3. Birds have tiny grains of a mineral called magnetitejust above their nos-trils. This mineral mayhelp them to navigateusing the Earth’s magnetic field, which tells the bird thedirection of true north.Birds seem to be muchmore sensitive thanhumans in their ability to sense the Earth’s magnetic field. (The Earth has a weak magneticfield. It acts like a huge bar magnet. A compassuses this magnetic field, and this is what causes a compass to point north.)
Petrels and pigeons can use their sense of smell to find their way, but it supplements the above-mentioned cues.
How Do We Learn About Migration?Scientists throughout the world conduct many typesof research to learn about migration. Heavy concen-trations of migrating birds can be seen on weatherradar screens. Many bird observatories and bird organizations conduct migration counts and bandbirds to learn about the numbers and species of
USFWS/Lee Karney
By studying European Starlings, scientists learned that birds can orient
by the sun’s position in the sky.
USFWS/Dave Menke
Scientists studied Indigo Buntings inplanetariums and learned that birds
can use the stars to navigate.
USFWS/Lee Karney
In research on homing pigeons (RockPigeons), scientists determined thatthey are sensitive to magnetic fields.
birds that migrate each year. Researchers also use flight calls of birds as they fly over at night to study which songbirds are migrating.
BWB-ASF Bird banding research (1997 photo)
Richard Brodzeller
Bird banding research has allowed scientists to learnabout migration. (Please see Appendix 3 to learn moreabout bird banding.) Many birds are banded and some-times those birds are caught again, or found afterthey die. By checking the band number and reportingit to the Bird Banding Laboratory, scientists can learnwhere the bird was first banded and how far it traveled.In this manual, we discuss some of the BWB-ASF birdbanding research results.
The Importance of Migration Stopover SitesMost songbirds don’t fly straight through to their destination, but stop a number of times to rest and feedduring migration. The places they stop are called stopoversites, or staging areas. Birds remain at stopover sites forvarying amounts of time based on the weather and howmuch fat they have stored. Some birds stop only one dayto rest and feed and then continue their migration. Others will remain at stopover areas for weeks.
Most Neotropical and short-distance migrants stop alongthe way to rest and feed.
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This is where private landowners can be of particular help to migrating birds. Scientists used to think that birdsneeded big plots of land to stop at during migration. Butwe have been finding that even small areas, like backyards,can be important spots to help migrating birds. Those smallareas must have the right kinds of plants, shelter and foodfor birds, however. For more information, see the next sections on what birds eat. Also see the chapter on whatyou can do to help birds on pages 22-38. For detailed information on migration stopovers, please see Appendices 6 and 7.
What Do Birds Eat During Migration?Adaptations for a Bird’s Diet
Birds are amazingly diverse, and the way that they feed depends on how they move, their bill (beak)structure, and their digestive system. The bird’s bill is its key adaptation for feeding; its size, shape andstrength greatly affect the bird’s diet. In these photos,you can see different ways that birds’ bills are adaptedto the foods they eat.
USFWS/Beth Jackson
The Red-tailed Hawk has a bill adapted for tearing meat.
USFWS/National Wildlife Federation USFWS/Gary Kramer
The Common Loon’s bill is adapted for catching fish.
Great Blue Herons have a bill adaptedfor catching prey while wading.
USFWS/Lee Karney BWB-ASF Staff
The Song Sparrow’s bill allows it to eat hard seeds as well as insects.
The Tennessee Warbler feeds mainly on insects, but may add fruit to its
diet during fall migration.
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Butterfly and moth caterpillars (larvae of Lepidoptera)
Sawflies (Hymenoptera) Sawfly caterpillars (larvae of Hymenoptera)
Spiders (Araneae)
Leafhoppers, cicadas and aphids (Homoptera)
Flies (Diptera)
BWB-ASF research focused mainly on the diets of smallsongbirds; so we will concentrate our discussion on songbird studies.
What Birds Eat During Spring MigrationDuring spring migration songbirds eat mainly arthro-pods (spiders and insects). Birds eat flying insectsand/or find insects and spiders in the developingleaves and flowers of trees and shrubs.
Pictured here are some examples of insects and spidersthat songbirds eat to fuel their migratory journeys.
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Birds also feed on bees, wasps and ants (Hymenoptera),beetles (Coleoptera) and true bugs (Hemiptera).
Birds time their spring migration so that they arrivewhen insects are available. But sometimes birds mustdeal with harsh weather and may arrive before plantsdevelop leaves where insects hide. To compensate,
birds may move to shore-lines to feed on flyingaquatic (water-associated)insects. Midges (a type offly) and emerging aquaticinsects can be a very impor-tant early source of food forbirds near lakes, coastalmarshes and wetlands(Ewert and Hamas 1996,Smith et al. 2004, Ewert et al. 2006).
