Tuesday, July 03, 2012

The Sharp End of a Goshawk

Talons of a nestling Northern Goshawk.

Welcome to the latest update from my field season studying the Northern Goshawk in the Sawtooth National Forest covering weeks 6 & 7 of my season. It is hard to believe the season is nearly over. Just one full week remaining followed by a short visit a few weeks later. This bout had a great deal of progress to report on, so sit back and enjoy the story.

Previous field updates

Week 1: Oh, What a Great First Week it has Been
Week 2 & 3: As Slow as Possible, As Fast as Necessary
Week 4 & 5: Intimate Encounters with a Northern Goshawk
Week 5: Charlie's First Meal After Returning Home

The project has shifted from performing a lot of surveys and searching for nests, into more extensive monitoring of the individual nests. While we are still searching for nests and performing some prey surveys, this bout of effort was much more focused on the nestlings themselves.

Before getting to the details of our nestling activities, I am happy to report a few significant items that we accomplished this week. First of all, we discovered three more additional occupied nests for a season total of 17. I only had ten last year and two of those had failed by this point in time. Nestlings have hatched in all 17 territories and there have been no nest failures. Hmm, its hard to analyze the factors influencing success/failure rates with no failures... However, this is not a problem that I am going to complain about!

A second great discovery is that I was able to read the band number on the only sub-adult female (1 year old bird) that we have found breeding in the area. Usually females don't breed until they are full adults (2 years old). She was one of the birds that I banded last year as a nestling. I was hoping that it would be "Chuck", but I will accept that "Chuck" is still roaming the skies somewhere and that one of my other banded nestlings is successfully raising her first offspring in this nest.

Half of our effort over the past few weeks has been climbing trees, banding young, and extracting blood samples. The banding process helps us to better understand the dynamics of this population of birds. Is this population of goshawks a population sink (net-negative contribution to the regional population), or a source (net-positive contribution). In the past year we have three new datapoints from banding activities which will help answer this question (including the sub-adult female that I just mentioned). The blood samples are collected for two purposes. The first use is to evaluate the nestlings for Leucocytozoan infection. It has long been hypothesized that the goshawk population suffers from infection by this parasite and that the parasite is having a significant impact on the population by killing the offspring. The parasite is transmitted by Black Flies which are abundant in the South Hills and abundant within the goshawk nests. An undergraduate student, Michelle J, will be heading up this investigation in conjunction with my project. The second use of the blood will be for a yet-unidentified undergraduate researcher to evaluate the genetic diversity of the population for signs of inbreeding depression. A previous study in Arizona found that the genetic diversity is higher there than would be expected given the population size. We would hope for a similar result in the South Hills as the South Hills population, while large, is not large enough to ensure the long term survival without immigration of genetic diversity.

I'm heading up the first of nine nests we processed this week, using the spur and sling approach.

The process may seem simple, but a full team effort is required to successfully climb the trees and keep the birds and the climbers as safe as possible. The first task is for the climber to get up the tree. We generally climb using spurs and then rappel out of the tree. However, we occasionally have "shot a line" through the upper branches of the tree to pull a rope up and climb the rope. If feasible, this method is faster, generally safer, and has a lesser impact on the tree. Unfortunately, on the first few climbs I had to "down-climb" as there were no good rappel anchors.

I arrived at the nest within 4 minutes!

After the climber arrives at the nest, a bag is attached to the rope to transport the nestlings. An elastic sock is placed over the bird to hold the wings in and keep it safe. Sometimes a hood is also placed over the bird's head to decrease stress. The bird is placed into the bag and slowly lowered to the ground.

Mike receives first bird on the ground.

Once on the ground the bird has two bands applied - a silver 9 digit USGS bird band and a Purple color band with a two digit code. The color band allows for remote identification of the bird with binoculars without the requirement to recapture the bird. This is how I identified the sub-adult bird that I mentioned earlier.

Emmy applying silver USGS band to female nestling goshawk.

The bird is carefully passed from the bander to the Phlebotomist to extract the blood samples. A minimal amount of blood is extracted. We extract two drops for analysis of parasites via a blood smear and another 5-10 drops for later genetic analysis.

Michelle L. preparing to collect blood from nestling.

It is then time for the nestling to be returned to the nest. The total time that any bird is out of the nest is usually less than 10 minutes. In fact the whole operation usually takes less than one hour.

I'm getting ready to descend the tree.

There are many other roles within the team besides those highlighted so far. Probably the most important is the watcher which is supposed to warn the climber of an incoming attack from the adults. Some adults are more aggressive than others, but it is always a risk to take seriously. As David noted after taking a number of direct hits from an adult, "On Wednesday I was climbing with a chainsaw, this makes me much more nervous than that!" Other people are needed to record the data, take photos, hold birds, etc. It works best with 5 or 6 people, but can be successful with as few as 4.

