Feeding II: Tongue, Taste

JodyLee Estrada Duek, Ph.D.

Feet and talons • Some hawks and owls use feet and talons• raptor prey are killed by the talons of the

contracting foot being driven into their bodies • hooked bill is used to kill prey being held by the

talons (check this short video of an owl trying to eat a moth).

• Feet used to help with a meal of Ostrich egg http://video.nationalgeographic.com/video/player/animals/birds-animals/birds-of-prey/vulture_egyptian_ostrichegg.html

Talons of (left > right): Harpy Eagle, Golden Eagle, Bald Eagle, Great Horned Owl, Red-tailed Hawk, & Peregrine Falcon

Bristles • stiff and hairlike, consisting of a central rachis without vanes, and

provide both protective and sensory functions• occur most prominently around the eyes ("eyelashes"), the lores, the

nostrils, and around the rictus (corners) of the mouth• Rictal bristles are prominent in many insectivorous birds, particularly

aerial insectivores like nightjars (Order Caprimulgiformes) and flycatchers (Family Tyrannidae)

• may be used as sensory organs to help locate and capture prey, much like mammals use whiskers

• bristles around the mouth may help protect the eyes from food items a bird is trying to capture (Conover and Miller 1980) rictal bristles of a Hooded Warbler

Tongue• can aid in gathering and swallowing food • usually not very muscular; aided by hyoid apparatus • morphology varies with food habits: – Fish-eaters - typically small, undifferentiated tongue

because fish are often swallowed whole – Woodpeckers - the tongue is long, extensible, & 'barbed'

at the tip to facilitate the capture and extraction of prey (like insect larvae) from bark crevices (check this skull of a Golden-fronted Woodpecker).

WoodpeckerSource: http://www.birdersworld.com/AmazingBirds/1995/9504_woodpecker.html

Detailed view of the horny tip (right) of the Guadeloupe Woodpecker tongue in vivo position (Villard and Cuisin 2004).

• Nectar feeders (hummingbirds, sunbirds, spiderhunters, & honeycreepers) - tongues may form an elongated 'tube' allowing nectar to be gathered by capillary action (not by suction)

• may have brushy tips that 'collect' nectar and permit the bird to essentially lap it up

Hummingbird

Source: http://www.zoobooks.com/newFrontPage/animals/virtualZoo/animals/h/humingbirds/head2.htm

Energy and nitrogen balance in a hummingbird I • hummingbirds supplement nectar intake with tiny arthropods.• high metabolic price; flies don't sit still: hummingbirds work hard chasing protein. • Lopez-Calleja used nitrogen laced nectar and found that although their protein

requirements were relatively meager, the tiny creatures' metabolic demands were colossal: 43 kJ day-1!

• López-Calleja et al. (2003) trapped about 40 Green-backed Firecrowns in Chile• Used nectar solutions with different concentrations of amino acids to see how

much protein the birds needed to maintain a stable body weight• By filming the birds as they sipped, they measured the amount of energy and

nitrogen that the birds consumed

Calliope hummingbirdSWRS, Chiricahua Mts., AZ

Energy and nitrogen balance in a hummingbird II• To calculate nitrogen uptake, they also needed to know waste nitrogen

– collected feces, making sure that none dried out, and measured the nitrogen content. – birds fed small amounts of protein began losing weight quickly, even though they were able to sip

as much high-energy nectar as they wanted– birds fed 1.82% nitrogen or more, held their weight. López-Calleja et al. (2003) calculated need at

least 10 mg nitrogen per day

• provided 500 fruit flies to snack on while offering either an unlimited nectar supply, a restricted nectar intake, or no nectar at all.

• After five days of free access to flies and nectar, birds were fit and healthy, catching around 150 flies a day, sufficient to supply them with 5% nitrogen.

