Mission: To promote the appreciation of wildlife and increase harmony between humanity and nature.

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Sunday, May 17, 2020

A Population Explosion


Since February, when I first saw the Common Ravens securing nest-building supplies in the Arboretum, I have been watching, wishing, and waiting for young. It may have been more than a century since ravens nested in this area. There is no mention of nesting ravens, or even visiting ravens, in the Arboretum bird surveys I have seen from the 20th century.  

During the last few months, I have occasionally seen ravens heading to the northwest, apparently, searching for food in the mornings and I have sometimes seen ravens at Interlaken Park. More than once, I have seen them returning to the Arboretum from the north, sometimes with food and sometimes without. It feels like I have been hearing ravens almost every time I leave my house. It has been a wonderful change.

Watching their behavior and their participation in our local web of life has been incredibly enriching. At times, it has also been a bit frustrating. For example, these first four pictures, which may be my best ever raven photos, were taken in Interlaken Park on April 29th. Even though, I have spent hours watching the ravens in the Arboretum. It feels like these photographs should have happened there instead. I can't even be sure whether this raven is one from the Arboretum pair or not.

The raven flew in from the northeast while croaking loudly and landed directly in front of me. Every creature in a quarter-mile must have immediately known its location. Since this wasn't the call I have heard the ravens use when chasing away an intruder, I have no explanation for its noisy behavior. (If you Click Here and then pick the first call from Alaska you can hear how it sounded.) 

Still, it was wonderful to see the raven, brimming with confidence. I sure would enjoy some similar disclosures while observing their nesting process. Although, it does make sense that until the young birds learn to fly the nesting process needs to be quiet and hidden. Plus, an adult raven visiting Interlaken Park probably has very little to fear. 

You might wonder if a Barred Owl could threaten a Common Raven. After all, ravens are songbirds and owls are totally meat-eating predators. Barred Owls are the largest resident, predatory, bird I have seen in Interlaken. Even though an owl's wingspan can be nearly as large as a raven's, ravens can weigh significantly more. 

In regards to encounters with Barred Owls, on the evening of April 6th, I took this photo, just to the west of Lake Washington Blvd in the Arboretum. The owl's mate was in a nearby tree. The next morning, I returned to the same area but failed to find the owls. I had just crossed the Blvd when suddenly I heard a raven, clucking loudly. I could not see it through the trees but it sounded like it was heading in my direction.

In a moment, the raven popped out of the trees with an owl briskly pumping its wings while desperately trying to stay in front of the raven. The owl crossed the street just above the traffic and made a beeline for the thick foliage of the Sequoia trees. The raven followed but appeared to be deterred by the profusion of branches. Ultimately, it must have decided that the owl was sufficiently outside of the raven's nesting territory. The raven turned and flew back towards the nest.

A raven's intimidation is not all about being a larger bird. I remember watching one of the ravens who appeared to be standing guard in a treetop about one hundred yards from the nesting tree. From what I have read this means it was most likely a male. It started clucking as soon as it saw a Red-tailed Hawk approaching. A moment later a similar sound came from the direction of their completely hidden nest. Ravens make a variety of sounds and the intruder alert sound reminds me of the noise a chicken makes, which is why I call it, 'clucking'.

The closer the hawk got the faster and more intensely the raven clucked. The raven went directly after the hawk. Red-tails can have a larger wingspan than a raven, however, their weight is fairly similar. On the upside, ravens have the potential to be a few ounces heavier.

In the photo above, the raven is on the right and the hawk is on the left. The hawk is trying to make a quick exit. A second raven (most likely the female) also started clucking and then appeared from the direction of the nest. It followed the first two birds for a short distance. Once the hawk crossed Foster Island Road the 'male' raven turned and followed its mate back towards the nest.



I have seen the same type of hawk intervention happen three different times. In this case, it was further from the nest but it did not change the raven's intensity. The hawk is the one on the bottom, rolling over in defense.


None of the three hawks wanted anything to do with an angry raven.
 
I have also seen the raven chase adult Bald Eagles out of the area, multiple times. Here you can see the eagle is straining to get lift. It was clearly trying to get up and away from the smaller raven.

Yesterday evening, while walking the dog, I heard an unusual number of raven calls coming from the Arboretum. Even though I was without my camera I could not resist the opportunity to observe ravens in action. I found three of them flying around the treetops, calling loudly. I thought one or more sounded young, but I could not see clearly enough to be sure.

Early this morning, I returned without the dog and with my camera. The ravens did not disappoint. I crossed paths with my friends, Rick and Anne, on Azalea Way. Suddenly, two ravens descended to the ground while attempting to evade the harassment of an American Crow. The ravens quickly returned to the treetops but I did see that one was carrying food.


About forty-five minutes later, I finally documented one of the adults feeding its fledgling.


A few minutes after that, I found two young - clearly wanting more food from the adult. When these birds are in flight, flashing about among branches and trees, with varying numbers of similarly black crows giving chase, it can be very hard to determine what you are seeing. Photos are helpful. 

