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American Kestrel Nest Box Project: Year 5 Surprises and Milestones

August 4, 2020 Category: ,
Banding the first chick of the season!

What an exciting year for the American Kestrel Nest Box Project! This marks the 5th year that boxes have been monitored and chicks have been banded in the Sax-Zim Bog. Because this is the 5th year of monitoring, we are one step closer to reporting on the data that has been collected from the boxes over the course of the project. This year, as with all of our other years of monitoring has not lacked surprises or learning opportunities. Here is a run-down of Year 5 of the American Kestrel Nest Box Project!

A top-down view into a kestrel box.

Each monitoring season begins with the usual cleaning of nest boxes. It is important to maintain boxes, as chicks are very messy inside the boxes and other creatures use them during the winter months (especially mice and voles). We decided to clean out boxes in the second week of April, as we did last year. Not to our surprise, kestrels were already in the area and checking out potential nest sites at no fewer than 5 boxes! Notes were made on the condition of a few boxes, minor repairs were made, and we even removed one box due to the extremely unsafe lean to one of the power poles that had a box attached. In the next few weeks we will be reviewing notes, making further repairs, and even adding an additional 15 boxes to hit our target of 50 boxes in the Sax-Zim Bog!

The first eggs of the season were documented on May 1st, but there were a couple of nests with nearly full clutches of 5 eggs at this time, meaning that eggs had begun to be laid in late April! For the Sax-Zim Bog, this seems pretty typical of our kestrels: Arrive in late March and early April, lay eggs by late April or early May. This year, however, there were some exceptions and surprises…

One of two chicks banded from Box 38! We likely missed banding 2-3 siblings, as the 2 we did band were nearly ready to leave the box.

All in all, of our 36 usable boxes, 17 were occupied (a record) and 15 boxes successfully fledged chicks (also a record)! We had one nest abandoned after the lid of the box blew off and one nest failed. A total of 61 chicks were banded this season (another record!) and we now have banded 192 chicks as part of this project. The first boxes of kestrels were banded on June 19th, which is a fairly average date for the first nest boxes to be ready to band. Typically, we will need 3-4 banding sessions to band all of the chicks in a season, with most of the nests getting banded during the “second round” of banding during late June. This year, however, turned that upside down. We ended up banding a box at our latest date ever (July 29th; more on this box later). Not only that, but we banded most of our boxes during our “third round” (7 boxes) AND we “found” a new box during this session! We had 3 boxes with tree swallows this year, and a first for us: A red squirrel raised a litter in one of our boxes!

Lost 38

A look at Box 38, inconspicuous as ever.

I referenced above that we “found” a new box during our third banding session. It just so happens that we found “Lost 38” en route to banding another box. As we were driving along Western Avenue out of Meadowlands, I noticed a box…. with a kestrel head sticking out of it! This box was not on our route and not one that had been monitored at all for the last 5 years. We finished banding the box we were traveling to and doubled back to have a look inside this new box. To our surprise, there were two very old (28 days old!) kestrel chicks in the box, quite literally hours/minutes away from leaving the box! We documented the orientation, height, and GPS coordinates to this box and added it to our existing list of boxes! Very likely, this was a box placed during 2018 when we placed a number of new boxes up in the Bog, but due to a clerical error missed documenting its location. What a nice surprise and welcomed addition to the project.

The mysterious Box 35

Perhaps the biggest surprise of this season regards Box 35. At first glance, this was going to be fairly typical box: Adults arrived near the site April 11th and volunteer Kestrel Monitor Jean reported the female was sitting in the box May 8th (presumably on the first eggs she had laid). However, after that date, things got a little weird. There were no eggs or kestrels during the next visit, May 20th. On Jean’s third visit, May 30th, kestrels were present and there were 3 eggs in the box! Ok, back on track… except… on the next visit, June 8th, there were still three eggs and no kestrels present. This is odd because in our experience so far, there should either be more eggs laid at this point or the first egg of the clutch should be close to hatching. No matter, Jean kept monitoring. On the next visit, it was hopeful there would be either more eggs, chicks, or total abandonment of the box (which happens for a number of reasons in the bird world). What Jean found was none of the above: 7 EGGS WERE PRESENT! And those 7 eggs remained present and the female kept incubating these eggs up until the 7th of July.

