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PTT STUDY

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Methods
Trapping
Who?
Crane 8725
Crane 8726
Crane 8737
Crane 8746
Crane 8824
Crane 8827

 

 

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:

Up Methods Trapping Who? Crane 8725 Crane 8726 Crane 8737 Crane 8746 Crane 8824 Crane 8827

 


 

 

 

 

 

 

 

 

 

 
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