Trapping
TRAPPING HISTORY
We began trapping attempts on 16 November
2001, but the cranes did not cooperate until they finally started using our bait
sites on 25 November. Trapping was made difficult by their erratic use of
wetland sites: heavy rain caused rising water levels and shifting of roost and
wetland feeding areas, and hunting disturbance forced birds to abandon their
primary Bachelor Island roost when goose season started on 21 November. In
addition, the cranes did not feed in the same grain fields
regularly, and there was disruption of birds feeding on the bait by bald eagles
(Haliaeetus
leucocephalus),
coyotes (Canis
latrans),
and low-flying airplanes. Trapping was also often effected
by capture of non-target species. We caught 9 Canada geese (Branta
canadensis) (3 cacklers and 6
duskys) and 4 mallards. Capture of these waterfowl
occurred when we had cranes near the traps and ruined our chances of catching
cranes during those times. Waterfowl appeared less wary of the lines and were
much more readily captured by this technique than cranes.
The
first bird we captured was a dusky Canada goose in a wetland on 25 November
which disrupted the feeding cranes. On 26 November, we set the lines in a
cornfield where cranes had begun feeding on our bait, and caught a cackling
Canada goose in the morning when cranes were also on the bait. Finally, in the
early afternoon, we caught our first crane (8824). We set the lines at the same
site on 26 November and caught 2 cackling Canada geese in the morning. The
cranes returned to our bait without the company of geese at
about 11 AM, and we caught our second crane (8726). We assessed the situation,
and because we did not observe any lessers, we decided to return in the spring
to increase our chances of capturing California migrants and lessers.
We resumed trapping in late February 2002.
Caroline Herziger arrived at Ridgefield NWR on 25 February, and scouted out a
corn field cranes were using and baited a trap site. Gary Ivey appeared on the
evening of the 26th and we began trapping the next day. After
catching a dusky Canada goose in the morning, we caught a third crane in the
early afternoon (8827) and attached another PTT. We decided to postpone further
trapping until March in hopes of catching migrants, however, we had
Oregon Field Guide scheduled to film and discuss the project on the
28th, so we reset our noose line traps and captured a fourth crane on the 28th
with cameras rolling. We marked and banded this bird, but did not apply a PTT.
We returned to Ridgefield on March 8 to find
that almost all of the cranes had abandoned the area and were using Sauvie
Island WA. The staff at Sauvie Island had recently mowed most of their
unharvested corn fields, and there were at least
1,500 cranes using the island. We had to wait to trap at Sauvie until we could
get an Oregon banding permit from Oregon Department of Fish & Wildlife on Monday
the 11th, so we spent the weekend scouting for the best trapping location. On
Tuesday, we set our traps near the Stutzer Barn on
the WA, and by 8 AM caught 2 birds at the same time in one line. They, like the
other birds that we had captured, both appeared to be Canadians. We put a PTT
radio on the smallest of the two (8725) and marked and banded the other. We
reset the traps, and while Caroline monitored the site, Gary took a hand-held
radio to stay in touch, and spent time looking at as many cranes as possible to
determine whether there were any lessers in the area. There were a few smaller
birds in the flocks, but their heads had the same shape as the Canadians they
were with, and the bill was equally as long. At about noon we caught a third
crane which was much smaller than any of the other birds we had handled (8737).
So, we decided to fit it with our fifth PTT. Some of its measurements keyed it
out as a lesser, but its weight, wing chord and exposed culmen (bill length)
measurements overlapped with those for Canadians. Its head was also shaped like
the other Canadians, and we suspected that it was a small Canadian. Later that
afternoon, we caught another dusky Canada goose.
We decided to delay trapping
again, returning on March 26, and again we found most
of the cranes using Sauvie Island. They were feeding mostly by digging, and we
presumed they were hunting earthworms, but Sauvie Island WA manager Mark
Nebecker informed us that they were likely digging for nut sedge (Cyperus
esculentus)
tubers, a food that cranes really like. At this point they were not very
interested in our corn bait. We finally caught our last crane on 4 April (8746,
the sixth and final PTT and the eighth bird captured). It too measured as a
Canadian.
Click the following items to see detailed results for this study: