Bob!!!! - The Case For and Against Mobbing Behavior

This is the fourth post from Karyn and my recent trip to Yellowstone National Park. A few more to come so check back!

Post 1: Eye to Eye - Sandhill Cranes
Post 2: Bullying the Bully - 3 Coyotes v. 1 Wolf
Post 3: Under the Gaze of the Phantom of the North - Great Gray Owl!

Upon our arrival in the Lamar Valley, we observed a bison carcass in the middle of the valley. This bison appeared to have died of natural causes as the carcass was largely intact. A bison carcass has the potential to be the center of the wildlife action for many days. As a result, we spent a lot of time watching and waiting for the big predators to come in. The wolves, one at a time, eventually arrived. The bears were all spotted up high and not on the valley floor. The carcass was visited regularly by a local coyote pack, Bald Eagles, Common Ravens, and Black-billed Magpies. The Bald Eagles had a nest in the valley which we could also observe - with two nestlings!

Bald Eagle, Lamar Valley, Yellowstone National Park.

Bald Eagle in nest with 2 nestlings, Lamar Valley, Yellowstone National Park.

The bison carcass provided a great opportunity for our national bird / national animal to exhibit its style by sticking its head in the butt of the bison. Since no large predators had yet found the carcass, most of the meat remained locked inside the tough hide. Only bears and wolves have the ability to "open" the carcass. Until they arrived, only the butt was available to the birds and coyotes. Aren't we impressed!

Two Bald Eagles on Bison Carcass, Lamar Valley, Yellowstone National Park.

Two Bald Eagles on Bison Carcass, Lamar Valley, Yellowstone National Park.

This brings us to the topic of mobbing behavior. Many small birds are known to mob larger birds, particularly predators. This may seem illogical, but in most cases the smaller birds are quicker to respond and can easily stay outside of the reach of the predator. Theory suggests that it is better to know where the danger is than to just know that there is danger. This is why birds fly toward alarm calls instead of away. Also, in many cases, the smaller birds can chase off the larger birds. The same theory as my previous post of three coyotes attacking a lone wolf.

While waiting in the Lamar Valley for the predators to arrive at the carcass, the local Bald Eagle took a pass by the carcass. This pass caused over 30 Common Ravens to rise from the carcass and begin mobbing the eagle. The birds swarmed around the eagle, tagging it in flight. The ravens essentially forced the eagle to the ground. Just as the eagle hit the ground, the ravens began landing as well. One landed a bit too close. In an instant, the eagle was on the raven. "Cousin Bob" was done for. The ravens screeched in horror and a few attacked the eagle grabbing his / her wing and tail. This continued until the eagle began plucking the raven. With feathers flying, apparently the remaining ravens determined that "Cousin Bob" wouldn't be returning to the clan. They gave up the fight and returned to the bison carcass.

Bald Eagle eating Common Raven, Lamar Valley, Yellowstone National Park.

After plucking the raven the eagle tried to take flight with the prize. It was not to be. An eagle weighs about 9.5 pounds, while a raven weights 2.6 pounds. This was just too much. The eagle began consuming the raven and then tried again to fly. No luck - still the same weight, just transferred into his stomach. The eagle crapped twice, but this was still not enough. He ate some more and tried again. This time he landed in a small ravine. A water-logged raven wasn't much better. He had to abandon what was left of "Cousin Bob"...

I was asked by some friends as to why the eagle would eat the raven with a full bison carcass available. There are a couple of possible reasons. First, attacking the mob seems like a great way to decrease the mobbing behavior. Second, and possibly more important, is that many raptor species require a diverse diet to survive especially as nestlings. For example, the bird I study, the Northern Goshawk, cannot survive on mammals alone or birds alone. Delivering a raven to the nest would be a great compliment to the Uinta Ground Squirrels that the eagles had been feeding their young.

Now to the question of mobbing behavior. Did the eagle decrease mobbing behavior by killing one of the mobbing birds? In my opinion it's a mixed result. The eagle clearly selected against the mobbing behavior by killing one of the mobbers. However, the "average" raven is now different as a result of this bird being taken out of the population. The "average" raven is likely faster (assuming the slowest bird was removed) and will likely keep a larger distance during mobbing (assuming the closest bird was removed). This is just a single animal, but provides great insight into the basic mechanics of evolution by natural selection. Each animal removed from a population changes the "average" for the population. If the slowest and closest are consistently removed, the population attributes can change fairly quickly.

This is one reason I find wildlife watching and field work so fascinating. It is not always about what you go there to see, but what you see while you are there.

