Feeding III: Specialized Structures, Learning

JodyLee Estrada Duek, Ph.D.With assistance from Dr. Gary Ritchison

& PBS’ Life of Birds

Oystercatcher, Nantucket

American woodcock, NantucketGreat Egret

Immokalee, FL

Willet, Nantucket

Crop

• out-pocketing of the esophagus that's particularly well-developed in seed-eaters like pigeons & doves (Columbiformes) and gallinaceous birds (grouse and pheasants)

• specialized for production of 'milk' that pigeons & doves feed to their young. Crop milk is rich in proteins, fats, & vitamins and is produced by proliferation & sloughing off of epithelial cells that line the crop.

Ventriculus or Gizzard

• the avian equivalent of teeth – very muscular (less in birds that eat meat, insects,

nectar, and other 'soft' foods) – used primarily to grind & break up food (such as seeds) – may, in seed-eating birds, contain grit (small stones

ingested to help grind the food) – lined with tough, abrasive keratin-like layer of koilin,

known as the cutica gastrica (or cuticle)The cuticle is secreted by simple tubular glands

Source: http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/herbivores/birds.html

Red Knots & Gizzard Size

Frequency distribution of gizzard mass of free-living Red Knots (N=920).

van Gils et al. (2003) served knots that had large and small gizzards (as determined by ultrasonography) a selection of hard intact molluscs and soft mollusc meat

Knots with large gizzards consumed more molluscs with shells than the birds with smaller gizzards

van Gils et al. (2003) offered a shell-heavy diet, but even the birds with largest gizzards fed 16 hours a day to sustain weight

Birds with smaller gizzards couldn't feed enough. By allowing them to crush more shell per gizzard-full, larger gizzards gave birds the edge

Also found the knot's gizzards enlarged when the molluscs begin shrivelling (as their winter food supply dwindles)

Variable Gizzard Size

• adult Japanese Quail (Coturnix japonica) (a)

• Red Knots (Calidris canutus) (b).

Burrowing owl traps beetles

• Levey et al. (2004) compared what Burrowing Owls ate when there was a typical litter of dung at the entrances to their nest burrows with diet when the dung was removed

• The owls ate 10 times more beetles when dung present; waste did not build up by accident. • Burrowing Owls nest in tunnels, and place a variety of debris, including dung, at entrance • After finding Burrowing Owls had dung beetles in their diet, proposed owls use dung as bait• cleared all nest entrances at two colonies of owls of debris

– one owl colony had a typical littering of dung applied– other was left bare. – after four days each entrance was again completely cleared and the situation was reversed

• when dung was present, the owls ate ten times more dung beetles. • As Levey says, "this experiment demonstrates that tool use makes a difference". --

Peter Wood, BBC News Online

Golf Links Blvd., Tucson

Avian geophagy – purpose?• geophagy (the intentional consumption of soil) is known for geese, parrots, cockatoos, pigeons, cracids,

passeriforms, hornbills, & cassuaries• Brightsmith and Muñoz-Najar (2004) observed ten species of psittacids, three species of columbids, and

two species of cracids consuming soil from banks of a river in Peru. • preferred soils were deficient in particles large enough to aid mechanical breakdown of food• Percent clay content and cation exchange capacity (CEC), both predicted to correlate with adsorption of

toxins, did not differ between used and unused sites as had been found in a similar study• preferred soils were more saline and had higher concentrations of exchangeable sodium• This suggests that the choice of soils at their study site was based primarily on sodium content • Experimental evidence has shown that soils are capable of adsorbing biologically relevant quantities of

toxins in vitro and that soil consumption by parrots does reduce the absorption of toxins in vivo• They did not find evidence that parrots choose soils with greater CEC or clay content, the characteristics

that correlate with the capacity to adsorb toxins• Instead, they found that birds chose soils with higher concentrations of sodium• These two findings are not mutually exclusive but instead suggest that there may be a set of conditional

rules for soil selection• In situations in which sodium concentrations are variable, the birds appear to choose soils that are

highest in sodium (this study)• In areas in which sodium concentrations are uniformly high, birds may choose the soils that have the

largest ability to adsorb dietary toxins

Geophagy in Macaws, Parrots

www.pbs.org/wnet/nature/realmacaw/photoessay6.html

www.pbs.org/wnet/nature/realmacaw/photoessay7.html

A group of green wing and scarlet macaws congregate on a clay lick by a river in the jungles of the Amazon. Clay licks are high concentration of minerals that form in river bank clay deposits.

Below: Parrots at a clay lick.

Bird Diet: Beak & Digestive System Varies Accordingly

• Nectivore• Frugivore• Insectivore• Herbivore – seed-eater• Piscivore• Carnivore• Scavenger• Omnivore

Obligate vs. Opportunistic Practice: • Make a list of 10 birds you think might be obligate

feeders on particular resources. Look at their wings, feet, and beaks. Are they highly specialized?

• Now make a list of birds that appear opportunistic. HINT: They are probably omnivores. Look at their wings, feet, and beaks. How are they adapted for their lifestyle.

