Natural History of Birds:
notes on a 2007 UCSC summer-school intensive
taught by Prof. W. Breck Taylor
1. Wings; flight; field observations in redwood glades
- Natural History: the study of nature by direct observation.
- A naturalist needs no special equipment or training:
(1) observe actively;
(2) ask questions;
(3) offer explanations.
- Bird evolution and adaptation is predicated on the need to fly.
- light weight; light boned. Heaviest bird is a swan (~ 35 pounds).
- compact body in most birds because all muscles involved in flight are in the
- lay hard-shell eggs so that they do not have to carry the weight and do not have to lactate.
- typically (because bones are so light) a bird's feathers weigh more than its bones.
- contour the bird aerodynamically.
- are (like hair) not alive and so they don't need constant maintenance (like the brain or heart).
- velcro-like structure rezips if damaged.
- provide flight.
- each is a tiny air foil.
- Primary feathers on the hand bones provide thrust for propulsion.
- Secondary feathers on the rigid arm bones provide lift to overcome gravity.
- Wing has a thick smooth front end an a slight camber (curve) to create the
Bernoulli effect (air passing above the wing has to go further around the wing than
air passing below the wing) leading to lift.
- Types of flight:
- Soaring (at stable height above ground) on thermals or on slope or air
rising at cliff face or forest edge.
- Gliding in a steady decline. Migration is often done by a repeated sequence
of ascending a thermal then gliding, which takes minimal effort, just a change of
the angle of attack.
- Flapping flight, which requires 10-to-100-times the energy of non-flapping flight.
- 30-40 mph sparrows
- 40-60 mph ducks
- 100-260 mph has been estimated for peregrine falcons in a stoop (power dive).
- Over 200 mph recorded for an Asian swift in level flight.
- Wing types:
- Elliptical: short, wide. Small land birds.
Controlled flight in small areas and forests
at medium speed.
Larger surface area so increase in lift, drag, and cost to flap.
Better for soaring and control at slow speeds: condor, pelican.
- High-speed: short and narrow. Lowest surface area so cheapest
to flap; least drag.
Preferable for diving sea birds.
- High-aspect-ratio: long and narrowed.
Lots of lift in long secondary feathers.
Good at relatively high speeds.
Disaster on landing because of the high turbulence and back-suck on slowing down
(compare with pull-back on stopping a power boat).
- Joseph Grinell's method of taking field notes:
detailed, specific, precise.
2. Avian origins and systematics
- Reviewed birds observed by two groups of students in the last hour of previous class;
one group was in redwoods and glades and quarry;
the other group in redwoods and at a pond:
- 8 reported by one group and 5 by the other; all but two are perching birds
- Only two species were seen by both groups.
- We can use common name for a bird (as opposed to a mammal or a plant) because bird names are
Annual committee makes changes as needed:
Dark-eyed Junco was previously Oregon Junco.
- Standardized "alpha code" of 4 letters:
- Default is first two letters of the 2-part common name. WIWA for Wilson's Warbler.
- Hyphenated name: use first letter of each part. WTSW for White-Throated Swift.
- Single name: first 4 letters. MALL for Mallard.
- Evolutionary history determined by:
- Direct observation.
- Biochemical and genetic traits.
- Birds share traits most extensively with reptiles.
More closely related to reptiles than amphibians (which are more like fish) are related to reptiles.
- Both have scales.
- Both have a shelled, amniotic egg.
- Skeletal similarities include cranial kinesis (both upper and lower jaws move).
- LAB to look at:
3. Field trip to Davenport cliffs (seabirds) and Rancho del Oso (chaparral and forest birds)
- Davenport cliffs (seabirds).
Sunny and calm July morning, 0830-0930: An hour on the cliffs with binoculars and spotting scopes.
Birds seen [in square brackets if identified by others but not seen by me]:
- [BRBL: Brewer's Blackbird. On beach. Aggressive. Black with cream-colored eye (male).]
- BRCO: Brandt's Cormorants. Perched on pylons of abandoned Davenport wharf.
Nesting. Mostly the turquoise throat patch was very small, as this is late in their breeding season.
Chicks spotted beneath the nesters.
Some of the males returned with a little more seaweed for nests.
One returned with fish.
- BRPE: Brown Pelican.
A few with white heads.
A few brown all over (juveniles).
- CAGU: California Gull. Yellow legs. Red and black spots on bill.
