Monday, December 10, 2012

4N

Rigby and I are back in Santa Cruz, adjusting to things we haven't seen in a while-- stoplights, traffic, and sunshine, just to name a few. We've finally managed to get internet up and running in our new place, so it's back to blogging!

Today's entry focuses on one of the more frustrating aspects of working with wild animals: data loss. So far, we've been getting pretty reliable information from the GPS tags on our eagles, but the data are not without problems. Since the tags are solar powered, they need to have reliable sunshine to keep the battery charged and the device functioning. In southeast Alaska, where snow is a daily occurrence and daylight hours are rapidly diminishing, it's tough for the tags to get the juice they need. This is complicated by the fact that the Chilkat River is surrounded on both sides by relatively steep mountain ranges. Even when the sun does come out, much of the river is still in shadow.

Although we do lose data points to lack of battery power, we've been able to keep relatively close tabs on all five of our birds. We see where they move from day to day, the directions they take while flying, and even where they perch overnight. We can also see when they stop moving.

A couple weeks ago, we noticed the data points on 4N, one of our two adult females, were very highly clustered in one location. We thought initially that she could be on a good food source and was perhaps just not moving around much, but the next series of points we received confirmed that she (or the tag, at least) had stopped moving. This could mean one of two things: either the tag fell off (the harness broke, or 4N managed to cut through the Teflon ribbon), or 4N has died.

Unfortunately, unless we can locate the tag, it will be difficult to determine exactly what happened. Even though we have GPS locations pinpointing the area the tag is most likely to be, finding a four inch long tag in a river valley is a lot like finding the veritable needle in a haystack. It would be great if Taal and Jenn (who are still in Alaska) could simply walk out to the last location we received from the tag and pick it up. The tag, however, is on the south side of the Chilkat, opposite from the Haines Highway, and is difficult to access, especially with much of the river frozen or in the process of freezing. The ice is too thick to boat through, but much too thin to walk across. Add in three or more feet of fresh snow, and more falling every day, and needles in haystacks really have nothing on a GPS tag in the Chilkat Valley.

4N's GPS points, near Klukwan, AK. The tightly clustered points over several days suggest the tag is no longer moving around-- either 4N has died or the tag has come off.
Taal and Jenn will try their best over the coming few days to locate the tag. If they can't manage to find it in the snow, we'll have to try again, maybe as late as next July when I make my next trip to Haines. If we recover the tag, we can reuse it. If we recover it quickly enough, we might have a chance to figure out just what happened. Did 4N die, or did the tag fall off? If she did die, are there any indications-- injuries, eagle pox, etc.-- as to why?

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