• Be sure you consider morphological, physiological, and behavioral adaptations

Food and Learning, Solothe Monarch Butterfly / Jay story

Aposematic colorationMüllerian mimicry

By Lincoln P. Brower

Food and Learning, SocialBlue tits

• blue tit at a bird feeder http://birdcinema.com/view_video.php?viewkey=760c8bbafb4acb29e344

• Blue tits (insectivore & seed eater) and robins learned to drink milk from delivered bottles in 1930s

• When foil covers were introduced, blue tits learned to pierce, socially passed this on; robins never did

http://sunaddict86.blogspot.com/2007/11/provisioning-choices-and-offspring.html

Tool Use• According to reports by Jane Goodall

in Tanzania, vultures search as far as 50 yards from egg to find a proper tool

• forward jerking movement of the vultures' head when breaking an egg with a stone is similar to movement when the bird pecks to break an egg.

• Other species of birds break eggs by throwing them on stones. However, this is not considered tool use because the stone is not being used as an extension of the bird's body.

www.pigeon.psy.tufts.edu/psych26/birds.htm Egyptian vultures

Vulture tool-use hypothesis

• Alcock(1975) theorized vultures originally threw eggs • They evolved from throwing eggs to throwing rocks at eggs. The use of rocks

probably began when a vulture accidentally broke an egg with a rock • Vultures' aim is poor, hitting the target 40-60% ; persist until they succeed • C.R. Thouless (1989) supports Alcock, finding vultures prefer egg-shaped stones• Assumed connection to original behavior of throwing an egg• (National Geographic Society, 1972) showed that vultures will try to use a stone to

break a green or red egg-shaped decoy, but do not attempt to break white cubes • Observations by Thouless of young vultures reared without exposure to adults

proved that throwing stones at eggs is innate, not learned• vultures need to learn that ostrich eggs are a source of food before they begin

cracking them• learning occurs when a young vulture encounters an egg already cracked

Tortoise tossing• In the Dardia Mountains of Greece, eagles can be

seen carrying tortoises up to a great height and dropping them on to rocks below

• The hapless Aeschylus (525-456 BC) (ES-kih-lus ), a father of Greek tragic drama, is said to have met his end this way

• A soothsayer foretold he would be killed on a particular day by a house falling on him; he spent the day outdoors…

• Alas, his bald head looked like a rock

Green Herons Fish with Bait

• The practice of bait-fishing is rare among green herons • The fact that few herons use bait-fishing indicates it is not innate behavior • infrequency suggests the behavior is not culturally transmitted• The roots of using objects to attract fish are unclear• One theory suggests herons imitating human behavior when they use bait for fishing• Attempts to teach herons to use bait for fishing have failed• Another possibility is herons learn to use bait through experience, i.e. the heron accidentally

drops an object in the water and sees the object attract fish• Some researchers believe making the connection between dropping something on the water

and seeing the crowd of fish that results and intentionally dropping bait is very difficult• According to researchers, only exceptionally intelligent herons bait-fish• The intelligence requirement accounts for rarity of green herons who bait-fish• Others argue that infrequency of the behavior is because few herons have the opportunity

to observe the results of dropping an object into the water

www.pigeon.psy.tufts.edu/psych26/birds.htm

The green heron drops a small object onto the waterFish swim to the surface, hoping the object is preyThe heron then snatches the fish

Tool Use

• The Galapagos woodpecker finch snaps off a twig, trims it to size and uses it to pry insects out of bark.

• In captivity, a cactus finch learned to do this by watching the woodpecker finch from its cage. The teacher helped the pupil by passing a ready-made spine across for the cactus finch to use.

Caledonian Crow uses a twig as a tool to extract grubs

Woodpecker Finch

• The finch then drops the cactus spine and holds it under its foot while eating the grub• The cactus spine is carried from branch to branch for reuse• Millikan and Bowman(1967) saw finches adjust posture and manipulation of tool according

to its size and shape• woodpecker finches were more likely to use tools with an increase in hunger • the large Galapagos cactus ground finch was caged next to woodpecker finches; acquired

similar tool usage . Other species of finches did not learn to use tools as probes• observed a young woodpecker finch's acquisition of the skill of using the cactus spine. The

finch attempted to obtain grubs by using its beak. When that failed, it used a twig to reach into the branch. Another finch snapped off a part of a forked twig to fashion a superior tool

• Millikan and Bowman(1967) also observed woodpecker finches shortening long cactus spines to form more manageable tools. This manipulation of an object is impressive

• Brown(1975) posits that woodpecker finches would be replaced by woodpeckers or nuthatches if either of those species were to come to the Galapagos islands. His basis for this theory is that woodpeckers and nuthatches have more effective morphological means for accomplishing what the woodpecker finch does with tools.

www.pigeon.psy.tufts.edu/psych26/birds.htm

A woodpecker's long barbed tongue enables it to extract grubs from branches; the woodpecker finch compensates for its short tongue by grasping a cactus spine in its beak and prying grubs out of the branch with the cactus spine

Carrion Crows

Using Cars as Tools

• Seen in Japan & California since 1990s to crack walnuts• The crows already knew about dropping clams from a

height on the seashore to break them open, but this didn’t work for walnuts because of the soft green outer shell.

www.pbs.org/lifeofbirds/brain/index.html