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

  1. Natural History: the study of nature by direct observation.
  2. A naturalist needs no special equipment or training: (1) observe actively; (2) ask questions; (3) offer explanations.
  3. Bird evolution and adaptation is predicated on the need to fly.
  4. Morphologically:
    1. light weight; light boned. Heaviest bird is a swan (~ 35 pounds).
    2. compact body in most birds because all muscles involved in flight are in the central cavity.
    3. lay hard-shell eggs so that they do not have to carry the weight and do not have to lactate.
    4. feathers:
      • 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.
  5. Flight:
    1. Primary feathers on the hand bones provide thrust for propulsion.
    2. Secondary feathers on the rigid arm bones provide lift to overcome gravity.
    3. 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.
    4. Types of flight:
      1. Soaring (at stable height above ground) on thermals or on slope or air rising at cliff face or forest edge.
      2. 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.
      3. Flapping flight, which requires 10-to-100-times the energy of non-flapping flight.
    5. Speed:
      1. 30-40 mph sparrows
      2. 40-60 mph ducks
      3. 100-260 mph has been estimated for peregrine falcons in a stoop (power dive).
      4. Over 200 mph recorded for an Asian swift in level flight.
    6. Wing types:
      1. Elliptical: short, wide. Small land birds. Controlled flight in small areas and forests at medium speed.
      2. Slotted. Larger surface area so increase in lift, drag, and cost to flap. Better for soaring and control at slow speeds: condor, pelican.
      3. High-speed: short and narrow. Lowest surface area so cheapest to flap; least drag. Preferable for diving sea birds.
      4. 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).
  6. Joseph Grinell's method of taking field notes: detailed, specific, precise.

2. Avian origins and systematics

  1. 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:
    1. 8 reported by one group and 5 by the other; all but two are perching birds
    2. Only two species were seen by both groups.
  2. We can use common name for a bird (as opposed to a mammal or a plant) because bird names are unique worldwide. Annual committee makes changes as needed: Dark-eyed Junco was previously Oregon Junco.
  3. Standardized "alpha code" of 4 letters:
    1. Default is first two letters of the 2-part common name. WIWA for Wilson's Warbler.
    2. Hyphenated name: use first letter of each part. WTSW for White-Throated Swift.
    3. Single name: first 4 letters. MALL for Mallard.
  4. Evolutionary history determined by:
    1. Direct observation.
    2. Biochemical and genetic traits.
  5. Birds share traits most extensively with reptiles. More closely related to reptiles than amphibians (which are more like fish) are related to reptiles.
    1. Both have scales.
    2. Both have a shelled, amniotic egg.
    3. Skeletal similarities include cranial kinesis (both upper and lower jaws move).
  6. LAB to look at:
    1. Wings.
    2. Feathers.
    3. Skeletons.

3. Field trip to Davenport cliffs (seabirds) and Rancho del Oso (chaparral and forest birds)

  1. 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]:
    1. [BRBL: Brewer's Blackbird. On beach. Aggressive. Black with cream-colored eye (male).]
    2. 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.
    3. BRPE: Brown Pelican. A few with white heads. A few brown all over (juveniles).
    4. CAGU: California Gull. Yellow legs. Red and black spots on bill.
    5. CATE: Caspian Tern. White and pointed-wing. Flying fast, parallel to shore and a hundred yards out to sea.
    6. PIGU: Pigeon Guillimot. Black with paddling red feet. Relatively heavy bird (like most divers); flies close to water for edge-effect lift.
    7. 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.

  2. 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]:
    1. ACWO: Acorn Woodpecker.
    2. ANHU: Anna's Hummingbird. Green. No flashy flying or throat colors so probably female.
    3. ALHU: Allen's Hummingbird. Light brown. No flashy flying or throat colors so probably female.
    4. [CAQU: California Quail.]
    5. CBCH: Chestnut-Backed Chickadee. Black cap, white cheeks, chestnut back.
    6. CORA: Common Raven. Diamond-shaped ('wedge-shaped') tail (versus fan-shaped tail of the crow).
    7. Duck (mallard?) flew by fast and low at the marsh.
    8. Junco.
    9. PUFI: Purple Finch.
    10. RTHA: Red-Tailed Hawk.
    11. SCJA: Scrub Jay.
    12. STJA: Steller's Jay.
    13. Swallow. White undersides. Compact wings. Quick and agile.
    14. TUVU: Turkey Vulture.
    15. [BTPI: Band-Tailed Pigeon. Banded tail.]

4. Feeding

  1. Birds have very high food requirement due to:
    1. 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.
    2. Very active lifestyle:
      • Cost of flight raises the metabolic rate (MR) to 5-to-25 time BMR.