What You Can Feed Birds during Spring MigrationWatching bird behavior in spring either with or with-out binoculars will allow you to see birds pluckinginsects and spiders from developing leaves, buds and
flowers. You also can see birdsflying into the air to captureairborne insects. Althoughmost food for birds duringmigration is found on plants,a few species of birds do eatfoods provided by humans.Rose-breasted Grosbeaks,White-throated and White-crowned Sparrows are some
of the birds that also will feed on seeds during springmigration. These birds eat plant seeds, but also willfeed at bird feeders.
Special feeders are avail-able to provide sugarwater to hummingbirds.Baltimore Orioles feedmainly on insects; how-ever, they will also eatoranges as well as sugarwater in hummingbirdfeeders. Nectar feedersdeveloped especially for orioles are now available.Gray Catbirds, Cape May and other species of warblershave also been observed feeding on oranges duringspring migration.
Marcia T. Sinner
Midges are an important food for birdsearly in the spring.
Heather Neldner
BWB-ASF Staff
Rose-breasted Grosbeak
White-throated Sparrow
Vicki Piaskowski
Red-osier dogwood
K. Kanoti, Maine FS, Bugwood.org
Black cherryT. Webster, USDA-ARS, Bugwood.org
Common elderberry
C. Evans, River to River CWMA, Bugwood.org
Blackberry
USFWS/Donna Dewhurst Richard Brodzeller
White-crowned Sparrow Baltimore Oriole feeding on an orange.
BWB-ASF Staff USFWS/Steve Maslowski
Gray Catbird Cape May Warbler
What Birds Eat During Fall MigrationDuring fall migration birds supplement their insectand spider diet with a variety of fruits (berries) thatgrow on both native and non-native plants. (Nativeplants are those found naturally and historically in an area.)
The type of fruit that birds can eat depends on theirbill size and shape, what is available during theirmigration period, and where they stop to rest andfeed. Larger birds such as American Robins and GrayCatbirds can eat whole fruits. Smaller birds like war-blers pierce the fruit with their bill to drink the juices and pulp.
These photos show some of the native Wisconsin fruitsthat birds eat during migration.
P. Wray, Iowa St. Univ., Bugwood.org
Eastern red cedar
T. Bodner, S. Weed Science Soc., Bugwood.org
Summer grape
BWB-ASF Staff
Gray Catbirds feed on many types of fruits.
BWB-ASF Staff
Bay-breasted Warblers pierce fruit withtheir bills and drink the pulp and juice.
USFWS/Donna Dewhurst
Black-capped Chickadee
USFWS/James Leupold
American Robin
USFWS/Steve Hillebrand
Bald Eagle
Jack Bartholmai
Pileated Woodpecker
J. H. Miller, USDA-FS, Bugwood.org
Virginia creeper
USFWS/Lee Karney
American Robins feed on many types of fruits.
Bringing up Baby – What Birds Need
During the Breeding Season
What Do Breeding Birds Need?Once birds have migrated back north, they and thosespecies that are residents start looking for places tobreed. This is another time when private landownerscan manage their land to help birds. During the breeding season birds need:
• an area that contains a safe place to build a nest• food for both the adult birds and their offspring.
Different bird species need different size areas for nest-ing. Some bird species areconsidered area-sensitive, and they are more likely to be found in large areas of suitable habitat. Examples ofarea-sensitive birds in easternforests include the Black-throated Blue Warbler and the Black-and-white Warbler.
Examples of area-sensitive birds in grasslands include the Northern Harrier and Upland Sandpiper.
The nesting area is oftencalled a breeding territory, an area that the male, andsometimes the female, defendfrom other birds of the samespecies. Because birds estab-lish breeding territories dur-ing the spring and summer,they are less likely to be seenin yards and at feeders at thistime. The following sectionsgive more specifics, and theyalso include, for scientists and researchers, referencesin parentheses of other scien-tists’ reports. We list the references in order to give the researcher who first dis-covered this informationcredit for their work.
USFWS/Steve Maslowski
Black-throated Blue Warbler
Vicki Piaskowski
Black-and-white Warbler
Kevin Bronson
Northern Harrier chicks
The size of a bird’s breeding territory varies dependingon the location and quality of the habitat. Black-cappedChickadees have breeding territories that range from3.6 to 17.9 acres (Smith 1991). The American Robindefends only its nesting site and feeds with otherrobins up to 300 meters (984 feet) from its nest(Sallabanks and James 1999). Bald Eagles can have a breeding season territory size ranging from 250 to1,000 acres (Buehler 2000). Pileated Woodpeckersdefend their territories not only during the breedingseason, but also year-round, and their territory sizeranges from 132 to 1,190 acres (Bull and Jackson 1995).