By the way, Common Ravens and American Crows are both Corvids which explains why they look so similar. You can compare their differences in my previous post, The Mythical Raven.

In addition to the begging behavior, the photo above allows us to see some other indications of youth. For example, their red gapes. With the bird on your right, you can see just a small hint of pink at the joint where the bill hinges. With its sibling, the bill is opened wider and the pink has become more visible. Also, in the middle of the sibling's lower jaw, you can see a glow of red where the light shines through a thin membrane. I suspect when the bird is mature this area will be obscured by feathers.


The two young follow each other from tree to tree while waiting and begging the adults for food. Sometimes, they squabble just like human siblings. Earlier, I saw one pluck a downy feather off the chest of its sibling. The second bird immediately grabbed the closest piece of the feather and for a moment it looked like a tug-of-war with the offended bird wanting its feather back.

Still, on the whole, they appear to be similarly sized and genuinely enjoy each other's company. Birds of the World (BOW - citation below) lists a wide variety in the amount of time young fledglings hang around with their parents. It can be as short as a week or until winter has passed. In BOW there is even mention of an occasional third bird helping during nesting. I wonder if it might be an offspring from a previous year?

It will be very interesting to watch and see what happens with these two young ravens. It has already been over a week since I first saw one of them out of the nest. The next time you visit the Arboretum I would suggest bringing binoculars if you want to have a chance to closely observe these noisy young birds.

As I was leaving the Arboretum, I walked through the Pinetum. In the last year or two, I have seen multiple crow nests in the area. As I passed this pine tree, the crows were diving, calling, and mobbing this adult raven. The raven finally gave up and headed back toward its territory. The crows calmly returned - once the raven was east of Lake Washington Blvd. It made me realize that the raven was probably attempting to raid a crow's nest. I wonder if our growing abundance of crows in the city is the primary food source that has encouraged the ravens to return? If so, I suspect we will see an exploding population of ravens in the future. 

Actually, if our human population doubled we would call that an explosion. With the local raven population going from two to four maybe we are already in the midst of a population explosion.

Have a great day on Union Bay...where nature lives in the city!

Larry 

Recommended Citation

 Boarman, W. I. and B. Heinrich (2020). Common Raven (Corvus corax), version 1.0. In Birds of the World (S. M. Billerman, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.comrav.01

Going Native:

Without a well-funded Environmental Protection Agency, it falls to each of us to be ever more vigilant in protecting our local environments. Native plants and trees encourage the largest diversity of lifeforms because of their long intertwined history with our local environment and native creatures. I have been told that even the microbes in the soil are native to each local landscape. I hope we can inspire ourselves, our neighbors and local businesses to respect native flora and to support native wildlife at every opportunity. I have learned that our most logical approach to native trees and plants (in order of priority) should be to:

1) Learn and leave established native flora undisturbed.
2) Remove invasive species and then wait to see if native plants begin to grow without assistance. (If natives plants start on their own, then these plants or trees are likely the most appropriate flora for the habitat.)
3) Scatter seeds from nearby native plants in a similar habitat.
4) If you feel you must add a new plant then select a native plant while considering how the plant fits with the specific habitat and understanding the plant's logical place in the normal succession of native plants.

My intention in my weekly post is to include at least one photo each week and visually challenge us to know the difference between native and non-native lifeforms. 













What species is this? Is it native to Western Washington?











Scroll down for the answer.













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Horse Chestnut: This common tree is not native. Its fruit is considered poisonous and, I suspect, a native Big Leaf Maple might grow very nicely in many similar circumstances.





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The Email Challenge:

Over the years I have had many readers tell me that Google is no longer sending them email announcements regarding my posts. Even more frustrating when they go to 're-sign-up', hoping that will enable them to once again start receiving the announcements, they get a message which says 'Sorry, you are already signed up.' Google has not responded to my requests for help with this issue. 

My functional workaround is to set up my own email list and each week I manually send out a new post announcement. If you are experiencing the issue and would like to be added to my personal email list please send me an email requesting to be added. Thank you for your patience!


My email address is: LDHubbell@Comcast.Net




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This photo is a little reward for those who have read all the way to the end. 

Raven's tails do not always show their characteristic 'diamond' shape, however, their wings are always relatively longer and less rounded, as compared to a crow, plus ravens are less likely to rapidly flap their wings.

2 comments:

  1. A Comment from Rick Matsen:

    'This was such an amazing encounter. We were able to hear the fledgling calls of the hungry children. These fledgling calls can be heard on the Audubon fight. Seems like children always scream loud when they are hungry.'

    It was certainly fun to see you both and the ravens as well. The early morning is wonderfully quiet time for birding!

    ReplyDelete
  2. Thanks for your fascinating narrative on Ravens. We've had a pair in our Burien neighborhood near Seahurst Park for a few years now. I love to hear their range of sounds...croaking and clucking.

    ReplyDelete