Biology Reference
In-Depth Information
and Southeast Asia, and inland where suitable caves exist. Ittakes about 35days foreach
male to build a nest, constructing a shallow, gluey cup out of strands of saliva containing
predigested seaweed, stuck to the wall of a cave. These nests contain high levels of calci-
um, iron, potassium, and magnesium.
Many sea birds swallow fish so large that several hours after swallowing one, while the
fish head is slowly digesting in the bird's stomach, the tail may still be sticking out the
mouth.
Collectingthemforsoupisbothdifficultanddangerous.Nestcollectorsclimbflexible
rattan ladders dangling from the ceiling of the caves, then inch along bamboo ladders to
gather nests adhering to the roof, as much as 200 feet above the hard cave floor.
Nestsarecollectedtwiceayear.Thefirstcollectiontakesplaceaftertheswiftletshave
built the nests but before laying eggs. The males rebuild, and at this point pairs are al-
lowed to raise their young. After the nestlings fledge and families leave the cave, these
secondnestsarecollected.Swiftletscannotberaisedincaptivityandtheirnestsarefairly
small, making the nests extremely valuable commercially. One pound of “white” nests
(produced by the Edible-nest Swiftlet) can cost almost $1,000, and one pound of “red
blood”nests(whichmaygettheircolorfromtheinsectstheEdible-nestSwiftleteats)can
cost more than $4,000! Black-nest Swiftlet nests aren't as valuable: they get their color
because the bird mixes feathers with the saliva, and the feathers must be removed before
using the nests for soup.
Three of the four North American swifts also use sticky saliva to hold their nests to-
gether and attach them to the walls of chimneys, hollow trees, and other structures, but
theirnestsarehardlyedible,beingconstructedoftwigs,pineneedles,weeds,andsoforth.
The Black Swift uses no saliva at all; its nest is just a shallow cup shaped out of mud or
mosses on seacoast cliffs or behind mountain waterfalls.
Gray Jays have another unusual use for saliva: They coat chunks of food with copious
amounts of saliva before fastening them to trees for storage. Researchers speculate that
the saliva may help hold the food in place and possibly even retard spoilage somewhat.
Q Why do domestic birds such as chickens need grit with their food? Do wild birds
also need grit to help them digest?