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A good nesting area shouldhave food for both the adultsand young. Most birds breedand raise young during thetime when food is most abun-dant. During North Americansummers, arthropods (insectsand spiders) are plentiful.Throughout the breeding season birds need a high-
protein diet. So birds that usually eat nectar, fruits andseeds switch to a diet containing a lot of protein, which is provided by spiders and insects (Ehrlich et al. 1988).This switch in diet is another reason why birds are seen at bird feeders less in the summer than at other times of year. Native plants and undisturbed habitats are espe-cially rich sources of insect and spider foods for birds. (For more information on plants that provide insect food for birds please see pages 55-57.)
USFWS/P. Reynolds
Nashville Warbler
USFWS/Dave Menke
Eastern Bluebird
Jane Hartwig
Magnolia Warbler nestlings
Problems That BirdsEncounter During theBreeding Season
Nest PredatorsMany mammals and somebirds eat eggs and/ornestlings (young birds innests). This is called nestpredation. In the past, it was not always possible todetermine which animalpreyed on a nest. Now,motion-activated camerasand miniature video cam-eras allow researchers todetermine some of the ani-mals that do feed on eggs and nestlings. This new tech-nology has revealed that there are many more differentkinds of nest predators than originally thought.
Nest predators that have been documented feeding on eggs or nestlings in forested areas include fishers,snakes, flying squirrels, mice, black bears, hawks,Barred Owls, Eastern chipmunks, red and gray
squirrels, raccoons, Blue Jays, red-backed voles,striped skunks, Gray Jays, and American Crows(Strickland and Ouellet 1993, Fenske-Crawford andNiemi 1997, Williams and Wood 2002, Weatherheadand Blouin-Demers 2004).
Predators that have been documented in grasslandsfeeding on eggs or nestlings include raccoons, 13-lined ground squirrels, snakes, American badgers,domestic cats, hawks, foxes, coyotes and dogs,striped skunks, opossum, mice, white-tailed deer,weasels, and Northern Harriers (Pietz and Granfors2000, Renfrew and Ribic2003). A recent study inWisconsin videotaped cattle removing nestlingsand eggs from grasslandnests, but it was notknown if the cattle ate them (Nack and Ribic 2005).
Richard Brodzeller
Eastern gray squirrel
Stock Photography
Eastern chipmunkM. Mengak, UGA, Bugwood.org
Red squirrel
Richard Bautz
13-lined ground squirrel
D. Cappaert, MSU, Bugwood.org
Deer mouseStock Photography
American Crow
USFWS/Dave Menke
RaccoonD. Cappaert, MSU, Bugwood.org
Garter snake
Stock Photography
Striped skunk
Stock Photography
Black bear
Richard Brodzeller
Blue Jay
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Native Plants Provide a Safe Place to NestResearch has shown that nests built in Amur andTartarian honeysuckle and common buckthorn (non-native shrubs) had higher rates of nest predationthan nests built in native shrubs such as hawthorn,viburnum or spicebush (Schmidt and Whelan 1999,Borgmann and Rodewald 2004). Researchers foundthat nests in non-native plants were built lower thanthose in native plants, which could make them easierfor nest predators to reach. They also found that nestsbuilt in native plants were supported by more and larger branches, which could make it difficult for apredator to access the nest. Native plants like haw-thorns have thorns, which may discourage predatorsfrom trying to reach the nest. Native plants not onlyprovide birds with a safer place to nest, but they also provide better and more food for birds.
Nest ParasitismThe Brown-headedCowbird is a nest or broodparasite, meaning that itlays its eggs in the nests ofother bird species andallows these birds to raiseits young. Brown-headedCowbirds were originallyfound in the western U.S.,where they followed herds of buffalo and fed on theinsects stirred up by their movement. Because the buffalo (and the cowbird’s food source) continued tomove, the cowbird could not stay in one place to builda nest and raise its young. So it developed a strategyof laying its eggs in the nests of other birds that thenraise the cowbird young.
Changes in the landscape such as clearing forestedareas, building roads, and using large areas of land foragriculture have allowed the cowbird to spread widelyso that it is now found throughout the U.S. and partsof Canada and Mexico. Brown-headed Cowbirds havebeen documented laying their eggs in the nests of 220different bird species, and 144 of these have actuallyraised the cowbird young (Lowther 1993).
Some bird species have developed strategies to avoidraising cowbird young; they will eject cowbird eggsfrom their nest or build a new nest on top of the cow-bird eggs. Birds that raise cowbird young are called“host species.” Raising cowbirds can decrease thenumber of the host young that survive. Young cow-birds tend to hatch earlier, develop more quickly andare larger than most songbirds; as a result, they mayget fed more often or push the host young out of thenest. Nest parasitism by Brown-headed Cowbirds candramatically decrease the number of host young thatare raised, and this is believed to be one factor causing population declines in some songbirds.
