CAL IFORNIA NATURAL H ISTORY GUIDES

F IELD GUIDE TOOWLS OF CAL IFORNIA

AND THE WEST

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Ca l i f o rn ia Natu ra l H i s to r y Gu idesPhyllis M. Faber and Bruce M. Pavlik, General Editors

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Field Guide to

OWLS of California and the West

Hans Peeters

Illustrations and photos by Hans Peeters

U N I V E R S I T Y O F C A L I F O R N I A P R E S S

Be rke l e y L o s Ange l e s L ondon

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The publisher gratefully acknowledges the generous

contributions to this book provided by

the Gordon and Betty Moore Fund

in Environmental Studies

and

the General Endowment Fund of the

University of California Press Foundation.

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vi

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CONTENTS

Preface xi

INTRODUCTION 1

What Is an Owl? 2

Owls in California and the West 5

AN OWLS BODY 11

An Owls Head 12

Senses 17Vision 17

Hearing 23

Touch 25

Voice 26

Skeleton and Legs 28

Wings 32

Feathers 35Silent Flight 35

Thermoregulation 38

Plumage 39

Hygiene 41

Parasites 46

Deconstructing a Mouse 46Digestive System 46

Pellet Analysis 49

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AN OWLS LIFE 53

Predators and Predator Avoidance 54Predators of Owls 54

Going Undetected 56

Mobbing 59

Defensive Behavior 63

Hunting and Eating 65Feeding 69

Owl Foods 71

Owl Ecology 72

Reproduction 79Territoriality 79

Pair Formation and Courtship 80

Nests and Eggs 83

Young and Their Care 87

Dispersal and Migration 91

FINDING AND WATCHING OWLS 95

Finding Owls 96When to Look for Owls 96

Where to Look for Owls 97

Direct Evidence: Songs, Calls, and Deceptions 100

Circumstantial Evidence 104

Finding Owl Nests 112

Watching Owls 115Owl Photography 117

Owl Identification 118

OWLS AND HUMANS 123

Attitudes Past and Present 124Native Californians and Owls 126

Owls in the Modern World 128

The Barn Owl Industries 130

Owl Conservation 134Owls in Trouble 134

Hazards to All Owls 144

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Living with Owls 148Nest Boxes 149

Wildlife Rehabilitation 153

SPECIES ACCOUNTS 157

Overview 158Identification Key 159

Range Maps 161

Barn Owl 162

Flammulated Owl 169

Western Screech-Owl 174

Eastern Screech-Owl 180

Whiskered Screech-Owl 184

Great Horned Owl 188

Snowy Owl 195

Northern Hawk Owl 200

Northern Pygmy-Owl 204

Ferruginous Pygmy-Owl 213

Elf Owl 217

Burrowing Owl 221

Spotted Owl 229

Barred Owl 235

Great Gray Owl 240

Long-eared Owl 247

Short-eared Owl 253

Boreal Owl 261

Northern Saw-whet Owl 265

Glossary 275

References 281

Index 305

Additional Captions 324

Plates follow page 194

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PREFACE

Soft, mellow hoots drift from a stand of trees down the block onthis bright April morning. Is that an owl? your child asks. Doyou know the answer?

Because of the secretive and chiey nocturnal habits of owls,many people, although they can recognize one, have never seenan owl in the wild. Most urban humans are unaware that owlsmay live in their midst, going about their business in the darkafter we have turned on the lights that so eectively shut o con-tact with the natural world.

No, the calling bird was not an owl. It was a male MourningDove (Zenaida macroura) with romance on his mind. Owls rarelycall by day, particularly when it is sunny. But had you listenedafter nightfall, you might have heard the trill of a WesternScreech-Owl (Megascops kennicottii) coming from those verysame trees, or the disembodied rasp of a Barn Owl (Tyto alba)somewhere in the star-laced sky.

The purpose of this book is to acquaint the reader with agroup of birds that are often regarded as enigmas even by thosewho do see them occasionally. Besides providing informationhelpful in identifying the various species, the book includes sug-gestions as to how to nd these private creatures, details abouttheir feathers and body structure (with special emphasis on theirextraordinary senses of sight and hearing), and much more.