Under the Gaze of the Phantom of the North - Great Gray Owl!

This is the third post from Karyn and my recent trip to Yellowstone National Park. Many more to come!

Post 1: Eye to Eye - Sandhill Cranes
Post 2: Bullying the Bully - 3 Coyotes v. 1 Wolf

Over the years we have made many friends with the wildlife watchers who visit the park the same time of year that we do. It is always interesting to arrive and see who else is around. Our friends Paul, Mark, and Carol all left the week before we arrived, but our good friends Jim and Joellyn were there. We had missed them last year so it was great to spend time with them. Jim and Joellyn volunteer as part of the wolf project and have a deep knowledge of the history of the wolf reintroduction in the park and the current state of the wolf packs. We spent hours with them at "Dorothy's Knoll" waiting for the wolves and bears to find the bison carcass laying in the center of the Lamar Valley (apparently died of natural causes).

We were camping just outside the northeast entrance of the park near Cooke City. Jim and Joellyn were staying in Cooke City. Each morning upon meeting up in the Lamar Valley we would compare notes on what we have seen on the drive in. This almost always included Moose and Bison, but occasionally included more exotic species. One morning Jim mentioned that they had seen a Great Gray Owl! Wow, we were 15 minutes ahead of them and had seen nothing. I pressed him for details. What does a raptor biologist do with information about the location of a rare raptor (rare for the area) during breeding season? Go look for a nest!

Great Gray Owl Global Range Map. From Wikipedia.

That evening Jim and Joellyn observed the bird again on their way back to Cooke City. Amazing. We passed slowly through the areas, but didn't see anything (except Moose). The next day Jim marked the location on a log with some Black tape. The pressure was on. I now had to find the nest. My reputation as a Raptor Biologist depended on it.

Jim's marker.

Searching for a nest sounds easy, but it is actually fairly hard. Mistletoe, a parasitic plant, grows in dense balls in trees. These look like a nest and are everywhere. Furthermore, I knew little of the type of nests that Great Gray Owls prefer. I knew they did not build their own nest as no owl builds a nest. That means it uses a Northern Goshawk nest, a Raven's nest, or some other structure. As we left the highway, Karyn suggested that we go left, but I had my sights on the right.

Karyn's vote.

We searched to the right, zigging and zagging every 50 meters out to a distance of 200 meters. We crossed the road and continued there. A carcass... a Robin... plucked by a bird... But probably not our bird. Maybe a Cooper's Hawk.

Plucked American Robin.

We decided to take a pass though the route that Karyn originally suggested. As I led out, within 5 minutes, I saw a large Mistletoe ball. Wait! There were tail feathers extending over the side! We found it! All I could see were the horizontal tail feathers. We re-positioned ourselves to get a better view.

Great Gray Owl nest in Mistletoe ball, Yellowstone National Park.

Great Gray Owl nest in Mistletoe ball, Yellowstone National Park.

Great Gray Owl nest in Mistletoe ball, Yellowstone National Park.

Great Gray Owl feather.

We kept our distance and kept quiet. Raptor nests early in the season are particularly vulnerable to disturbance. No matter how habituated a raptor may be to humans, disturbance still has an impact on reproductive success (Strasser 2010). We noted the lack of fecal material on the nest rim indicating that the eggs had not hatched or if they had, were less than 5 days old. The owl's posture indicated that they had not yet hatched. My first Great Gray Owl nest!

Since Jim had gone to such work to mark the location, I wanted to take him to see the nest. This provided a great opportunity to share my knowledge of owls with him.

Raptor Rob (left), Jim (right), Great Gray Owl nest in the distance.

Scoping the nest!

I asked Jim to take another look in three weeks to let me know how many nestlings hatch.

Bullying the Bully - 3 Coyotes v. 1 Wolf

Here is the second of many posts on Karyn and my recent trip to Yellowstone National Park. Wolves are one of the primary reasons that we travel to Yellowstone each year on vacation. While we have observed wolves in Idaho, the population has been lowered to a point that regular observation is no longer feasible. Actually, the population in Yellowstone is also at its lowest level since 1999. The decline in both locations is due to human hunting, inter-pack conflicts, and changing prey dynamics. Even though hunting is not allowed in Yellowstone, many of the packs leave the park in winter and the hunting pressure just outside the park has been high (12% of Yellowstone's wolf population were killed by hunters outside of the park in 2012). Regardless, there is still a much better chance of observing wolves in Yellowstone than in Idaho.