- CATE: Caspian Tern. White and pointed-wing. Flying fast, parallel to shore and a hundred yards out to sea.
- PIGU: Pigeon Guillimot. Black with paddling red feet.
Relatively heavy bird (like most divers); flies close to water for edge-effect lift.
- WEGU: Western Gull. Pink legs. Red spot on bill. Large bill (compare CAGU).
Also: heard Red-winged Blackbird;
glimpsed small birds chasing off a raven (or crow) from the cypress trees we were shaded by.
- Rancho del Oso (chaparral and forest).
Sunny and windy July morning, 1015-1200: A leisurely amble with binoculars
for about a mile inland,
through very varied habitat from a marsh lake, through chaparral, into mixed conifer-deciduous forest bordering on riparian.
Birds seen [in square brackets if identified by others but not seen by me]:
- ACWO: Acorn Woodpecker.
- ANHU: Anna's Hummingbird. Green. No flashy flying or throat colors so probably female.
- ALHU: Allen's Hummingbird. Light brown. No flashy flying or throat colors so probably female.
- [CAQU: California Quail.]
- CBCH: Chestnut-Backed Chickadee. Black cap, white cheeks, chestnut back.
- CORA: Common Raven. Diamond-shaped ('wedge-shaped') tail (versus fan-shaped tail of the crow).
- Duck (mallard?) flew by fast and low at the marsh.
- PUFI: Purple Finch.
- RTHA: Red-Tailed Hawk.
- SCJA: Scrub Jay.
- STJA: Steller's Jay.
- Swallow. White undersides. Compact wings. Quick and agile.
- TUVU: Turkey Vulture.
- [BTPI: Band-Tailed Pigeon. Banded tail.]
- Birds have very high food requirement due to:
- High Basal Metabolic Rate (BMR).
- 40-42°C body temperature; higher than mammals.
- Small and readily lose heat due to high surface-to-volume ratio.
- Very active lifestyle:
- Cost of flight raises the metabolic rate (MR) to 5-to-25 time BMR.
- Food consumed per gram of a bird increases as total mass decreases:
||Amount of food consumed
||Weight of food eaten daily as percent of body weight
||Approximate body weight
[Reed Hainsworth and Larry Wolf (at http://www.hummingbirds.net/hainsworth.html,
retrieved 7 July 2007) report data for hummingbirds:
"Hummingbirds must eat more than their weight in food each day".]
(at http://www.learner.org/jnorth/search/HummerNotes3.html, retrieved 7 July 2007) report data for
"Hummingbirds burn food so fast they often eat 1.5 to 3 times their body weight in food per day".
- Small birds can store no or little fat (in normal circumstances) because it is too heavy.
- While a male emperor penguin survives 90-120 days without food, on average:
- A chickadee needs to eat a seed every 30 seconds.
- A wren needs to eat a seed every 10-15 seconds.
- Finding food requires steps to:
Foraging is costly:
- Make the energetic choice most cost-beneficial (i.e. appropriate) to the moment.
- The most you forage, the more the risk of predation.
Foraging techniques include:
- Aerial insect capture by open-mouth sweeping.
e.g. swifts, many swallows.
Tool: huge mouth and small beak.
- Aerial insect capture by hawking, i.e., perching then flying out to a specific insect:
e.g. flycatchers, kingbirds, sometimes waxwings.
Returns to same perch to each prey.
- Insect gleaning,
taking insects, spiders, slugs, etc. from vegetation.
Perch gleaning without leaving perch.
Sally gleaning by sitting, watching vegetation nearby, and flying out to pluck prey.
Hoover gleaning of hovering to remove food from vegetation surfaces.
- Probing: plunge beak into mud, tree bark, etc. for prey.
- Pounding: hammer on tree trunks and limbs to disturb insects enough that they
come to the surface.
- Chiseling: create hole through which the bird can insert its tongue.
e.g. Pileated Woodpecker, sapsuckers, oystercatchers.
- Raptorial predation by pouncing: pounce on a target from midair and pin it against the ground.
e.g. many hawks, Great Horned Owl and other owls.
- Raptorial predation by stooping: drop through the air extremely quickly to snatch a bird
or insect in midair.
e.g. many falcons such as Peregrine Falcon.
- Surface dive: From a swimming position, go below the water.
e.g. diving ducks, grebes, cormorants, loons, Hooded Merganser.