My intent is to present a selection of facts (and anecdotes)about owls that will heighten the understanding of these singularbirds and enhance the pleasure of learning about them andwatching them. Although it obviously is not the purpose of thisguide to serve as an encyclopedic scientic reference, this book isalso aimed at professional biologists, who will nd useful infor-mation they may not have previously known. In discussions of

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topics not deemed common knowledge, free use has been madeof the available scientic literature, complete with selectively cho-sen citations, so that the interested reader can pursue a given topicto learn more detail. Here and there I have included my own ob-servations and occasionally bold speculations without citation.Some species of owls are well studied, but there are large gaps inour knowledge about others. For example, little is yet knownabout some of the details of breeding in pygmy-owls (Glaucid-ium), which are most commonly seen during the nonbreedingseason. Perhaps some readers will be inspired to go in search ofthese elusive gnomesthey are more numerous than is generallybelieved.

My original plan was to write a volume about owls as a com-panion to my field guide on diurnal birds of prey, Raptors of Cal-ifornia (Peeters and Peeters 2005). Once my editors realized, how-ever, that the number of owl species found in California was onlya few shy of the total number of species found in North America,they suggested I venture beyond Californias borders, and so thetext expanded, funguslike, into the other western states. Althoughthere is clearly a California focusnot surprisingly, because I livehere and know the local wildlife bestthe new scope providedthe opportunity to write about species that do not occur in myhome state but that I have had the pleasure of meeting elsewhere.

Of the 19 species of owl in North America, 15 occur (or mayoccur) in California. Missing from my state but found in someother western states are the Northern Hawk Owl (Surnia ulula),which has been recorded as far south as Oregon; the EasternScreech-Owl (Megascops asio), an eastern species that makes it toMontana, Wyoming, and Colorado; and the largely Latin Ameri-can Whiskered Screech-Owl (M. trichopsis) and FerruginousPygmy-Owl (Glaucidium brasilianum), whose ranges includeparts of the Southwest.

Although the Snowy Owl (Bubo scandiacus) is only a visitor to some western states and does not breed south of the Artic, it iscertainly part of the Western avifauna, and a spectacular one atthat; news of a sighting of (or, much more seldom, an invasionby) this owl spreads quickly through the bird-watching commu-nity and causes pilgrimages to viewing sites. The Elf Owl (Micra-thene whitneyi) is extremely rare in California and may in fact nolonger reside here, but it is too soon to pronounce it extirpated:there are persistent rumors of sightings from the lower Colorado

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River, and the species certainly is not uncommon in parts of Ari-zona, New Mexico, and Texas.

The suggestion of the Boreal Owl (Aegolius funereus) as a Cal-ifornia species is more controversial and is based on a single ob-servers hearing its call in midwinter in our state. An inhabitant ofhigh mountains, this owl is most vocal at a time when its habitatis covered in deep snow and owl watchers are toasting their toesby the re at lower elevations. Many believe that Boreal Owls willeventually be discovered breeding in California; they are residentin central Oregon and are found as far south as northern NewMexico and occur in other western states.

Owls are memorable creatures, a happy fact for someone whowants to write a book on these wondrous birds and who is blessedwith a wide circle of friends, many of them biologists, all of thempeople who go through the land with open eyes and minds.

My most profound thanks go to my best friend and wife, Pam,my constant companion walking the elds and forests of thisworld, support system extraordinaire, sublime cook, publishedfellow scribe, editor, typist, and general factotum par excellencewho contributed immeasurably to the production of this guide.Too bad she cannot paint birds.

Near-lifelong friends have discussed owls and other raptorswith me ad innitum. My thanks to Sterling Bunnell, Steve Her-man, Ed Hobbs, Grainger Hunt, E. W. Jameson Jr., and Bob Rise-brough for exchanging ideas and observations over the years, andfor their enduring friendship. Bruce Mahall additionally has notonly spent a great many pleasant days and nights in the eld withme, at times looking for owls, but has also helped to nish many abottle of wine, often improved by the place of consumption.