  2. 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
    Chickadee 3.5 gm 35% 10 gm
    Jay 10 gm 10% 100 gm
    Raven 40 gm 4% 100 gm

    [Reed Hainsworth and Larry Wolf (at, retrieved 7 July 2007) report data for hummingbirds: "Hummingbirds must eat more than their weight in food each day".]

    [Journey North (at, retrieved 7 July 2007) report data for hummingbirds: "Hummingbirds burn food so fast they often eat 1.5 to 3 times their body weight in food per day".

  3. Small birds can store no or little fat (in normal circumstances) because it is too heavy.

  4. While a male emperor penguin survives 90-120 days without food, on average:
    1. A chickadee needs to eat a seed every 30 seconds.
    2. A wren needs to eat a seed every 10-15 seconds.

  5. Finding food requires steps to:
    1. Search. 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. e.g. hummingbirds.
      • 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.
    2. Find or detect, particularly by sight, hearing, and smell.
    3. Capture or gather. Bill design affects how you do so.
    4. 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.
    5. Digest.

  6. LAB to look at the bodies of:
    1. Perching birds: Seed eaters; fruit eaters; insectivores.
    2. Non-perching birds: hawk, eagle, vulture, owl, ...

5. Field trip to Elkhorn Slough by kayak: waders and water birds

Species List in taxonomic order:

Clark's Grebe				
Brown Pelican			
Double-crested Cormorant
Pelagic Cormorant				
Great Egret				
Snowy Egret				
Turkey Vulture			
Red-tailed Hawk			
Northern Harrier				
White-tailed Kite				
Black-bellied Plover				
Greater Yellowlegs				
Long-billed Curlew				
Marbled Godwit				
Western Sandpiper				
Dowitcher sp.				
Western Gull		
Ring-billed Gull				
Caspian Tern			
Elegant Tern				
Forster's Tern				
Barn Swallow		
American Crow				

6. Seabird and shorebird ecology

  1. An "aquatic bird" makes its living in the water, a source of food, drink, and habitat.

  2. A "marine bird" makes its living in salt water, for food, drink, and habitat.
    1. Approximately 350 species of all 9700 species; i.e. about 3.5%. [Similarly 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.
    2. But abundance of sea birds and land birds is about the same.

  3. Physical challenges of the sea environment compared with life on land:
    1. Colder. 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.
    2. 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.
    3. Denser (water is 700 times as dense as air). Limitation for divers is buoyancy.
    4. Lacks oxygen below the surface.
    5. Dark below the surface: no light except in the top 100 feet (California coast) to 100 meters (tropics).

  4. Feeding categories:
    1. 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.
    2. Feed on the surface (top 1 meter). e.g. gull.
    3. Plunge diving, using gravity. e.g., tern, pelican.
    4. True diving: sit on surface then dive and lunge looking for prey. e.g. guillemot, cormorant, penguin.

  5. Streamlining:
    1. 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.
    2. Diving birds that propel by flapping wings. Costly so want wings with minimal surface area: short, narrow, stubby. May sacrifice flight ability.

  6. Wing shape:
    1. Aerial seabirds: largish light-weight wings. Therefore low wing loading.
    2. Diving seabirds: heavy body to overcome buoyancy; tiny wings. Therefore high wing loading with little lift. Flight attempts may look like whirring.

  7. Levels of marineness:
    1. 3° = The least marine. Does not swim. Feeds along shorelines primarily by wading primarily.
    2. 2° = Swims. Feeds in marine waters part of the year or part of their lives. A marine bird.
    3. 1° = Swims. Feeds in marine habitats all year and nowhere else. A marine bird.

  8. Best reference: Seabirds : a natural history by Tony [A.J.] Gaston.

7. Migration and molt

Costs (in addition to staying alive):

  1. 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. Obligatory.

  2. 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. Obligatory.

    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.

  3. Migration: adds 25% to the average daily cost. Optional.
    1. 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.
    2. 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 the Bay.
    3. 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.
    4. Some go immense distances. The Arctic Tern flies pole-to-pole.
    5. "Complete migration" if all of the population migrates.
    6. "Partial migration" if some (typically the younger or older birds don't go).
    7. If conditions unpredictable year-to-year, genetic success is maximized if some migrate and some stay home.

More on migration:

  1. Latitude Migration: North-South.

  2. Elevation Migration: into the mountains in summer; to the coast and/or lowlands in winter.

  3. 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.

  4. 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.

  5. 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.