- Plunge dive: From air, go below the water.
e.g. osprey, catching prey with talons.
e.g. Brown Pelicans, auks, gannets, and kingfishers, catching prey with long pointed beak.
- Stalking and stabbing: stand still or walk slowly until the prey appears and they grab it.
e.g. herons, egrets, storks in water.
e.g. plovers, thrushes, and larks on the land.
- Sifting with a specialized bill.
e.g. Roseate Spoonbill.
- Pecking and biting of seeds or vegetation.
- Nectar feeding.
- Water surface feeding. Also called dabbling:
moving beaks rapidly on the surface to pick up food.
e.g. Northern Shovelers; phalaropes (with the addition of spinning to create a
vortex that brings food to the surface).
- Searching leaf little. May include leaf tossing.
e.g. Eastern Towhees and Fox and White-crowned Sparrows kick with both feet;
grouse and turkeys scratch with one foot at once;
thrashers 'thrash' with their beaks.
- Find or detect, particularly by sight, hearing, and smell.
- Capture or gather. Bill design affects how you do so.
- Process or handle. Most eat the prey whole.
Food passes down the esophagus to the crop (begins digestion in this storage chamber).
Then to preventriculous for chemical digestion;
an eater of mice can dissolve a mouse in an hour;
a vulture can dissolve bones in an hour.
Then to the gizzard for physical digestion of anything remaining such as seeds.
- LAB to look at the bodies of:
- Perching birds: Seed eaters; fruit eaters; insectivores.
- Non-perching birds: hawk, eagle, vulture, owl, ...
5. Field trip to Elkhorn Slough by
waders and water birds
Species List in taxonomic order:
6. Seabird and shorebird ecology
- An "aquatic bird" makes its living in the water, a source of food, drink, and habitat.
- A "marine bird" makes its living in salt water, for food, drink, and habitat.
- Approximately 350 species of all 9700 species; i.e. about 3.5%.
marine mammals are 3.5% of all mammals.]
Why so few?
- The ocean is a uniform habitat that lacks the many niches of land.
- The older evolution of seabirds than perching birds indicates the
difficulty of transitioning from life on land to life at sea.
- But abundance of sea birds and land birds is about the same.
- Physical challenges of the sea environment compared with life on land:
Water steals heat 50-100 times faster than air at same temperature.
Birds have trouble especially because:
(a) Small and thus have a high surface-to-volume ration.
(b) Can't or don't store fat (except for migration).
(c) >40-42°C body temperature (higher than mammals).
Preen gland (uropygial) has waterproof substance the bird works into
contour feathers, trapping a layer of air against the skin. Oil-spill deaths
result from birds being unable to put air under feathers.
Limitations for divers of this air:
- Air causes buoyancy, competing with their intent to dive.
- The deeper they go, the more the air is compressed so the more danger of their getting cold.
- Saltier. Ocean is 3.5% (35o/oo), while bird (like humans) have
saltiness of 1.8% (18o/oo).
The body will lose water to try to dilute the sea.
Marine birds get water from their prey; salt is on the surface of the fish, though not 'a lot'.
Plankton-eating (planktivorous) birds have specialized salt-filtering organs
below the eyes above the beak.
- Denser (water is 700 times as dense as air). Limitation for divers is buoyancy.
- Lacks oxygen below the surface.
- Dark below the surface: no light except in the top 100 feet (California coast) to 100 meters (tropics).
- Feeding categories:
- Feed above the water in the air on a marine-based prey.
Wait for prey such as small
dolphins to jump;
jaeger and frigate bird ("the best flying bird in the world")
steal other birds' prey or force regurgitation.
- Feed on the surface (top 1 meter). e.g. gull.
- Plunge diving, using gravity. e.g., tern, pelican.
- True diving: sit on surface then dive and lunge looking for prey.
e.g. guillemot, cormorant, penguin.
- Diving birds that propel under water by kicking with feet stick their wings behind them.
Feet are off the back end.
e.g. loon, grebe, cormorant.
Hard to walk on land.
Sometimes scuttle on bellies.
- Diving birds that propel by flapping wings.
Costly so want wings with minimal surface area: short, narrow, stubby.
May sacrifice flight ability.
- Wing shape:
- Aerial seabirds: largish light-weight wings. Therefore low wing loading.
- Diving seabirds: heavy body to overcome buoyancy;
Therefore high wing loading with little lift.
Flight attempts may look like whirring.