I am very indebted to people who have provided me access tolive owls or frozen specimens or directed me to roadkills (of vari-able freshness). These include Nancy Anderson, Rose Britton,Seth Bunnell, Julie Burkhart, Rob and Julie Cyr, Allen Fish (whoalso helped in many other ways), Pat and Phil Gordon, SusanHeckly, Frank Marino, and Chris Peeters. Carla Cicero and JamesPatton (who was always available and willing to answer ques-tions) facilitated examining material in the University of Califor-nia at Berkeleys Museum of Vertebrate Zoology collection.

My special thanks go to Pete Bloom and Brian Woodbridge,who not only carefully read the manuscript, making numeroushelpful suggestions, but who also supplied information not yet

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S o n o r a n D e s e r t

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available in the literature. I also thank Doug Bell for his reading ofthe rst draft.

Irv Tiessen graciously provided two owl boxes for my yard (aWestern Screech-Owl promptly moved into one of them, favor-ing it over my own antiquated model) and was always happy tohelp in a variety of ways. Steve Simmons, astute observer of owls,generously allowed me the use of his slides, Barn Owl data, andnest box design.

Many other fans of owls, both amateur and professional, havegreatly contributed to this book by providing help or informationon topics too numerous to list, running the gamut from the use ofowls in Italy to the fate of a California Towhee (Pipilo crissalis) onthe high seas. They include Bud Anderson, Jack Barclay, JoelleBua, David Camilleri, Manuel Carrasco, the late HowardCogswell, Daniele Colombo, D. J. Correos, Kate Davis, PenelopeDelevor yas, Joe DiDonato, Leon Elam, Margaret Emery, SandyFerreira, Reiko Fujii, Kimball Garrett, Fred Gehlbach, GordonGould, Andrea Henke, Buzz Hull, Terry Hunt, Lloyd Ki, TimKoopmann, Hans Kruger, Lynn Kruger, Colleen Lenihan, JohnLoft, Sarah Lynch, Susan Magrino, Michelle Manhal, Je Maurer,Geo Monk, Richard Montgomery, Joe Naras, Claudio Peccati,Hans-Josef Peeters, Julian Peeters, Bob Power, Dave Quady, PatRedig, Keith Richman, Patricio Robles Gil, Ron Schlor, JohnSchmitt, Debi Shearwater, Andy Smoker, Sam Smoker, ScottStender, Chris Stermer, Diane Tiessen, George Trabert, MarilynTrabert, Rodney Tripp, Jim Turner, Brian Walton, and WendyWinstead.

Doris Kretschmer and Jenny Wapner at the University of Cal-ifornia Press championed the writing of this book, and the superbeditorial skills of Scott Norton and Kate Homan and their greatmany helpful suggestions are deeply appreciated.

Finally, I would like to thank owl researchers in general, forspending hours in the cold at times of the night when sane hu-mans are home in bed.

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Map 1 (facing page). Major geographic and vegetational features of thewestern United States.

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Boise

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P A C I F I CO C E A N

Arizona

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Siskiyou

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Shasta

Lassen

TrinityHumboldt

Tehama

GlennButte

Plumas

SierraNevada Yuba

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Sutter Placer

El Dorado

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SanJoaquin

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Nevada Yuba Sutter

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Map 2 (facing page). California counties. When counties are named inthis book, they are in California.

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INTRODUCT ION

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MANY BIRDS HAVE ADAPTATIONS so astonishing as to test our cre du -lity. The Whooping Crane (Grus americana) has a nearly ve-foot-long windpipe, partly coiled beside its breastbone, to producestentorian, distance-spanning sounds that remind us of trom-bones, and the kiwi (Apteryx), a rotund ightless bird of NewZea land, smells its quarry through the nostrils at the tip of its longbeak while truing for worms.

But owls stand out with their ingeniously modied plumage,their telescope eyes, their sound funnels, their very skulls some-times twisted asymmetrical by evolution to facilitate three-dimensional hearingall this, plus nely honed weaponry. Toobtain food in the dark presents no diculty for a deer, but whenthat food is not only highly mobile but also has an array of sharpsenses to detect a predator, the nocturnal raptors body requiressome extraordinary modications.