Team for the first two climbs: Michelle, Kraig, Emmy, Rob (me), Mike. Not pictured: Thurman the photographer.
Emmy, ... your eyes are the color of a nestling goshawk...

The team dynamics shifted for the weekend. We traded Michelle J for Michelle L as Michelle and Kraig had to return to Boise. Thurman had to return to his job and was thus unavailable. However, we were joined by a new climber, David who had previously helped with camera installation and by Greg and Ayla. It all worked out great.

Ground Crew: Emmy, Michelle J, Mike.
David's view into a four nestling nest.

In a previous post I told the story of "Charlie", the nestling that we had returned to the nest during camera installation. I am happy to report that Charlie and his siblings are all still with us. However, evaluating the developmental stages of the nestlings show that Charlie is up to six to eight days behind his siblings in maturity. While it is possible that he is actually a couple of days younger, he shouldn't be six to eight days younger. Especially since males tend to mature faster than females in the nest. I therefore conclude that Charlie had spent many days on the ground without food before we returned him to the nest. I hope that he continues to be able to compete for food, especially once his siblings leave the nest.

Left to right: Charlie, his two brothers, his big sister. Note the leg size used to sex these birds.

In all, this weekend we climbed in nine nests and banded/bled 24 nestlings. But one nestling eluded us by traveling many feet out onto a branch to avoid our grasp. In honor of his/her ingenuity, Emmy named it "Lou".

Defiant "Lou".
Lou's sister, angry that she wasn't as clever. Note the purple color band.

The bravest climb of the weekend was David's last, an 80 foot Aspen. This tree not only presented challenges with its height, but also with the hot sun, breezy conditions, and getting above the three foot deep nest in the center of the tree. It was impressive to watch and I learned a great deal.

David arriving at the tallest of my 17 nests - 80 feet high.

The great news is that all birds and all crew finished the weekend safe. We have just three nests yet to climb next week before the nestling phase of the project is complete.

Guns. What do field biology and guns have in common, probably more than you would think, but not in a good way. We had two encounters with guns this past week. On the first encounter a man pulls up on his ATV to talk to me, but parks in such a way that his rifle is pointed directly at me. Whether this was an intentional act of intimidation or just clueless irresponsibility, I will never know. After I moved out of his "sights", he was friendly to me although accused most everyone else of being liars. The Fish and Game lie about how many deer are in the South Hills as he can't seem to find them on his ATV. The forest service lies about their intent to not close any roads. I am sure he thought I was lying about ground squirrel abundance as he was upset he had only been able to shoot two that day. After the requisite polite discussion, I extracted myself to get back on the more positive task at hand - finding more goshawk nests.

The second gun incident was much more serious in nature. On one of our climbs, David had just started up the tree. The adult female started her defensive maneuvers by issuing her alarm call and circling overhead. As she circled to the west a loud high caliber pistol shot echoed from about 100-150 meters away. We immediately yelled and the shooting stopped. While we cannot confirm that they were shooting at the goshawk, the timing was highly suspicious. As if we weren't putting enough stress on the bird, dodging gunfire as well? What are people thinking? Oh yea, they weren't... After completing our work, we drove by to see if we could get the license numbers, but the plate was hidden from view. Regardless, they knew they were on record. As we passed back by two hours later, their camped had been cleared out.

The team. The job we do is a difficult one, often leaving us wiped at the end of the day. However, I do my best to try to make sure that the team is learning from the work and is able to gain experience which will help them in their future career. Most of that experience is gained through the direct performance of their job - prey and habitat surveying, bird identification, banding goshawks, drawing blood, etc. However, some tasks are above their direct responsibilities. This last weekend while we were banding nestlings, I offered to educate some of the team members on our climbing technique. They would need more experience before climbing into a live goshawk nest, but a local 10 foot training tree would help them appreciate the work. Mike and Michelle J took me up on my offer.

Michelle J getting ready to tie in a hard anchor.
Instructing Mike on the use of a Jumar for managing slings.

We also try to enjoy ourselves as much as possible. Mike, Emmy, and I took David and his family back to where Karyn and I found the moose carcass. Surprisingly we were able to find it. This moose appeared to be very healthy. The teeth were in great shape. A bit of velvet remaining on the antlers indicate a late summer, early fall death. Now what would kill a young, healthy, male moose before the start of the rut. It will remain a mystery, although the cynical side of me has a pretty good idea...

Mike, Emmy, and David with moose skull and antlers.

I hope to have more great news to share after out next bout in the woods!

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