A Favorite Pin Oak Tree: 19th Century Origins

The Pin Oak tree at the edge of the road in Eliza Howell Park is one of my favorite trees. It stands alone, with enough room for its branches to spread. 

At this time of the year, the leaves are fallen and the branches are bare.

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I first started paying close attention to this oak because the birds are attracted to it. Warbling Vireos have nested here twice in recent springs and both Red-bellied Woodpeckers and Blue Jays are all over it in late September and early October, collecting acorns.

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Photo by Margaret Weber

This is a quite large – and old – Pin Oak, a species that does not live as long as some other oaks. After having been asked several times how old it is, I decided to try to find the answer. There is no exact method of knowing the age of a living tree, but there is a widely used method of estimating the age.

The steps in estimating tree age are these:

  1. Measure the circumference of the tree at 4 ½ feet from the ground.
  2. Divide the circumference by pi (3.14) to get the diameter.
  3. Multiply the diameter (in inches) by the “growth factor” that has been identified for the specific species, based on how fast growing it is. (Different organizations have published the growth factors for different species.)
  4. The resulting number is the approximate age of the tree, in years.

Pin Oaks are moderately fast growing and have been given a growth factor of 3.0.

It is difficult to measure the circumference of a large tree by oneself so recently, when accompanied by Charon, another Eliza Howell enthusiast, we undertook the measurement.

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At 4 ½ feet high, the tree measured exactly 12 feet in diameter (144 inches).

144 divided by 3.14 = 45.86.

45.86 times 3.0 = 137.58

Using this method to estimate age, the tree is about 137 or 138 years old.

137 years ago was 1883. This is just an estimate, but it is probably safe to say that this tree began to grow before the twentieth century, long before this property was donated to Detroit for parkland.

It was already over 100 years old when I started enjoying it, appreciating it in all seasons. On hot summer days, when someone else has not claimed the spot, I park the car in its welcome shade as I take my walk.

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Across the road is the prairie flower field and the Pin Oak sometimes makes a lovely background for a flower picture — Joe Pye Weed in this case.

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Pin Oak leaves turn late in the Fall, in November in Eliza Howell. The bronze (?) shade is not as striking as the leaves on some other trees, but there is something very attractive about it.

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As oak trees go, Pin Oak trees do not have a long lifespan. This one is perhaps older than average. I hope it continues to provide beauty, food, shade, and nesting habitat long after my nature walk days are over.

Blue Jays Harvesting Acorns: Coming Soon

It is almost September and the acorns are nearing maturity. A fascinating Eliza Howell bird-watching occasion will begin soon.

Blue Jays in southern Michigan in September are both migrants and year-round residents. Blue Jay migration is different from that of most other birds. They are found throughout their general range in both summer and winter, but large numbers move from one location to another in spring and fall. Mid-September to early October is the time of the largest numbers in the park, many more than in the rest of the year.

Eliza Howell has a number of large oak trees within the road loop and the acorn crop is the main attraction for the jays.

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Photo by Margaret Weber

Last year (2017), I did more careful observation than previously. It began with noticing that many of the acorns that I was crunching as I walked under one of the pin oak trees were really just the caps; there were far fewer nuts on the ground. I thought that the jays were probably responsible for removing the caps but I had never really given careful attention to their harvesting behavior, beyond observing their preference for oak and beech trees.

I decided to watch. In the late morning of September 22, I sat in the shade of another oak tree and watched the pin oak the Blue Jays were frequenting.

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My observations:

  • The number of jays coming and going was considerably greater than I had expected. Those flying out almost always often had an acorn in the beak.
  • Individuals in the tree moved quickly from one small branch to another, efficiently securing acorns (with only a few being dropped or knocked to the ground).
  • After picking an acorn, the jays flitted to a larger limb, where they held the acorn with the feet and pecked or hammered at it.
  • While in some cases they might have been breaking the acorn open and eating it, the hammering was most often to remove the cap, which fell to the ground.
  • The jays then appeared to swallow the nut whole and move on to get another.
  • I knew that jays do not eat acorns whole, so I wondered exactly what was going on. More watching revealed a bulging throat pouch in some of the jays.

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Photo by Margaret Weber

I knew, of course, that Blue Jays carried off acorns to store for future use, but I assumed they carried only one at a time, in the beak. Reviewing some published reports on the acorn storing behavior of jays, I found that they typically carry several acorns at a time to cache. They hold acorns in their “gular pouch” (usually 2 – 3, sometimes more), may carry another in the mouth, and have in the beak as well. They take them to the caching location (which may be a half mile away or more), regurgitate them, and hide each individually on the ground.

The next day I went back for further observation of the jays in the same pin oak tree. From a stationary position where I could see the entire tree from top to bottom, but where I could not observe the “back side,” I watched the Blue Jays coming and going to the tree for a 30 minute period on a sunny morning, from 9:56 a.m. to 10: 26 a.m.

  • I recorded jays flying into the tree 94 times and flying out 98 times.
  • I estimate that there were 7 or more birds in the tree at any given time.
  • I have no way of knowing how many individual jays returned how many times, so cannot estimate of the total number of individuals harvesting pin oak acorns from that one tree.
  • If I assume that the average trip out included at least 2 – 3 acorns, and recognize that this was just a 30-minute segment of one day (the jays have been “working” the tree for a number of days and for hours each day), it is likely that the number of acorns harvested by Blue Jays from this one tree this one year may be 8,000 or more.

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Photo by Margaret Weber

I now have additional questions. Based on what I observed, I now wonder whether I can continue to assume that most of the Blue Jays present in the park every September are migrating through. As I watch the jays in the tree, there was clearly much more “pouching” of the acorns than eating on the spot. Do migrating Blue Jays that are not going to be in the area for more than a short period of time harvest acorns and cache them? Maybe a number of year-round jays from neighborhoods outside the park come to the park in September for the acorn harvest?

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The acorns in August remind me of what is coming and I am looking forward to September watching. Perhaps I will learn a little more about these common birds this year. Perhaps I will have additional questions.