Wednesday, June 20, 2012

Intimate Encounters with the Northern Goshawk

Welcome to the third update for this year's field season studying the Northern Goshawk for my Master's thesis in Raptor Biology. My field assistants and I have just returned from nine days in the field with a new collection of adventures! The season continues to be a huge success. It is hard to believe the season is over half way completed with only three weeks left in the field!

Adult female Northern Goshawk. South Hills Idaho, 2012.

We have now discovered and are monitoring 14 occupied goshawk nests! This is four more than I had last year. During my last post I indicated a possible issue with the late season snow storm. During that snow, we were only able to confirm that four of the ten nests were still occupied.

Goshawk nest buried in snow. (Photo: Emmy Tyrrell).

The good news is that all of the nests were still occupied after the storm. So far, we have observed that 13 of the 14 nests have successfully hatched young. The only nest where we have yet to confirm hatching is occupied by a sub-adult female. Sub-adult females are known to breed later and have much lower hatching success than full adults, but we are still hoping for success. We continue to survey for additional nests and I won't be surprised if we find one or two more.

Raptor Rob (me) broadcasting goshawk alarm call to solicit a response. (Photo: Karyn deKramer)

Nest Cameras. During this bout in the field we installed three nest cameras to help me identify and quantify the breeding season diet of the nestlings. This information is the foundation of the first chapter of my thesis on goshawk diet and provides critical support for the second chapter which deals with the influence of prey abundance on nest occupancy and success. The installation of nest cameras require a significant disturbance to the birds, something that we do not take lightly. Every measure is taken to limit our time at the nest and get out as soon as possible. We also wait until the nestlings are 8-10 days old to limit the chance of nest abandonment. Of the three other studies which have deployed a similar procedure, none have resulted in nest abandonment. This year I had a very eager volunteer to climb the trees and install the cameras - Dr. David Anderson. While I am capable and willing to climb myself (completed 9 climbs last year), I was very willing to share the excitement of climbing the trees and to learn from someone with the depth of experience that David brings. David has many years of experience climbing large trees in the tropics as the focus of both his master degree and Ph.D. degree. It was a great opportunity to see him in action. I should note that these were the first climbs that David has performed into goshawk nests.

Upon reviewing my gear David was reluctant to use the Lacrosse helmet which I specifically acquired after last year's in-nest attacks. His impression was that the extra bulk and reduced visibility were not warranted. However, the morning of his first climb he was broadcasting a goshawk alarm call to solicit a response. A response is exactly what he got! The adult goshawk swooped toward his head, circled around and hit him from behind! His hat went flying through the woods as his ears rang from the impact. As I have personally experienced this on numerous occasions, it has a way of building a deep respect for these birds and their striking force! Anyway, David decided the helmet was a pretty good idea.

David's self-portrait in the tree.
One of my encounters with an angry goshawk!

The first camera install was in a tree with a female that has to date not been very bold in defense. While she protested loudly and circled the tree, she never actually made contact with David during the climb. The team performed well, everyone fulfilling their critical roles. David climbed, I provided climbing support, Mike managed the video equipment on the ground, and Emmy took pictures and provided the most important function of all - to warn the climber when the goshawk is coming in for an attack. You don't want to be in a dynamic move when you take a direct hit from a bird!

David climbing first tree. (Photo: Emmy Tyrrell)
Me providing climbing support. Hard to look up in noon sun! (Photo Emmy Tyrrell)
David on rappel. (Photo: Emmy Tyrrell)

David didn't take photos in the first nest, but this is what he found in the second!

Three nestlings. Front left is definitely female! Look at the size of those legs! (Photo: David Anderson)

We were in and out of the territory just under the allotted time goal that we had set. We then moved on to the next nest for the second camera install. The female waited patiently on the nest as we set up for the climb. Once David moved part-way up the tree, she started her attack. Unlike the first female, this one was playing for keeps. David took many direct hits during the climb. On his back, on the helmet, wow! When he was just 3 feet under the nest, the female returned to the nest. She looked prepared to defend the nest via hand to talon combat! I had never seen this before. I warned David that this was unusual and he would have to make the call to abort if necessary. It didn't come to that as she left the nest, although she continued her aerial assault. The second camera was successfully installed!