- Levels of marineness:
- 3° = The least marine. Does not swim. Feeds along shorelines primarily
by wading primarily.
- 2° = Swims. Feeds in marine waters part of the year or part of their lives.
A marine bird.
- 1° = Swims. Feeds in marine habitats all year and nowhere else.
A marine bird.
- Best reference:
Seabirds : a natural history
by Tony [A.J.] Gaston.
7. Migration and molt
Costs (in addition to staying alive):
- Reproduction to replace yourself: adds 50% to the average daily cost.
The most costly so timed when there is the most to eat
(in the spring in the North Hemisphere),
with sunshine increasing and increases in plant and insect production.
- Molt to replace your feathers: adds 25% to the average daily cost.
Can be 50%.
Typically once per year.
Takes a few weeks to a few months.
Some birds molt through-out the year; eagles take over 2 years and molt symmetrically,
the gap moving up or down the wings
in hawks, songbirds, seabirds.
Some (like duck or others with small wing on a heavy bird)
make an elliptical molt:
drop all flight feathers at once;
eclipse plumage is drab and dark.
Birds like ducks cannot fly if lose 2-3 feathers,
so they hide out till the feathers grown back.
Some birds molt more than once in a year (into and out of breeding plumage).
Rarely females molt in/out breeding plumage; e.g. female phalarope with reverse dimorphism.
Some birds molt for camouflage, temperature change, etc.
Generally believed to be controlled by length of sunlight.
- Migration: adds 25% to the average daily cost.
- Migration is the seasonal round trip movement by all or part of a population
to or from a breeding area.
Tied to seasonal peaks in resources.
- Not all movement is migration. 25% of California birds are not migratory.
(a) Red-shouldered hawk disperses from the breeding ground but this is not migration.
(b) Cormorants on the Monterey Bay have a daily or home range that lets them circle
- Some go little distance. California quail walks and not far from its
birthplace. California towhee is usually found within a mile of
where it is born.
- Some go immense distances.
The Arctic Tern flies pole-to-pole.
- "Complete migration" if all of the population migrates.
- "Partial migration" if some (typically the younger
or older birds don't go).
- If conditions unpredictable year-to-year, genetic success
is maximized if some migrate and some stay home.
More on migration:
- Latitude Migration: North-South.
- Elevation Migration: into the mountains in summer; to the coast and/or lowlands in winter.
- Fast Migration: if no way to feed along the way.
Build weight up to double with layer of fat.
e.g. Arctic sandpiper nests in the arctic, winters in south hemisphere,
flies 50 m.p.h., 24 hours per day, 7 days/week.
- Protracted Migration: stop along the way (most common form).
Land birds fly in the calm air at night, sleep and rest and hide in the day.
Hawks fly by day with thermals.
- Leapfrog Migration: e.g. white-crowned sparrow.
One group is sedentary (not migrating).
A group immediately north (e.g. Puget Sound group of white-crowned sparrow)
migrates immediately south of the sedentary group.
A group immediately north of the 2nd group (e.g. Alaskan gambels)
migrates immediately south of both groups.
- Why migrate?
- Take advantage of seasonal reduction of resources.
- Avoid seasonally stressful weather and environmental conditions
(winter chill, heat, drought).
- Reduce impact of year-round feeding in the place where you live.
- Vary diet; supplement with what you don't get if you stay home.
- Why not migrate?
- Energetically costly.
e.g. Warbler from Central America to California burns fat equivalent to the gas that a car would
burn for a trip of 72,000 miles.
- Risky: Your territory might not be available on your return.
- Risky: 50% of the migrating birds die (particularly the young birds).
- Migration: how?
- Orientation: figure out in general the current location.
- Navigation: locate a particular location.
Mechanism may include:
- Celestial cues: sun, stars.
- Chemo-receptors to get back to location where born.
- Innate sense; preprogrammed algorithm gets you to the general target location and you figure it out
when you get there.
- Polarization detection of occluded sunlight.
- Pressure. Storm systems in spring and fall.
- UV sensors.
Note that migrating birds can become completely disoriented in fog and have to make emergency landfall.
8. Field trip to Big Sur Ornithological Laboratory (bird banding laboratory)
and Andrew Molera State Park (riparian birds)
Species List in taxonomic order:
9. Communication and nesting
- Sounds. Only birds, humans, and
dolphins have developed complex communication sounds.
