Geoscience Reference
In-Depth Information
potential.Thepossibilityofwinningthefossilizationsweepstakesshrankevenmore
if these nests were high up in trees, away from entombing sediments. Not surpris-
ingly,then,sticknestsattributabletonon-avianoraviandinosaurshavenotyetbeen
interpreted from the Mesozoic Era. Much more likely to be preserved are massive
nest mounds, like those made by modern mallee fowls or some of the extinct birds
of New Caledonia.
Nevertheless,eventhoughtracefossilsdonotyettellusexactlywhennon-avi-
anoraviantheropodsfirststartednestingintrees,wedoknowwhentheyboredinto
tree trunks to make cavity nests, like those made today by woodpeckers. At least
onevase-shapedstructuredescribedfromapetrifiedlogfromcentralEurope,dating
from the Miocene Epoch (about 23 to 5
mya
), is remarkably similar to woodpecker
nests. Because this was well after the dinosaurs were gone, and no older ones have
been found yet, this fossil cavity nest implies that the exploitation of tree trunks for
nesting might have been a totally Cenozoic innovation in birds. Yet all we need to
start a goodargument onthat point is a trace fossil ofa Late Cretaceous cavity nest.
Burrows: The Avian Underground
Some birds are impressive burrowers. In my experience, this statement surprises
manypeopleuntilyousaythewords“burrowingowls”(
Athene cunicularia
),which
elicitsbigsmilesandvigorousheadnoddinginappreciationoftheseadorablebirds.
Yet these owls are not the only birds that use burrowing as part of their normal life-
styles. In North America, belted kingfishers (
Megaceryle alcyon
), bank swallows
(
Riparia riparia
), and rough-winged swallows (
Stelgidopteryx serripennis
) burrow
into soft, sandy bluffs adjacent to rivers or other bodies of water for their nesting
and raising of young. In Europe, Africa, and elsewhere in the world, all species of
bee-eatersmakebankburrows,sometimesbythethousandsatnestingsites.TheAt-
lantic puffin (
Fratercula arctica
) of North America digs lengthy burrows, some of
whichare3m(10ft)longand1m(3.3ft)belowthegroundsurface,alargeburrow
for a small bird. Some species of penguins, such as the little penguin (
Eudyptula