The Rescue. David returned to earth and started to un-clip from the rope. Just then he spotted a nestling on the ground. Was it one of the three or was it a fourth nestling? Did we cause this or was it there before? It was amazing that we had not stepped on it. This produced an ethical dilemma and we had little time to consider. Should we put it back? If we had caused it, then definitely. If we had not, then returning the bird to the nest could negatively affect the surviving nestlings. Returning the bird could affect the lifetime reproductive success of the remaining birds. Hmm. None of us were going to just leave it to die. In true rockstar fashion, David once again went up the tree to return the bird. This nestling would hereafter be referred to as "Charlie" (not to be confused with "Chuck" from last year).

David depositing "Charlie" back into the nest! (Photo: Emmy Tyrrell)

We were reasonably sure, although not entirely, that we had not caused the nestling's departure from the nest as next to it on the ground was a nearly whole, decapitated Northern Flicker. Either the flicker also fell, or the parents were trying to feed the bird on the ground. Regardless, what is a 12 day old nestling going to do with a whole flicker? Anyway, we proceeded with the rescue plan. Here is the nest camera footage of "Charlie" being returned to the nest (in double time).

I am happy to report that as of four days later all four nestlings were still alive and doing fine. The third and final install went off without a hitch. Thanks again to David for putting in the tough work.

Nestlings in third camera nest. (Photo: David Anderson)

Changing Dynamics. As the season progresses, the dynamics of goshawk detections change. First, with time, the adults become more responsive to our call broadcasts. However, they also spend more and more time away from the nest increasing the chance that we will miss them at a nest or detect them somewhere else. Now that the females are spending more time away from the nest, we also generally experience many more sightings as both the males and the female are out hunting.

One of our observations was that a nesting female had a color band on her leg. This color band is consistent with the type I apply to the nestlings. Before my study, color bands were last applied to nestling goshawks in the South Hills in 2004. It was important to understand dispersal behavior to identify this bird. As a result, we spent five hours in the nest stand with a spotting scope to be able to read the numbers on her band. We were positioned far enough away so as not to disturb the bird, but close enough that a 60x scope could be used to read the band. After five hours I finally got the code. The band number reveals that this female was indeed banded in the South Hills in 2004 as a nestling. Usually females will disperse a greater distance than this (average 50km), but the island type nature of this forest forces them to stay close to home (within 20km) or move much further than the average dispersal distance (80-200km). This bird stayed home.

While watching this female and trying to read her band number, I witnessed some great interactions. First, her nestling started to stir. The adult female then left the nest in a flash and chased off the adult male which was perched nearby, as if to tell him to go get dinner. She called off and on for a few minutes. 26 minutes later the male returned with a Ruffed Grouse chick! Dinner on demand! Before I was done I would see another similar incident.

I took my good camera to get some better goshawk photos. Here are some of my results.

Female Northern Goshawk.
Female Northern Goshawk in nest in dead Aspen.
Karyn's shot of a female on a nest in live Aspen. (Photo: Karyn deKramer).
Duck! Me being bombed by a male goshawk. Shot from the hip!
Each nest is unique. This one appears new this year.
Northern Goshawk.
And another.

The Moose. The South Hills are a great place for moose. Each of us have had a number of encounters with these beasts so far. A nice bull welcomed us back to our cabin.

David posing with bull moose.

I even had one on a prey survey! Do you think a goshawk could take a moose? This guy paralleled my path and then turned toward me. I was at least 500 meters from the nearest tree. Wow, for a while there I felt somewhat vulnerable. I tried to look big and he eventually waved off.

Moose on prey survey.

Karyn even got her moose. While riding down to the southern portion of my study area, I was just telling her that this was an area that I had seen moose tracks. Just that instant she calls out "Moose!" There she was with the youngest calf I have ever seen.

Moose and calf south of Monument Peak.
Quite a show!

Of course, all living things must eventually meet their demise. On another prey survey, Karyn and I happened upon this complete carcass.

Dead bull.

Then there are the other animals that we happen across: deer, elk, jack-rabbits, cottontails, coyotes, marmots, etc. When you walk randomly through the woods, who knows what you might find.

Mule deer calf I almost stepped on.
Horned Lizard.
Hundreds of types of butterflies!

Thank you for reading. My next report will be out in approximately two weeks.

1 comment:

Dianne C., Humano-gaian said...

Fantastic pics, and great adventure. thx for sharing!

One benefit of returning Charlie is that the parents would not have to divide their time between the nest and the ground. But yes, all kinds of factors to consider.

Dianne C.