Now, this is where things really get interesting. I told Frank about this oddity. Usually, American Kestrels lay 3-5 eggs in a given location during nesting season. He had never heard of more than 5 and so asked around to folks he knew monitoring kestrels across the US. He found out that one nest this year in the Twin Cities area had 6 eggs laid, which hadn’t been observed before at the site, and again is a bit of an anomaly like our 7 eggs. Keeping this in mind, we were to keen to see what would transpire: would all 7 eggs hatch? Did the initial 3 eggs fail and the female laid more eggs? The weeks moved ahead and on July 29th we planned on banding the chicks in this box.

We arrived at the box, climbed our ladder, and opened the box to find… 4 chicks! Great news; Perhaps the first three eggs failed and the new four were successful. But, there is something more interesting than just 4 chicks. The chicks ranged in age from 21 days at the oldest to 15 days at the youngest! To date, this is the greatest range in ages from any box we have banded over the last 5 years.

The oldest chick from Box 35, a male aged about 21 days.
This is the oldest female chick aged about 18-19 days old.
The next oldest female chick, though younger than her sister at about 17 days old.
And the youngest female from Box 35 aged about 15-16 days old, and very difficult to sex.

Usually, hatching and development is fairly close (1-2 days apart), but we had seen nothing like this before! So, being as well connected as Frank is, he called a friend who has been monitoring American Kestrels in Massachusetts to see if this age range was normal and to try and get more information about the 7 eggs laid. From this conversation we learned a few things: 1) Kestrels can be staggered as distant as our chicks in normal nesting conditions. 2) 7 eggs is incredibly anomalous and in 30+ years Frank’s friend said she had never seen any more than 5 eggs in a box. 3) Kestrels could potentially double-clutch (lay a second batch of eggs after success or failure) if there was an early failure and in this case all 7 eggs could be from the same female. All of this was great information, but our mystery still remains. Perhaps the initial female (or male) was killed after laying the first three eggs and the nest was restarted after the new pair was formed. Perhaps the initial clutch of three failed and the four new eggs hatched and were successful. Perhaps the female actually did lay 7 total eggs and every other egg failed resulting in 4 chicks of very different ages. I think most likely is scenario one: one of the adults was killed and the other adult found a new mate, but used the same box. We will probably never know, but will certainly relish this mystery for years to come!

Three unhatched eggs from Box 35. It is not uncommon to find an unhatched egg or two during the monitoring season.

Moving Ahead to Year 6

What is next for the American Kestrel Nest Box Project in the Sax-Zim Bog? Well, as mentioned above, we are going to be placing the final round of boxes throughout the Bog and repairing/replacing existing boxes this August. Our initial data will begin to be organized and I will hopefully be giving a talk about our project at the Minnesota Ornithologists Union’s annual Paper Sessions in December, but this may or may not happen due to the pandemic. This project just so happens to be contributing data to a few other projects, some of which are in their final stages and hopefully we can share some of those results in the coming months. There is a lot to look forward to in 2021!

As always, this project wouldn’t be possible without Frank and Kate Nicoletti who placed the initial boxes in the Sax-Zim Bog. And monitoring wouldn’t be possible without our intrepid box monitors Mary Gabrys, Jean Elton-Turbes, Sarah Beaster and her daughters who put in lots of time checking boxes, submitting data, and sharing their discoveries! For the first time since the project started Kristina and I also monitored boxes, as we were down one volunteer this season, and I would like to thank her for her help this season, as well. I also would like to give a thank you to David Alexander who came out with Frank and I to help band chicks on our busiest day! And last, thanks to everyone who built boxes for our use in this project!

Two very old nestlings (26-28 days old) showing the differences in plumage between male and female American Kestrels.

What an amazing year for American Kestrels in the Sax-Zim Bog, and I personally cannot wait to see what next year holds! If you are curious to read more about our project, check out these old blog posts here, here, and here.

— Head Naturalist Clinton

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