Geoscience Reference
In-Depth Information
and pinning down struggling prey. As a result, many bird species can be identified
from their tracks, which can be further used to interpret their probable lifestyles.
Figuring out which bird made which track, however, does require careful
measurements of footprint lengths and widths, toe lengths and widths, angles
betweentoes,aswellasbasicknowledgeaboutwherebirdsnormallyliveandwhen
certain birds might be in the neighborhood for a visit. For one, I will not be adding
secretary bird ( Sagittarius serpentarius ) tracks to my list of possible track-makers
while doing field work in North America, as this bird is restricted to Africa. Yet
migratory birds, such as sandhill cranes ( Grus canadensis ), might stop by for brief
cameo appearances in places where they typically do not hang out. Hence, people
who track birds also should be aware of which birds are migrating and when.
Bird trackway patterns fall into five behavioral groupings: diagonal walking
(or running), hopping, skipping, standing, and flying. Of course, birds are not ne-
cessarily locked into making just one type of trackway while doing their business.
Robins, for example, are great little runners when on the ground, zipping from one
placetoanotherwhilelookingforearthwormsorotherinvertebratetreats.However,
they can also switch from running to skipping, in which both of their feet leave and
hit the ground at nearly the same time, but with one foot slightly ahead of the other.
(Hoppingdiffersfromskippingbybeingdonewithbothfeettogether,side-by-side.)
Also, just before changing from running to skipping, robins might stop with their
feet next to one another. Moreover, robins are very good at taking off from a stand-
ing start; so paired tracks might be the last ones seen in a trackway. Conversely,
paired tracks might be the first in a robin trackway, telling exactly where a robin
landed. Many a time I have followed a bird trackway and along its length seen such
shifts in its behavior, both understated and overt, recorded all throughout: a script
narratingascenethatisnormallymuchmoredetailedthanifIhadactuallywatched
the bird make the tracks.
Diagonal walking is an easy pattern to understand because it is so similar to
our own walking pattern: right, left, right, and so on, in which a diagonal line can
Search WWH ::




Custom Search