Habitat FragmentationHabitat fragmentation is the breaking up of one large,intact area such as a forest, grassland,or wetland intosmaller pieces.Instead of one largehabitat, fragmentedhabitats are oftenseparated by roads,housing, commer-cial development or farmland. Whena habitat is broken
up into smaller pieces, instead of one large habitatwith a large core area, the fragments have many edgesor areas in which the interior can be easily accessed.Fragments allow Brown-headed Cowbirds to enter andparasitize bird nests and also provide access routes fornest predators. Many birds do not reproduce success-fully in fragmented habitats, due to Brown-headedCowbird nest parasitism and increased nest predation.
One study showed that forest fragmentation also canreduce the insect food available to birds that search for food on the ground, such as the Ovenbird (Burke and Nol 1998). Small forest fragments had more bareground and fewer seedlings, shrubs and dead leaves,which may explain why there was less insect food for birds in these areas.
Vicki Piaskowski
Common buckthorn
Vicki Piaskowski
Tartarian honeysuckleR. Webb, Bugwood.org
Blackhaw viburnum
R. Webb, Bugwood.org
Downy hawthorn
J. D. Ward, USDA-FS, Bugwood.org
Fragmented habitat
Jack Bartholmai
Brown-headed Cowbird
Classifying Wisconsin’s Birds
There have been more than 429 bird species recorded inWisconsin. Of these, 343 are species you’re likely to see ona regular or at least occasional basis (Mueller 2008).
These birds are classified by the amount of time they spendin Wisconsin during their lifespan. This is also termed sea-sonality. Because many birds leave North America to spendwinters in areas that provide them with enough food tosurvive, birds are classified by where they spend the NorthAmerican winter. (For birds found in Wisconsin, the NorthAmerican winter is generally referred to as the “non-breeding” season.) Birds in Wisconsin belong to severalgroups, and sometimes combinations of those groups.Following are explanations of the different Wisconsin sea-sonality classifications (Rappole 1995, AOU 1998-2007)and the abbreviations used in this manual:
(R): Resident birds are present in Wisconsin year-round.They do not migrate.
(S): Short-distance (temperate) migrants spend the non-breeding season north of the Tropic of Cancer, in the U.S.,northern Mexico, and the northern Bahamas.
(R/S): Resident/Short-distance migrants have some individuals that are present in Wisconsin year-round
and others that spend the non-breeding season in the U.S. and northern Mexico.
(N): Neotropical migrants breed north of the Tropic of Cancer (mainly in North America), but spend the non-breeding season south of the Tropic of Cancer insouthern Mexico, Central America (including Belize),South America and the islands in the Caribbean Sea(Greater and Lesser Antilles). They can be found in thesenon-breeding areas for up to six months each year.
(S/N): Short-distance/Neotropical migrants have someindividuals that spend the non-breeding season in theU.S. and northern Mexico and others that can be foundsouth of the Tropic of Cancer.
There are 226 species of birds that breed in Wisconsin(Cutright et al. 2006). In the table found on pages 45-49, we note the bird species that breed in Wisconsin that we found at the BWB-ASF study sites.
Terms Used to Describe Habitats that
Birds Use
In this manual, we use a number of standard terms todescribe bird habitats. Following are definitions of someof those terms. Please see Appendix 10 for the scientificnames of plants listed in this manual.
Tropic of Cancerat 23.5˚ N latitude
Many birds that breed in North America leave in the fall and migrate to their non-breedinghomes. Neotropical migrants travel to areas south of the Tropic of Cancer
Vicki Piaskowski
Mat of sphagnum moss and bog plants
Larry Hopwood
Coniferous forest
20
Bog: A special type ofwetland that supportsa unique group oftrees, shrubs and forbsthat grow on a mat ofsphagnum moss.
Coniferous area or forest: One dominated by evergreen trees thathave cones.
21
Forb: Non-grass herbsthat include wildflowers.
Vicki Piaskowski
Wild bergamot
Vicki Piaskowski
Grassland
Vicki Piaskowski
Shrub-carr marsh area
Kari Williams
Wetland
Kari Williams
Deciduous forest
Deciduous area or forest: One dominated by plantsthat lose their leaves. InWisconsin, this happensin fall or early winter.
Wetland: An area filledor saturated with waterthat supports vegetationadapted to growing inwet conditions. Wetlandsinclude swamps, marsh-es, bogs, wet and sedgemeadows, wet prairiesand fens (areas of low,flat, marshy land).
Shrub-carr marsh: A wetland plant community with tall, deciduous shrubs.
Graminoid: Grass-likeplants that include grasses, sedges and rushes.
Grassland: An area dominated by grasses.
Forest: An area covered with trees andunderbrush. The canopy is the upper-most layer of the forest, and canopytrees have tops that are exposed to fullsunlight. The understory consists ofthe layers that grow under the canopy.
Sedge meadow: A type of wetland dominated by sedges.