Luck was not on our side during the first couple of days in the park. For the first time in our decade of visits, we failed to observe wolves two days in a row. All of that would change on the third day.

Two black wolves from the Junction Butte pack would entertain us on the south side of the Lamar River near Jasper Bench. They appeared to have bones from an unidentified carcass. We watched as they were harasses by coyotes and eventually climbed the hill and headed toward their home range (different coyotes than referenced below).

On the north side of the river below "Dorothy's Knoll" was an uneaten bison carcass. The carcass did not appear to have been killed by predators and laid largely intact for many days. Wolves were scarce and the grizzly's were at high elevations (we observed many up on or near the snow). The two junction butte wolves must have been just out of smell range of the carcass. After the two wolves crossed over the ridge, we expected the action was over. Wrong! Karyn looked behind us and spotted a black wolf heading our way. It would pass within 50 meters on its way to the valley floor. She was headed for the carcass!

Black wolf (possibly of Lamar Canyon Pack) - Lamar Valley, Yellowstone National Park.

Black wolf (possibly of Lamar Canyon Pack) - Lamar Valley, Yellowstone National Park.

Her path to the carcass took her right by a coyote den. Wolves are notorious for bullying coyotes. They will dig up a den and kill the puppies if they get the chance. We have personally observed this on two separate occasions, and heard of a number of similar encounters. It is estimated that the coyote population dropped in half after the introduction of wolves into the park.

Today was not the day for the wolf. With three coyotes present against one wolf, the odds were clearly stacked against her. The coyotes are quicker and had teamwork on their side. They would surround the wolf, each biting when the wolf was facing the other way. They would speed by at full speed, biting as they passed. The following sequence shows the engagement as the coyotes escorted the wolf away from their den. It wasn't about the carcass as the harassment stopped once the wolf arrived for a meal. As soon as she stepped away, the onslaught continued. This process would repeat during the week anytime a lone wolf would visit the bison carcass.

Black wolf and three coyotes - Lamar Valley, Yellowstone National Park.

Black wolf and three coyotes - Lamar Valley, Yellowstone National Park.

Black wolf and three coyotes - Lamar Valley, Yellowstone National Park.

Black wolf and three coyotes - Lamar Valley, Yellowstone National Park.

Black wolf and three coyotes - Lamar Valley, Yellowstone National Park.

Black wolf and three coyotes - Lamar Valley, Yellowstone National Park.

Black wolf and three coyotes - Lamar Valley, Yellowstone National Park.

Black wolf and three coyotes - Lamar Valley, Yellowstone National Park.

Black wolf and three coyotes - Lamar Valley, Yellowstone National Park.

Black wolf and three coyotes - Lamar Valley, Yellowstone National Park.

Black wolf and three coyotes - Lamar Valley, Yellowstone National Park.

Black wolf and three coyotes - Lamar Valley, Yellowstone National Park.

Even the bison join in the pandamonium...

Black wolf, bison and three coyotes - Lamar Valley, Yellowstone National Park.

Eye to Eye - Sandhill Cranes

Karyn and I just returned from nine days in Yellowstone National Park. This is the first in a number of posts on what we saw and experienced.

On our first full day in the park, we found some very friendly Sandhill Cranes. I had never been within a 100 meters of a sandhill before, but these walked right up to the road. These birds are majestic and goofy at the same time. I like everything about them. Their call is amazing. It makes me pause every time I hear it, especially from about 10 feet away! Enjoy!

Sandhill Crane - Blacktail Lakes, Yellowstone National Park.

Sandhill Crane - Blacktail Lakes, Yellowstone National Park.

Sandhill Crane - Blacktail Lakes, Yellowstone National Park.

Sandhill Crane - Blacktail Lakes, Yellowstone National Park.

Sandhill Crane - Blacktail Lakes, Yellowstone National Park.

Sandhill Crane - Blacktail Lakes, Yellowstone National Park.

Sandhill Crane - Blacktail Lakes, Yellowstone National Park.

Sandhill Crane - Blacktail Lakes, Yellowstone National Park.

Sandhill Crane - Blacktail Lakes, Yellowstone National Park.

Nine Beautiful Sunrises - The Hunt For The White-headed Woodpecker

My first assignment of the summer has drawn to a close. Interspersed with working on research manuscripts and teaching classes, I have spent nine days during the past three weeks surveying for woodpeckers. This is the first of seven different projects I have going on between now and this fall. I will be a busy man.

Pre-sunrise - Rattlesnake Ridge.

Actually Working!