Owls are surely among the most readily recognized groups ofbirds in the world. Being so distinctive, it comes as no surprisethat in bird classication, owls are assigned their own order, theStrigiformes, the owl-shaped birds, separate and distinct from,for example, the Falconiformes (hawk-shaped birds).

What Is an Owl?

Linnaeus, father of animal classication, rst placed owls with thehawks, eagles, and falcons because of their hooked beaks, talon-bearing toes, and predatory lifestyle. Most ornithologists todayare in agreement that owls are actually most closely related to theCaprimulgiformes (the nightjars, nighthawks, and their allies).With these, owls have in common the often large eyes, the soft, lax plumage with intricate patterning, the rather austere colors,and anatomical and behavioral similarities (some really odd,such as grooming combs and rocking side to side when alarmed),as well as molecular (DNA) anities. The traits owls share withhawks are merely an excellent example of convergent evolution,driven here by similar food habits. But just when it seems safe todeclare owls nothing more than nightjars gone bad, additionalmolecular studies on the mitochondrial DNA of owls suggest thatthese birds in fact are related to neither caprimulgids nor hawks(Wink and Heidrich 1999).

2 I N T R O D U C T I O N

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Whereas the caprimulgiform birds are chiey insectivorous,owls would appear to have evolved in response to an incrediblyenergy-rich bonanza of food available at night: the rodents. Manymodern owls also are insect-catchers and eat other prey (a few

I N T R O D U C T I O N 3

Fig. 1. The NeotropicalNorthern Potoo (Nyctibius jamaicensis) (left) and theCommon Poorwill (repre-sented below by chicks)are members of the orderCaprimulgiformes, a groupof birds that shows manyaffinities to owls on molec-ular, anatomical, and be-havioral levels.

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even live on sh), and some y by day, but many are clearly designed to catch rats and mice in the dark. Worldwide, there are over 200 species of owls, separated into two families, the Tytonidae and the Strigidae, the latter comprising the great majority.

Ten thousand years ago, there lived in Cuba a huge kind of owlthat stood taller than three feet; it is presumed to have fed on ro-dents the size of pigs. The fossil bones of this bird indicate that itwas a kind of barn owl, a member of the family Tytonidae, whosehistory can be traced back to the Miocene, 26 million years ago,far before the appearance of hominids. Modern tytonids, sub-stantially more modest in size, are distinctly warm-temperate to tropical in distribution, suggesting that the family originatedin warmer regions. As opposed to North America, where the Barn Owl (Tyto alba) is the sole representative of the family, Australia, for example, with an overall balmier climate, is home to ve species of barn owls, including one, the Masked Owl (T.novaehollandiae), that looks like a Barn Owl on steroids andcatches rabbits with its powerful feet. It is of course still vastlysmaller than the extinct Cuban giant. The various members of thefamily are suciently similar to the Barn Owl that they are read-ily recognized as relatives, with the exception perhaps of the bayowls (for one, see the photo of the author), two tropical speciesfound in jungles and ttingly endowed with exotic-looking faces.

The various kinds of barn owls worldwide share distinctiveanatomical traits such as a heart-shaped facial disk, long legs, and,in most, a comblike middle claw (pecten) used for grooming.When molting, they replace tail feathers from the tails center out

4 I N T R O D U C T I O N

Fig. 2. The pecten (comb)on the Barn Owls middletalon is used for groomingfeathers; it is also presentin the Common Poorwill.

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toward the edges, the opposite of the tail molt of strigid owls(Gilliard 1958), which also have more circular facial disks (usu-ally resembling in outline the cut surface of a halved apple),mostly shorter legs, and no pecten. In addition, no tytonid owlhas ear tufts, a feature of many strigids. In captivity, fertile hybrideggs have been produced by members of the two families, but noyoung hatched (Flieg 1971).

Owls of the family Strigidae are not only represented by vastlymore species but occur in a far greater range of sizes and appear-ance. From the pygmy-owl (Glaucidium), scarcely larger than asparrow, to the massive eagle-owl (Bubo), these birds occupyevery major terrestrial habitat on Earth and are found on everycon tinent except Antarctica. Secretive as they are, it comes as nosurprise that new species are still being discovered, and DNA andvocalization studies may reveal that a known kind of owl actuallyhides a second species within its ranks, virtually identical in ap-pearance.

