Geoscience Reference
In-Depth Information
insects. Bark peeling from birds can be considerable; I have seen large dead pine
trees ringed by thick piles of bark on the ground, the cumulative work of insect-eat-
ingbirdsandnotjustdecay.Also,seeingthateggsaresuchrichsourcesofnutrition,
beak marks also may be in eggshells of other birds. Yet predatory birds do not just
limitthemselvestoeggsforbreakfast,nordotheynecessarilystickwith“non-avian
only” policies while hunting. Sure signs of bird-on-bird predation are neat piles of
feathers below roost spots, which a raptor plucked while enjoying a once-chirping
treat. These piles may also have the distinctive white fecal sprays of raptors. Of the
preceding traces, though, only the drill holes in trees are likely to have fossilized,
and thus far nothing like these has been interpreted from the geologic record.
Less subtle raptor feeding traces are decapitated bodies of birds, or their coun-
terparts, severed heads. One of the most unnerving predation traces I have ever
seen,belonging toabaldeagle (
Haliaeetus leucocephalus
),wasalongtheshoreline
of a Georgia barrier island. The trace consisted of the isolated head of a laughing
gull (
Leucophaeus altricilla
) that was lying just above the high tide mark. All of
its feathers were still there and its eyes were open, while its neck had been sheared
cleanlyfromitstorso,whichwasnowhereinsight.Notrackswerearoundthehead,
either, which made me wonder if the eagle performed its “Red Queen” impression
whileairborne.Regardless,itwasavividreminderofhowdinosaursarestillkilling
one another, and sometimes in brutally efficient ways.
Dinosaurian Bachelor Pads and Sexy Time
In evolution, not all selection is natural: much of it is sexual. Every second of
every day, mates are chosen or rejected on the basis of whether or not they pos-
sessattractivequalitiestojustifyexchanginggametes.Formales,ensuringthattheir
sperm fertilize females' eggs sometimes means doing more than just looking good,
but also requires more effort, such as courtship. In birds, courtship may involve im-
pressive feats of singing, or flashy displays of feathers combined with dancing, or
showing up rival males in a competition; in other words, not so different from hu-
mans. So as a male, anything that attracts and convinces a female that your genes