This particular project involved surveying for White-headed Woodpeckers and Pileated Woodpeckers in the Emmett Ranger District of the Boise National Forest. These two species are Management Indicator Species for the forest. The idea of a Management Indicator Species is to allow the forest service to monitor fewer species, but to choose species which represent the overall health of the forest. The forest has a long-term monitoring plan in place to survey these same routes each year. We would find many Pileated Woodpeckers, but no White-headed Woodpeckers during the surveys. I did have one White-headed Woodpecker in my camp the night before a survey, so that one may count.

Pileated Woodpecker - Digiscoped through my binoculars!

The monitoring plan specifies 10 survey transects in each of the five ranger districts. The Idaho Bird Observatory (my employer) only has the contract for one of the districts, thus we had ten total surveys, of which I performed nine. Each transect is set up along a seldom used forest road or trail. It consists of ten separate survey points each separated by at least 300 meters. The survey begins 30 minutes before sunrise at the first point and must finish by 10am. At each point the surveyor logs every bird they see or hear, the direction, and the distance, for a period of ten minutes. Then its on to the next point. Some surveys require a 20-30 minute hike to get to the first point, so it can definitely be an early morning.

Datasheet from a particularly crazy point - lots of birds in close - no woodpeckers.

The job presents some unique challenges. For the most part the hiking is easy as most of it is along roads or trails, although one in particular had a very large number of downed trees to navigate. Snow fields were occasionally an issue as well, but fairly manageable. The 15 degree morning was a bit of a shocker, but once I got going all was good.

Survey Point #5 - Rattlesnake Ridge.

One of my favorite morning past-times is to scan for peering eyes while I eat my breakfast. My headlamp illuminates the animal's eyes but not their body. I had three sets staring at my one morning and one set on another morning. I assume that they were all deer, but I don't know for sure. People always ask if I am afraid of animals in the area, usually wolves. Generally I am not afraid of anything except mountain lions. I enjoy watching for sign.

Black bear print in mud with ice.

The biggest challenge is to identify every bird by sight or sound. I am very comfortable and confident on the ten woodpecker species which are the priority, but not across the entire avian world. There are over 300 possible species in Idaho. I must occasionally use that feared code UNBI - Unidentified Bird.

Ticks. I hate Ticks. Enough Said...

Of the nine surveys I performed, my favorite was Rattlesnake Ridge, north of Crouch, Idaho. This was the most difficult, had the most downed trees to climb over, the most snow, and the second largest number of ticks. The birds and the views made it outstanding. I would see seven of the ten woodpecker species in Idaho during this one survey (Pileated, Downy, Hairy, Black-backed, Red-naped Sapsucker, Williamson's Sapsucker, and Northern Flicker). Unfortunately, that list did not include the White-headed Woodpecker. At one survey point a Black-backed Woodpecker flew to a tree about 10 meters away and started drumming. A Hairy Woodpecker and a Red-naped Sapsucker flew over in protest, perching on trees about ten meters away as well. All three were drumming away and I was standing in the middle. A Williamson's Sapsucker joined in about 50 meters away It was woodpecker mayhem! Apparently the Black-backed is the enemy as they all seemed to tolerate each other up until that point. Maybe it was just one too many birds for the area. This area is an old burn and many of these species like burns. At the top of the ridge I observed a Merlin diving on a group of Mountain Bluebirds (unsuccessfully). I saw my first Gray-crowned Rosy-Finch on the mountain. There were Western Bluebirds, Townsend's Solitaires, Cassin's Finches, a Cooper's Hawk, and all of the other usual suspects. And the views... Being above 7000 feet at the first of May is remarkable.

View from Rattlesnake Ridge.

As with my other fieldwork, this project was an awesome experience. It took my places I would not have otherwise gone, I saw things I would not otherwise have seen, and it taught me things I would not otherwise have learned. I can't wait for the next project.

What's next on the agenda? Some vacation in Yellowstone, some database work another project (American Kestrels), beginning a manuscript on sagebrush songbirds, and then returning to the Sawtooth National Forest to pursue the Northern Goshawk in June. I follow that with another woodpecker project, some Black Swift surveys, and then will travel to Spain to collaborate on migration research with Fundacion Migres out of Tarifa. Then its back to trapping migrating raptors this fall. It will be a fun filled summer for sure!

Sunrise - Nero Creek.

After the survey at Second Fork Squaw Creek.

The disgraceful, but usual response of Idahoans to travel restrictions.

Spotted Towhee

Spotted Towhee.