Feeding I: Overview & Beak

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

http://people.eku.edu/ritchisong/avian_biology.htm

Because of their high metabolic rates• Birds must consume more food in proportion to their size than

most animals. – a warbler might eat 80 percent of its body weight in a day. – birds consume just about any type of food: amphibians, ants, buds,

carrion, crustaceans, fish, fruit, grass, insects, larvae, leaves, molluscs, nectar, other birds, pollen, reptiles, rodents, roots, sap, seeds, suet, snails, wax, & worms

• To meet their metabolic needs while remaining as light as possible (to be efficient flyers), the digestive system of birds has to be – light as possible– efficient as possible

• Weight has been minimized by– loss of teeth – limited jaw musculature.

http://www.nps.gov/cebr/naturescience/images/Orange-crowned_Warbler.jpg

Efficient Feeders

• Must keep weight as low as possible• Limited amount of fat can be stored– except perhaps prior to migration

• 'Efficient' means birds locate, ingest, & digest food quickly and efficiently

• Next slide: Retention time (in hours) for fluid & particulate digesta markers in gastrointestinal tracts of representative reptiles, birds, & mammals (Stevens & Hume 1998)

Magnificent hummingbird, SWRS, Chiricahua Mtns., AZ

In general, typical mean retention times are 30 - 50 minutes for avian nectarivores, 40 - 100 minutes for granivores, and 15 - 60 minutes for frugivores

(Karasov 1990, Klasing 1998).

Species Body massFluid retention

time (hr) Particle retention

time (hr)

Iguana - <48 207

Broad-tailed Hummingbird1

3.3 gm 1.2 -

Rock Ptarmigan 460 gm 9.9 1.9

Sooty Albatross 2.5 kg 6.3 15

Rockhopper Penguin

2.5 kg 3.8 17

Emu 38 kg 3.9 4.7

rabbit 2.1kg 39 27

pig 176 kg 39 48

Typical Avian

Digestive System

Source: http://numbat.murdoch.edu.au/Anatomy/avian/fig4.1.GIF

A bird's bill

• consists of a bony framework • covered by tough layer of keratin• keratin layer continuously worn down by eating and

manipulating hard objects• keratin layer continuously replaced• cutting edges of the beak: tomia • critical in food acquisition, shape varies with food

http://www.bbc.co.uk/tyne/content/image_galleries/northumbria_icons_farne_puffin_gallery.shtml

http://www.tropicalbirding.com/tripReports/TR_NorthernAndesEcuador_Jan07/tripreportnorthernandesjan07.htm

Bill examples• Flamingos use a series of projections, or lamellae, to filter tiny food items from debris in the

water. • Swifts are aerial insectivores & use their wide gape to help capture flying insects. • Eagles (and hawks) are diurnal raptors & use their hook-like bills to tear apart large prey.• Shovelers use their spatula-shaped bills to filter food from mud & water. • Crossbills use their 'crossed-bill' to extract seeds from pine cones. • Herons use their bills to spear small fish and amphibians.• Avocets sweep their long

up-curved bills from side-to-side through the water to capture small invertebrates (or use it like a forceps to pick up prey).

• Woodpeckers use their chisel-like bills to chop away wood & expose insects and insect larvae.

• Wrens use their thin, probing bill to capture small insects. • Curlews use their long bill to probe mudflats for small invertebrates. • Hawfinches are seed-eaters & use their bills to crack open large, hard seeds. • Macaws use their strong hook-like bills to feed on nuts. • Mallards & other waterfowl use their bills to filter small invertebrates from mud and water. • Skimmers use their elongated lower mandible to skim the surface of the water & capture

small fish and invertebrates.

A kingfisher capturing prey!

Toucan beak

Toucan beak• outer shell is hexagonal keratin tiles cemented together

with organic glue and piled in several staggered layers• The interior is rigid "foam" composed of bony fibers and

drum-like membranes sandwiched between outer layers of keratin

• The "foam" is covered with overlapping keratin tiles, each about 50 µm in diameter and 1 µm thick, glued together to form sheets. The closed, air-filled spaces reduce overall weight without loss of rigidity.

Bill

• A bony framework covered by a tough layer of keratin

• keratin layer is continuously replaced throughout the life of a bird & is just as continuously worn down by eating and manipulating hard objects

• cutting edges of the beak are the tomia

• The bill plays a critical role in food acquisition &, of course, bill morphology varies with food habits

Finch eating seeds• lower mandible is

moved toward the tip of the bill in a slicing motion.

• When most of the coat has been cracked or removed, the lower mandible is moved from side to side to remove the rest of the shell, releasing the kernel

Hummingbird catching insects• Hummingbirds have bendy

lower beaks to help them catch insects (Yanega and Rubega 2004).

• The flexibility allows long-beaked birds to open their mouths wide enough to hunt on the wing.

• Hummingbirds use their long, narrow beaks to probe flowers for nectar, but they also need insects for essential nutrients.

• birds that hunt flying insects usually have short beaks to help them open their mouths wide. - Helen R. Pilcher, Nature Science Update

Cape Gannet Capturing Prey

Photo source: http://www.homepages.mcb.net/wormwell/Gannet130604.htm

plummeting from up to 30 m into the water, where they seize fish with their razor-sharp beaks. Ropert-Coudert et al. (2004)

Kingfisher

• http://ww3.osf.co.uk/ftg_runclip.html?clip_id=9348&file_type_id=2 from above

• http://www.youtube.com/watch?v=kgrRD4ono6k from below

• Hyacinth Macaw eating palm nuts http://www.youtube.com/watch?v=NLh6u587I8E

• Black Skimmers http://www.youtube.com/watch?v=5Q8unR8XEZQ

• Red-tailed Hawk eating a Red Squirrel (graphic!) http://www.youtube.com/watch?v=lNnrb5sX6uk

• Foraging Wilson's Petrels The Bird That Walks On Water - video powered by Metacafe

• Pale-billed Woodpecker (Mayflower Bocawina National Park, Belize) http://www.youtube.com/watch?v=iwFOmwBXHmo

• Vultures move in on lion kill: Video• Cory’s Shearwaters & Common Dolphins http://www.youtube.com/watch?v=ozTlQzzw-8A

• Red-necked Phalarope http://birdcinema.com/view_video.php?viewkey=feedfdeaab192ead4ac0

Birds Feeding