Ever try to follow a bird in the woods? Hard, isn't it.

Cari Lynn getting a radio transmitter ready for deployment. You can see a small antenna and receiver on the table in front of her.
Ever wonder how a person can follow an individual bird through the woods? The truth is, its pretty difficult and there is no real easy way to do other than persistence, laser focus, and a quick eye with binoculars. There, a flash of yellow in the leaves! There it goes! Run! Ok, it landed in that tree over there. Yea, its not easy to chase a flying object through the woods on your own two feet. I know, I have spent hours of my life doing just that. The feeling is a little like chasing a fly around your kitchen with your flyswatter - slow and steady for a bit while you creep up, then boom its gone somewhere else and there you go chasing after. There is technology, however, that can make finding individual birds easier: radio telemetry. This is a very common technique when studying wildlife from cougars to songbirds.

The technique works like this. First you catch the animal, place a radio transmitter (which is powered by a battery) on the animal using either a collar or 'backpack', then let it go! Later, we go back with an antenna and listen for beeping coming from the exact frequency of the radio transmitter on the animal (the antenna looks something like a small version of the antennas people put on their roofs to get free-to-air local TV stations). We can then follow the beeps until we find the animal, and then keep following it! Too easy! Ha, maybe in theory...

In Hawai'i we use radio telemetry to track all the species of songbirds that live in the high elevation forests of Hakalau NWR. We want to find out where these birds move throughout the day and over time. How big is the area they use on a regular basis while raising chicks? Do they use different areas during at times of the year when they are not breeding? Figuring out what areas and resources birds use over the year is important information for people who manage lands and want to conserve these species.

taking pics of an 'Oma'o after banding it - we take pics of all the birds for aging reference later
Step one, putting the transmitter on a bird. In Hakalau we are catching banding birds all the time for other aspects of the research, so when we catch a bird species that we want to track with a transmitter, we simply do it then and there. These transmitters are very small (smaller than my thumbnail) and sit in the middle of the bird's back against the skin. It is held in place by two elastic straps that slip around the bird's legs just a person wearing a little backpack. The straps are designed to break after several weeks so the bird will not have the transmitter on it for terribly long.

An 'Oma'o getting a transmitter put on
'Oma'o size transmitter being tied closed after checking the fit on the bird
That is the easy part. Next comes following the bird in the woods! We have many birds with transmitter on them at the same time, but each transmitter emits a different frequency, allowing us to find a particular individual. To start with you listen for the frequencies of all the birds, and choose an area to go towards where you hear some individuals that you want to track. Then you narrow in on their location by turning the gain up or down in conjunction with the volume on the receiver (the device that picks up the transmitters signal).

Aha! I hear a steady beep from the direction that the bird is, and it gets louder and stronger in signal if I point the antenna I'm holding directly at the bird. Eventually I get close enough that I start looking for the bird with my eyes, knowing it must be somewhere around here. This is where birds like Red-billed Leiothrix become impossible, since you rarely see them. They live in the underbrush and thick bushes of the forest understory. On flipside, birds like I'iwi and 'Apapane are very easy to see - since there are so many of them and they spend all their time feeding on nectar in the tree tops. So the trick is to find the correct individual bird from the the several that are probably bouncing around in the same few trees. The nice thing is we have tags on a lot of male I'iwi, and they like to sing from open perches now that the breeding season has started (and if you looked like they do you would show off too), which makes locating the exact bird you are after much easier, because you can see their bands and the antenna on their back.

I`iwi resting on one leg
While banding, we also tried out a new style of harness for the transmitters, altered slightly so that it can be fitted to each individual before the leg loops are tied off for good. Hopefully this allows us to put the transmitters on more easily, and cuts down on the handling time of birds that don't quite fit a pre-made harness size. Previously some individuals would just be the wrong size for all the harnesses we had made, and we would have to let them go without a transmitter. This research is still ongoing, so we don't have the results yet, but it sure is fun to get to know individual birds in this manner. "I'm going to check on .428, I haven't tracked him in a couple days. Is he still hanging out at the end of Akepa ridge?" And off I go, chasing birds through the woods.

new adjustable, tie off method on an I'iwi


Location: Hakalau Forest National Wildlife Refuge, 60 Nowelo St, Hilo, HI 96720, USA

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