This morning, after months of invitations that I could not accept due to teaching commitments, I was finally able to join a group of folks at the Younger Lagoon Reserve (YLR) for their weekly bird banding activities. During the summer months they start early, trying to catch birds in the few hours after dawn. I didn't get out there until almost 07:00, and they had been "fishing" for about 45 minutes already. They were finishing up the process with a Wilson's warbler and went out to release the bird as I came up.
Bird banding activities are overseen by a person who holds state and federal permits to work with birds. The permit holder for the Younger Lagoon Reserve and the Fort Ord Natural Reserve is Breck Tyler. Either he or his partner, Martha, must be on site whenever birds are being banded. The other regular participants are YLR staff members Vaughan Williams (Restoration Field Manager), Kyla Roessler (Assistant Restoration Steward), and various UCSC undergrads who are interns, volunteers, or students visiting with classes. Back in March I brought my Ecology students to YLR to observe bird banding and work on vegetation restoration in the Reserve's terrace lands; on that day we did help with planting, but got skunked on birds.
When I arrived this morning it was sunny and cool. Vaughan told me that the best weather for bird banding is one of the overcast, foggy mornings that we often get in the summer. When it's sunny, like it was today, the birds can see and avoid the nets.
The mist nets are made of an extremely fine nylon mesh. They are very loose and flexible and don't hurt the birds. A bird flies into the net and gets tangled in it. If the bird is heavy enough, it and the mesh it is tangled in fall into one of the pockets of the net. The banders check the nets about every 20 minutes, so a bird isn't tangled for very long. At the end of the morning the nets are taken down and put away so they aren't a hazard to birds. In addition to the nets, the banders set traps at ground level. The traps are kept in place all the time and are baited with seed so the birds know they can get food there. During a banding session the trap doors are allowed to shut on a critter that ventures inside, but at other times the doors are clamped open so animals can wander in and out. This morning we caught a vole in one of the traps. I didn't get to see it because I was with the group of people checking the nets.
But the first bird I got to see was caught in a trap! It was a California scrub jay (Aphelocoma californica) that had clenched its feet around the wire of the cage, making for a difficult extraction. Sophie, the intern wrangling this particular bird, had quite a job of it.
The bird, once extracted from either net or trap, gets put into a cloth bag and taken to an area called The Yard to be worked up. Each bird gets the following treatment:
- A complete formal ID, which can be really easy or really difficult
- Banded on the left leg with a unique number
- Sexed, if possible
- Aged and life history stage determined. Age can be guesstimated by examining patterns of wear on the feathers. Missing feathers can indicate either a molt or some recent mishap in the bird's life. Some species are not sexually dimorphic, but females that are incubating or brooding have a patch of bare skin on the front underneath the feathers. Our scrub jay had a brood patch and is thus a girl!
- Measured and weighed
The banding itself has to be done by either Martha or Breck. They are the ones with the training required to squeeze tiny bracelets around skinny legs.
It takes practice and skill to hold a bird immobilized but still able to breathe. You also have to avoid the feet, which are equipped with sharp talons. Elizabeth, the intern to whom Martha relinquished this bird for the remainder of the workup, neatly solved the problem of the feet by giving the jay a bag to hold onto. The bird's left leg, wearing the band, is tightly clenched and the right one is grasping the bag.
To examine the skin the handler blows up the feathers. To me this was surprisingly effective. I sort of assumed the bird's down feathers would be too thick to blow through. A good puff blows the feathers up and uncovers the skin.
Birds the size of jays are weighed in bags hung from a spring scale. The scrub jay in its bag weighed 90 grams. The empty bag weighed 15 grams, so the bird's body weight was 75 grams. The weighing was the last part of the workup, and after that she was released. Birds with an active brood patch are probably tending eggs or babies, and should be released in the area where they were caught so they don't have to expend a lot of energy flying back to the nest.
In addition to the scrub jay, we also caught a bushtit and a Bewick's wren. Bushtits can be problematic because they flit around in large flocks, and sometimes 20 or 30 of them will fly into the nets all at once. This results in a frenzy of activity for the banders, who want to work up the birds quickly so they aren't overly stressed. Breck said that while the data are important, the birds are more important, and if they have to let birds go without working them up, then they will. Bushtits are tiny birds--look at how small that wing is!
The last bird we caught was a Bewick's wren (Thryomanes bewickii). These little birds have a reputation of getting pretty tangled in the nets, because when they hit the mesh they start thrashing and making things worse. When I went out with Elizabeth to check the nets we saw the wren wrapped up in the net. It took Martha's expertise to get the bird free, and it screamed the whole time. That's a good sign, as a bird that complains is a bird that is angry rather than scared. Sometimes the net needs to be cut to free the bird, but this time patience and expertise were all it took.
A Bewick's wren is more substantial than a bushtit, although not by much. And it has a tiny leg that requires a tiny band.
And the coolest thing is how they weigh these teensy birds. They're so small that they can fly around inside the bag, which means they aren't confined and would be unlikely to hold still long enough to get an accurate weight measurement from the spring scale. But years ago there was a company named Kodak that manufactured and sold millions of small plastic canisters that probably make up a significant proportion of landfill materials around the world. These little plastic containers happen to be the perfect size for containing the head half of a wren-sized bird, keeping the bird calm so it can be weighed.
Worked like a charm!