Owls in California and the West

All the owls native to North America north of Mexico can befound in the West, and California alone is home to more than adozen dierent kinds, placing it at or near the top in species abun-dance when compared to other U.S. states, although a few typesare very rare here.

No California county is without two or three species, andmost have substantially more; some owls are in fact common andlive comfortably in the presence of humans. In the oak-laurel and oakgray pine woodlands of the Coast Ranges and placeswhere these habitats have been integrated into suburban devel-opments, as many as six species can be heard calling and singingon a night in late fall, winter, or early spring: the Great Horned(Bubo virginianus), Long-eared (Asio otus), Western Screech-(Megascops kennicottii), Barn, Northern Pygmy- (Glaucidiumgnoma), and Northern Saw-whet (Aegolius acadicus) owls all mayannounce themselves during a walk along an otherwise silentroad after nightfall.

Such a stroll can develop into an exciting outing. The aspiringowl watcher soon discovers that owls produce a bewildering array

I N T R O D U C T I O N 5

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Fig. 3. Female Burrowing Owl and some of her prefledged young, onelying down to rest, another turning its head sideways, behavior the func-tion of which is not clear.

Fig. 4. Tule Lake and the Klamath Basin in northern California are famousfor their wintering concentrations of waterfowl, Bald Eagles (Haliaeetusleucocephalus), and other raptors. It is an excellent place to see Short-eared Owls (Asio flammeus) as well as some other owl species.

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of vocalizations, including some that seem to have sprung fromthe imaginations of the brothers Grimm, turning the dark woodinto an abode of trolls and gremlins. Even an experienced owlercan be unnerved temporarily by what sounds to be the scream ofa murder victim in extremis. And there are other nocturnal surprises: the sharp-antlered Black-tailed Deer buck (Odocoileushemionus), confused by your ashlights beam, approachingwithin touching distance; the Bobcat (Felis rufus) that slips intothe roadside bushes with a re-eyed backward glance; the Com-mon Poorwill (Phalaenoptilus nuttallii) whirling up on mothwings from the road; and of course, always, the rustling in thebrush that is entirely too loud to be made by just a rabbit.

Conversely, for the more leisure-oriented owl watcher, there isthe unalloyed pleasure of sitting in the comfort of your car on abright morning in late spring and watching the endlessly amus-ing carryings on of a family of Burrowing Owls (Athene cunicu-laria) at the mouth of their burrow; and coming across a roostingowl during a brilliant summers day walk in the park is always a happy event. With experience, you can nd your favorite birdsin just about any habitat, from the Anza-Borrego Desert to theoak woodlands of Pinnacles National Monument and the conif-erous fog-shrouded gloom of the northwest coast, and your en-counters need not involve strenuous exercise or after-dinner forays, though these tend to be the most fruitful.

I N T R O D U C T I O N 7

Fig. 5. The toweringredwoods of Califor-nias north coast arefamously home toNorthern SpottedOwls (Strix occiden-talis caurina) andalso to several otherspecies.

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Most owls are closely associated with trees of some sort, andtheir bodies reect this. And while, like hawks, they are birds ofprey, they show much less diversity in hunting methods and inbody and wing shapes than do the diurnal raptors. Because theforaging habitats and foraging styles are so similar in most owls,they are remarkably alike in build, though some have longerwings than others or longer legs. Notwithstanding the dierencesin markings between the various western species, they all sharemuch the same similarly distributed colors, and only three defythis convention (the Barn Owl, the Great Gray Owl [Strix nebu-losa], and Snowy Owl [Bubo scandiacus]); one, the NorthernHawk Owl (Surnia ulula), abandons the traditional shape andlooks more like a hawk.

8 I N T R O D U C T I O N

Fig. 6. This modest strip of oak riparian woodland along an ephemeralstream amidst grassland in central California measures less than 1 km(less than .5 mi) in length. In August 2005, it held eight Barn Owls, onepair of Great Horned Owls, and at least one pair of Western Screech-Owls. Circled UFO is a flying Barn Owl.

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