Last Sunday brought the official kick off of my second field season studying Northern Goshawk (Accipiter gentilis) breeding ecology within the Minidoka Ranger District of the Sawtooth National Forest. This study is the core of my thesis work in the Raptor Biology Program of Boise State University. The first few days could not have been more different than last year! Last year we arrived to 2 feet of snow on the ground with more coming down. This year it was near 80 degrees Fahrenheit and very dry and dusty. As you might imagine, progress came much more quickly this year!
The 2012 Team Goshawk: Lauren (a.k.a. the Traitor), my field assistant from last year, moved on to a new endeavor more in line with her future studies. As a result, I have hired two new undergraduate students for the 2012 team - Emmy and Mike. They had a great week learning about goshawks, driving ATVs, navigation in the forest, GPS use, and my specific survey protocols. They have already proven their enthusiasm and abilities to be great assets to the team!
|Emmy performing a trial prey survey in mixed terrain.|
|Mike performing trial prey survey in open habitat.|
Searching for Nests: We use a number of different techniques for discovering occupied goshawk nests. Prior to the first of June, we use passive methods of simply searching through the forests. During last years field season we discovered more than 60 nest structures that could possibly be used by goshawks. During our first week, we visited 57 of these structures to check for goshawk presence. Six of these were occupied by goshawks and two were occupied by Red-tailed Hawks. While searching these, we found a seventh occupied goshawk nest which was previously undiscovered. Wow, by the third week last year I only had two confirmed goshawk nests and could only access about a third of my study area! In fact, we discovered the first three nests this year within three hours of returning to the field! The first three nests we checked were all occupied!
If you followed my progress last year, you might remember the story of Chuck. Chuck was the first nestling I observed, was the first nest tree that I climbed, and the first nest camera that I installed. I was saddened to view Chuck's old nest tree. It has been pushed over by other broken trees to the point it is no longer usable. Hopefully we will discover the adults nesting again somewhere nearby.
Last year we found that one nest tree had been cut down by firewood collectors. Luckily, it was not occupied at the time, but it had shown that it had been visited by a potential user (fresh greenery had been added to the nest). After discussion with the wildlife biologist of the forest, we decided to mark these important resources to help prevent future destruction. Thus, we have so far installed 24 signs to help raise awareness of the importance of the nest trees. We skipped the trees which are currently occupied (to minimize disturbance) and those that are so far degraded to not be of much future value.
After the first of June we will return to the territories where an occupied nest has not been confirmed and try to detect goshawks using a call broadcast. This consists of a three minute protocol at each point where we play a recording of a goshawk alarm call, then listen/watch for a response. This will be performed at points 300 meters apart throughout all appropriate habitat out to a distance of 1700 meters for the historical nesting location. This can consist of up to 35 call points per territory. That will take up a big chunk of our time over the coming weeks.
If that isn't enough, I have also predicted high quality habitat for nesting using Geographic Information System Analysis. This resulted in another 250 locations to perform call broadcasts which are outside of any known historical nesting territory. Last year this yielded one additional confirmed territory and one possible territory (had a response, but no nest was found). That's over 500 call points to complete!
Nest Cameras: I will once again be installing nest cameras in three nests to help identify and quantify prey deliveries to the nest. As the top diet choice of goshawks in many parts of the world, tree squirrels, are naturally absent from the South Hills, quantifying the goshawk diet in this unique landscape will be one of the main chapters of my thesis. I expect the first installation will occur during the next two weeks.
Prey Surveys: The second chapter of my thesis relates prey abundance with nest occupancy and success. To evaluate the prey abundance, we will perform six 750m prey surveys randomly placed within each territory. These surveys are walked point to point while recording each potential prey item observed (birds and mammals). The distance to the prey item is recorded using a laser rangefinder. These values are then integrated into a Distance Sampling analysis to produce prey abundance estimates for each territory. With 150 prey transects to perform, we will be in excellent hiking shape by the end of the season! That's a minimum of 140 miles of hiking for just the prey transects, all off-trail through whatever the landscape presents!
One of the great things about field work is discovering the things you don't expect to see. While searching for nests this last week, I found a large nest which could belong to a Bald Eagle. This was a surprise and not located in what I would consider ideal habitat for Bald Eagles. While still investigating the possibilities, what I do know is that a large group of adult Bald Eagle feathers were scattered across a 15m radius around a nest tree. These are assumed to be molted feathers as they were fresh, none were damaged, and they were clean on the shafts (no flesh remaining). There was also about 10 times more fecal splatter around the base of the tree than I have observed around any goshawk tree. There was no sign of birds in the area. It's a fun side project to investigate.
Next week we will once again hit the field to complete our first official prey surveys, continue monitoring occupied nests, begin camera installation preparation, and start with call broadcasts. By the end of the week, we could have our first camera installed. I expect another fruitful week!