Biology Reference
In-Depth Information
won't be depleted when the larger, dominant female flies in to feed. This minimizes the
amount of time she must spend away from eggs and chicks.
Malegallinaceousbirds,suchasturkeysandprairie-chickens,produceadisplaywhich
attracts females. The most successful males may mate with many females. The females
nest and care for the young without male assistance. In some cases, such as in turkeys,
themalesmostlikelytobeselected asmatesarealsothemostaggressive, andsofemales
must try to keep their young ones away from these males until the young can protect
themselves.
Whether birds of a pair stay together for a lifetime or for a nest period, there is also a
great deal of variation in whether birds mate with birds other than their social partners.
Ornithologists used to believe that the vast majority of bird pairs were faithful during a
nesting, but DNA tests have revealed that more than one male has fathered many broods
in more than 90percent ofall species tested. “Extra-pair paternity” is extremely common
in ducks and some swallows, but extremely rare in Florida Scrub-Jays.
Teasingoutthereasonswhydifferentspecies,sometimescloselyrelated,haveentirely
different mating systems can keep amateur and professional ornithologists engaged for
years.
Q Many species of birds share parenting duties after the eggs hatch. Do males help
with the incubating process?
A
Insomespeciesyes,andinothersno.MaleandfemaleRose-breasted Grosbeaksshare
incubation duties. Some male Barn Swallows incubate a great deal and others don't, and
only the males that do incubate develop a
brood patch
— a bare spot on the belly where
the heat of the adult is transferred to the eggs. Loons take turns during the day but only
the female incubates at night. Woodpeckers take turns during the day but only the male
incubates at night.
In some species, such as hawks, owls, jays, and crows, the male hunts and brings food
tothefemale,whoremainsonthenestvirtuallyallthetime,especiallyduringbadweath-
er. In some shorebirds, especially phalaropes (delicate birds that spin like tops as they
swim tostir upfood),onlythe male incubates andcares forthe babies. Inthese cases, the
female is the one who defends the territory.
There are almost as many reasons for differences among incubation strategies as there
are species. Sandhill Crane females incubate while males guard. In the unrelated but su-
perficially similar-looking Great Blue Heron, both sexes develop a brood patch and both
take turns incubating.
Hummingbird and raptor females are larger than males, and in both groups the female
incubates. But relative size cannot be the explanation because in geese and most black-
birds, the male is significantly larger than the female, yet again the female is the one who