Vocal bird sounds are
Non-vocals sounds included percussive tapping with beak, feet scuffling, wings.
No physical difference in how songs and calls are made. Main comparisons:
|Complex: lots of notes and melodies
|Mainly males sing.
||Both genders call.
|During breeding season.
||For many purposes.
|Learned by mimicry of parents or
(to avoid inbreeding) neighbors.
Calls can be social among groups or individual expression:
- Attract prey by mimicking it.
- Begging: e.g. chicks.
- Contact: keeps a feeding flock together during feeding (e.g. chickadee) or
a traveling flock together during migration.
- Defend feeding territory (as opposed to breeding territory, which is
defended by song).
- Distress: "get out of here, it's not safe", such as starling.
- Information that food is here: e.g. gulls as first finders;
(a) They will benefit from reciprocity of finding;
(b) A larger group may be more successful at foraging,
both by finding more thoroughly and by preventing prey from escaping.
- Mimic predator.
- Rally: "come and help", such as a crow or raven threatened by a hawk
and calling for a mob.
- Threats (such as gull's "go away" call).
Creation of bird sound:
- Sirynx: two paired passages containing
vocal chords at bottom end of trachea.
Can make more than one sound at once.
- Birds use about 100% of air to produce sound.
Humans use only 5%.
- Some birds have no nerve attachments to sirynx and can only grunt.
- Loud trumpet or bugle sound of the sandhill cranes; chamber like a horn.
a traveling flock together during migration.
- Vary amplitude (loudness, intensity).
Choose which pitches to make louder or softer.
Effect of noise in the environment: you may have to sing louder as humans create more noise.
Dippers (live by waterfalls and cataracts): very high-pitched song to cut through the stream's roar.
- Vary frequency (pitch). Lower has a longer wavelength and travels longer distances.
e.g. hawk or owl.
Some even communicate with infrasound: cassowary and others.
Higher pitch is less modified by wind and temperature change.
Alarm call: whistle on single frequency without harmonics.
Multiple frequencies at once: screeches, trills, complex songs.
- Vary syntax (melody).
How many notes do you use and how do you arrange them?
||5-15 notes per bird
|Thrasher (may have the most)
||~ 1000 songs.
|Reed warbler (European)
||Even more than the thrasher.
Songs are important: songbirds make decisions almost entirely based on songs,
which are believed to:
- Maintain the species barrier: song as breeding barrier.
- Synchronize breeding of males and females.
- Establish territory for males and attracts a mate.
Sing on the edge of the territory, showing its size.
- Through variety of song, suggest experience and health.
- Express desire and availability: unmated mocking birds sing all the time.
Song sparrows sing 9 hours/day when seeking a mate, about 20,000 times per day!
And forage-feed 9 hours/day.
Singing takes a lot of energy.
So cut back on singing when find a mate.
- The cost of song diversity is the sacrifice of recognizing one's neighbor.
- Best mimics are parrots.
Communication and cognition tested through cognitive tests for recognizing symbols,
making connections, showing elasticity in thinking:
- Parrots have outperformed
dolphins and seals in making leaps of understanding.
- Baby bird arrives with a template.
- 20-80 days critical learning stage where you
have to hear your father or a neighboring male.
- Male song crystallizes at about 10 months.
What does a male's song tell a female:
- I'm here.
- I'm male.
- I'm a spotted towhee (or whatever).
- I'm available.
- I'm in breeding condition.
- I'm fit and healthy (how well I sing).
- I have a territory.
- It is big.
- It is good.
- It is safe from predators: I am out here singing.
- I sing a lot: I am a good provider and don't have to be always foraging.
- I'm experienced.
- I'm local so I know the place well.
10. Mating systems and social behavior
Interesting, well-studied, relatively easy to study (compared with flight, say) because localized.
- Natural selection: differential reproductive success among animals in nature.
Individual birds select the "best" mate with the "best" traits.
- Sexual selection: Traits that make you better at reproduction and have
no other value. Juveniles do not show these traits to keep them out of the gene pool till mature.
Bigger birds tend to be more similar and have fewer and weaker such traits,
as do shore and sea birds.
Classical view of the pair bond is a function of dimorphy.
Most birds have differences in breeding plumage, sometimes size, etc.
But 90% of all birds are monogamous, 98% of sea birds.
For mammals in the wild, the female expends orders of magnitude more effort
than the male.
Male and female birds in the wild expend similar efforts, including brooding the eggs and feeding the chicks.
