Biology Reference
In-Depth Information
Swallows, Tree and Violet-green (nest box — same size as for bluebirds)
Wood Duck (nest box)
Wrens (nest box or nest tube)
The Family Life of Birds
Q Birds seem so devoted to one another, courting and raising their young together.
How many species mate for life?
A
There is a great deal of variation among species, and even among individuals, with re-
gard to mating systems. Swans, geese, and cranes may migrate long distances between
nesting and wintering grounds, pairs remaining together throughout. Eagles and falcons
may also migrate long distances and nest with the same partner year after year, but there
is little or no evidence that they remain together except during the breeding season.
FloridaScrub-Jaysarenottheleastbitmigratory—birdsspendtheirentireliveswith-
in a very small area — and pairs remain together as long as they both survive. Trop-
ical wrens that remain on the same territory throughout the year not only mate for life
but learn to sing complex duets, some so perfectly synchronized that it may sound like a
single bird unless the listener stands between them.
There may be some randomness about other birds pairing for life. Chickadees tend to
select mates from across the dominance hierarchy within their winter flock: the highest-
ranking female mates with the highest-ranking male, the second-most dominant female
withthesecond-mostdominantmale,andsoon.Flocksarefairlystablefromyeartoyear,
so some of these pairings may last several years. But when a high-ranking bird of one
sex dies and the rankings shift upward, a shift in pairings usually occurs. Some birds that
return to the same general nesting area year after year can end up with the same mate.
With robins, this tends to occur more often when they were successful raising young the
previousyear.Andformanyspecies,thereislittleornotendencytoselectthesamemate
in subsequent years.
Many species remain together for an entire season, but some only remain together for
a single nesting and then both birds find new mates. After a pair of House Wrens fledges
abrood,thefemaleoftenfindsanewmatewhilethemalecontinuestorearthefledglings
and attracts a new mate. In contrast, many ducks remain together during nest-building
and egg-laying, but then males move on when the female starts incubating.
Some species don't remain together for long. Ruby-throated Hummingbirds don't
formapairbondatall.Themalecontributestothesurvivaloftheyoungbydrivingaway
other birds and many large insects from nearby flowers, ensuring that the nectar supply