• birds with reduced nectar supply also maintained a stable weight, although they went into torpor overnight to conserve energy

• birds fed flies alone began losing weight, no matter how hard they worked to feed themselves

• Fernández, one of the co-authors was surprised that `flies are not a complete food source for hummingbirds'. She suspects that although the flies should supply all of the hummingbirds needs, the birds simply have to work too hard to catch flies to rely on them as their soul food source. -- Kathryn Phillips, Journal of Experimental Biology

Buccal, or oral, cavity

• contains few mucous glands & taste buds • salivary glands well-developed in many birds. – woodpeckers: 'sticky' saliva aids in capturing prey– swifts: saliva is used in nest building

• salivary glands reduced in aquatic species: aquatic prey like fish require little additional lubrication

• Few have “taste” as we know it

Anatomy of a Pepper

Capsaicin Compounds

Name Code Systematic Name

Capsaicin C trans-8-methyl-N-vanillyl-6

Dihydrocapsaicin DHC trans-8-methyl-N-vanillyl-6-nonenamide

Nordihydro-capsaicin

NDHC 7-methyl-N-vanillyl-octamide

Homodihydro-capsaicin

HDHC 9-methyl-N-vanillyl-decamide

Homocapsaicin HC trans-9-methyl-N-vanillyl-7-decenamide

Anatomy of a Capsaicin Molecule

Capsaicinoids are vanillamides of monocarboxylic acids with varying chain lengths, varying degrees of unsaturation

Close Relatives: The Vanilloids

• Distinctive flavors, similar structures• All have 6-sided benzene ring• Size, position of -R change flavor, properties

The Vanilloids

Molecule MolecularWt/Volatility

Solubilityin water,oils

Other

Vanillin(vanillaorchid, ligninin oak)

low / high water presence inlignin - flavorin aged wine

Eugenol(bay, cloves,allspice)

medium / high low in water,high in oils

analgesic,antiseptic

Zingerone(ginger,mustard oil)

high / low low in water,high in oils

antioxidant

Capsaicin(peppers,oregano,cinnamon,cilantro)

high / very low almostinsoluble inwater, high inoils, alcohols

blocksneurotransmitters, releasesendorphins

Amide group (-NHCO-)

Plant Point-of-View: Why make Capsaicin?

• Seeds are for reproduction• Fruits are for attracting animals– They eat the fruit & digest it– They do not digest the proteinaceous seed coat– They deposit seed and fertilizer in new location

• Peppers: birds don’t digest seed coat, mammals do• Plant wants fruit eaten by birds, not mammals• Capsaicin “burns” in mammal mouth

Directed deterrence

• Evolutionary biologist Dan Janson proposed in the late 1960s that plants may use chemicals to deter some animals, selecting preferred seed distributors.

• Known as “directed deterrence,” this theory received little attention and was never observed in nature, and it gathered dust in scholarly journals until Tewksbury and Nabhan decided to see if it might hold true in chili peppers.

Curve-billed Thrasher

Chiltepine studies -- Tewksbury and Nabhan, 2001

• Using video discovered birds — esp. curve-billed thrasher — were only animals eating it• pack rats and cactus mice, the dominant fruit- or seed-eating mammals, avoided entirely• needed to prove that the rats and mice were avoiding the capsaicin • they found a pepper similar in size, shape and nutritional content to capscium annum — but

because of a genetic quirk, the pepper, a variety of Capsicum chacoense, lacks capsaicin• fed this “spiceless” pepper to packrats, mice and birds in labs. All gobbled it up• swapped the hot pepper with the spiceless pepper

– birds continued to eat the pepper– rodents refused to even nibble

• Analyzing droppings and feces showed– birds passed the seeds whole and capable of germinating – rodents, however, chewed up most of the seeds, any that remained were too damaged to germinate

• Tewksbury and Nabhan also discovered curve-billed thrashers spent a lot of time on fruiting shrubs, frequently releasing droppings there. The peppers grew much better in the shade of the shrubs than open desert. The chilies also get two additional advantages: – Birds are more likely to eat the pepper from chili bushes growing near the shrubs, further dispersing the seed– an insect that kills the seeds and fruit of the pepper was much less common in the shade of the shrubs.