- Biparental care: When both parents are required for the chick to survive,
"obligate" monogamy, e.g. when:
- Harsh environmental conditions
(cold, heat, wind, etc) require one parent to stay with the chick while the other
parent forages for provisions.
- Predation is high.
- Prey is low, so the forager must go long distances from the nest to feed.
Exceptions include frigate birds and ducks.
- "Facultative" monogamy: One parent could raise the chicks without help,
but two parents result in more offspring.
- Extra-pair copulation (EPC) occurs, however, if there is opportunity.
Female ducks prevent this by flying to a secluded site, the male following them,
not participating in child care, but also lacking opportunity for EPC.
- In some species (e.g. Red-winged Blackbird),
the female chooses monogamy when food is plentiful even at outlying sites,
but polygeny when food is scarce and to guarantee the survival of
her offspring she requires the most successful territory, already held
by a male and another female.
- A lekking ground is cleared ground, an open plain,
whose only use is for male display.
e.g. the grouse.
A female chooses a displaying male, they fly away to copulate,
then the female nests and carries out all the work,
while the male returns to the lekking ground in hopes of another partner.
- Solitary leks are made by bower birds.
- Solitary leks are made by some jungle birds that clear a tunnel in the jungle,
removing twigs from the ground, and flies (about 10 meters).
Usually no song but wing clicking.
- "Polyandry": e.g. Phallaropes where the females are big and bold,
lay eggs, then leave the male to stay and raise the chicks.
Hummingbirds mate and move on.
- Cooperative nesting systems:
- Single nest with one egg from each female; one male takes care of those.
- Chicks stay around and help with next year's brood, e.g. scrub jays in Florida.
- Relatives and descendants of parents stay in a community;
only the parents breed; when that generation dies, the young females leave as a group,
while the males remain waiting for new females.
e.g. Acorn Woodpeckers with granaries in North California.
"Almost no divorce among successful pairs."
11. Bird conservation, part One
Student presentations on:
- Burrowing Owl: range and number reduction. Need 10-or-so hectares (25 acres) of appropriately undisturbed habitat.
- Bird-friendly coffee certified by Smithsonian Migratory Bird Center; rustic (natural) shade and planted shade need to
provide a minimum of 40% canopy; minimum of 10 tree species.
Currently 33 certified consortiums include about 2000 growers.
- Northern Spotted Owl: an indicator species;
needs 3,000 acres per Spotted Owl, with habitat including unthinned (and prey rich) under-story; prefers old-growth.
- Clapper Rail: population collapse and partial recovery.
- Effects of increased ambient noise on bird song: reduction of pairing success by 25%
at loud sites than quiet sites; increase of loudness of birdsong at loud sites.
- Peregrine Falcon: A successful conservation story; numbers fell by 90%
to a few hundred in the 1970s because of DDT-weakened egg shells in predator birds.
- Impacts of long-line fishing on albatrosses and gill-net fishing on Common Murre.
12. Bird conservation, part Two
Student presentations on:
- Plastic Pollution of the Ocean, particularly its effects on the Albatross.
- Wind turbines and avian death.
- Bird mortality in the domestic realm: window collisions and cats:
See also Ariadne's web for
information on cats killing over a quarter billion birds in USA per year,
including data that
"the average urban cat in Wichita kills 4.2 birds per year."
- 1-10 birds killed by each building per year, including by window collisions in residential areas.
- This totals 98-980 M birds per year.
- 90 M cats in USA living with owners; 35% exclusively indoors.
- 60-100 M feral cats in USA.
- Effects of DDT on Bald Eagles and other birds.
- Recovery projects of Snowy Plovers and Great Lakes Piping Plovers.
- Condor recovery program.
- Discovery of the Marbled Murrelets and their subsequent reduction.
- The Iwa [thief] or Great Frigate Bird.
by Don Stap.
- The Birds of California
by Arnold Small.
- Handbook of Bird Biology
edited by S. Podulka et al.
- National Geographic Field Guide to Birds of North America, 5th edition
edited by Jon L. Dunn and Jonathan Alderfer.
- Seabirds: A Natural History
by A.J. Gaston.
- The Sibley Field Guide to Birds of Western North America
by David Allen Sibley.
- The Sibley Guide to Birds
by David Allen Sibley.
- Sibley's Birding Basics
written and illustrated by
David Allen Sibley.
The Ecology Footprint quiz