  6. Why migrate?

  7. Why not migrate?

  8. Migration: how? Two components:

    Mechanism may include:

    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:

Western Grebe
Pied-billed Grebe
Brown Pelican
Brandt's Cormorant
Double-crested Cormorant
Pelagic Cormorant
Sooty Shearwater
Green heron
Common Merganser
Surf Scoter
Turkey Vulture
Red-tailed Hawk
Red-shouldered Hawk
American Coot
California Quail
Western Gull
California Gull
Heermann's Gull
Caspian Tern
Elegant Tern
Mourning Dove
Anna's Hummingbird
Acorn Woodpecker
Hairy Woodpecker
Black Phoebe
Ash-throated Flycatcher
Pacific-slope Flycatcher
Violet-green Swallow
Barn Swallow
Cliff Swallow
Purple Martin
Steller's Jay
Western Scrub-Jay
American Crow
Chestnut-backed Chickadee
Bewick's Wren
Wison's Warbler
Spotted Towhee
California Towhee
Dark-eyed Junco
Brewer's Blackbird
Song Sparrow
Black-headed Grosbeak
Purple Finch

9. Communication and nesting

Communication through:

  1. Posture.
  2. Plumage.
  3. Sounds. Only birds, humans, and dolphins have developed complex communication sounds. Vocal bird sounds are songs and calls. Non-vocals sounds included percussive tapping with beak, feet scuffling, wings.

No physical difference in how songs and calls are made. Main comparisons:

Songs Calls
Long Short
Complex: lots of notes and melodies Simple
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:

  1. Alarm.
  2. Attract prey by mimicking it.
  3. Begging: e.g. chicks.
  4. Contact: keeps a feeding flock together during feeding (e.g. chickadee) or a traveling flock together during migration.
  5. Defend feeding territory (as opposed to breeding territory, which is defended by song).
  6. Distress: "get out of here, it's not safe", such as starling.
  7. 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.
  8. Mimic predator.
  9. Rally: "come and help", such as a crow or raven threatened by a hawk and calling for a mob.
  10. Threats (such as gull's "go away" call).

Creation of bird sound:

  1. Sirynx: two paired passages containing vocal chords at bottom end of trachea. Can make more than one sound at once.

  2. Birds use about 100% of air to produce sound. Humans use only 5%.

  3. Some birds have no nerve attachments to sirynx and can only grunt.

  4. Loud trumpet or bugle sound of the sandhill cranes; chamber like a horn. a traveling flock together during migration.

  5. 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.

  6. 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.

  7. Vary syntax (melody). How many notes do you use and how do you arrange them?

    species repertoire
    Mocking bird 100-200 songs
    Average 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:

  1. Maintain the species barrier: song as breeding barrier.
  2. Synchronize breeding of males and females.
  3. Establish territory for males and attracts a mate. Sing on the edge of the territory, showing its size.
  4. Through variety of song, suggest experience and health.
  5. 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.
  6. The cost of song diversity is the sacrifice of recognizing one's neighbor.
  7. Best mimics are parrots.

Communication and cognition tested through cognitive tests for recognizing symbols, making connections, showing elasticity in thinking:

  1. Parrots have outperformed dolphins and seals in making leaps of understanding.
  2. Corvids.

Song learning:

  1. Baby bird arrives with a template.
  2. 20-80 days critical learning stage where you have to hear your father or a neighboring male.
  3. Male song crystallizes at about 10 months.

What does a male's song tell a female:

  1. I'm here.
  2. I'm male.
  3. I'm a spotted towhee (or whatever).
  4. I'm available.
  5. I'm in breeding condition.
  6. I'm fit and healthy (how well I sing).
  7. I have a territory.
  8. It is big.
  9. It is good.
  10. It is safe from predators: I am out here singing.
  11. I sing a lot: I am a good provider and don't have to be always foraging.
  12. I'm experienced.
  13. 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.


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. Bird relationships:

  1. Biparental care: When both parents are required for the chick to survive, "obligate" monogamy, e.g. when:
  2. "Facultative" monogamy: One parent could raise the chicks without help, but two parents result in more offspring.
  3. "Lekking":
  4. "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.
  5. Cooperative nesting systems:

"Almost no divorce among successful pairs."

11. Bird conservation, part One

Student presentations on:

  1. Burrowing Owl: range and number reduction. Need 10-or-so hectares (25 acres) of appropriately undisturbed habitat.
  2. 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.
  3. 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.
  4. Clapper Rail: population collapse and partial recovery.
  5. 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.
  6. 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.
  7. Impacts of long-line fishing on albatrosses and gill-net fishing on Common Murre.

12. Bird conservation, part Two

Student presentations on:

  1. Plastic Pollution of the Ocean, particularly its effects on the Albatross.
  2. Wind turbines and avian death.
  3. 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."
  4. Effects of DDT on Bald Eagles and other birds.
  5. Recovery projects of Snowy Plovers and Great Lakes Piping Plovers.
  6. Condor recovery program.
  7. Discovery of the Marbled Murrelets and their subsequent reduction.
  8. The Iwa [thief] or Great Frigate Bird.


Buy 'The Sibley Field Guide to Birds of Western North America'


Buy A Primer of Ecology Buy 'Evolution'

The Ecology Footprint quiz