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Posts categorized Mike Coll.

Summerhill Preserve Kestrels 2015

American Kestrels in the nest box

American Kestrels in nest box
(photo – Ron Zigler)

By Mike Coll Preserve Manager

For the second straight year, the nest box at our Summerhill Preserve successfully fledged American Kestrels. This year there were four young.

This video shows one of the adult birds flying up to the box to feed the young (in slow motion):

Here you can see the young birds inside the box. They fledged from the nest less than a week after this video was taken:

Read more about our nest box installation at Summerhill Preserve (one of our nature preserves open by appointment) and the Kestrel population there in this June, 2014 blog entry.

American Kestrels Return to our Stroud Preserve

By Mike Coll, preserve manager

American Kestrel, Ron ZiglerThis year for the first time the walking trail through the “Bobolink Meadow” at our Stroud Preserve was closed to foot traffic during bird breeding season (April-August). This trail closure is one of a number of such closures aimed at protecting the breeding grounds of sensitive bird species. In this case the impetus for closing the trail was the breeding population of Bobolinks, a species that consistently nests in the grasses of this particular meadow. These ground-nesting birds can be negatively impacted by the proximity of humans and dogs (especially unleashed ones).

However, closing the trail appears to also have had a positive impact on another species in decline, the American Kestrel. Kestrels are also easily disturbed by humans and, although a box had been present for a number of years, I had never observed Kestrels nesting there until this year. The trail previously came almost directly beneath the box and likely was the reason they hadn’t used it.

Here is a video of the young birds (looks like 4) at just a few weeks old:

The continuing story of the Hildacy Screech Owls…

By Mike Coll, Hildacy Farm Preserve Manager

When I last wrote about the owls in the Hildacy nest box it was in March of this year and I was hopeful that the pair would attempt to breed again and would this time be more successful than they were in 2014. The pair in fact did make another attempt but unfortunately this year’s nest again produced no young.

The particulars of this year’s story begin with the female owl (the red phase owl) roosting in the box every day this spring except for one and on that day I observed the gray male owl in the box. I took this to be a sign that the pair had mated again and a week or so later the female began laying eggs.

However, unlike the previous year, this year I never saw the male owl again. The female, who should have been spending almost all of her time incubating the eggs (while being fed by the male), was instead forced to go out at night and hunt for herself. I once even observed her calling from the box, which is the opposite of the secrecy that birds usually display once they have laid eggs. My guess is that the male owl met an unfortunate fate. He may have been hit by a car or killed by a local Great-horned Owl, but it seems very unlikely that he would have abandoned his mate at such a crucial point.

When it became apparent that the male owl was not going to return, I made a somewhat futile attempt to act in his stead. Adult owls consume about one mouse per night, so I decided (after discussing the situation with wildlife rehabers at the Wildlife Clinic at the Schuylkill Center) that I would purchase frozen mice online (normally marketed to people feeding pet snakes) and supplement her diet the way the male owl would have. Each night I thawed out a mouse, waited for the owl to leave the box, and tossed the mouse into the box with the help of a long pole. It seemed like she started to expect these feedings and was able to spend much more time incubating and less time hunting. Eventually I decided that it would be less invasive to place the mouse out in front of the box and let her come grab it herself. Here is the slow-mo footage of her coming to get a mouse, captured with an infrared camera:

I continued feeding her for the better part of a month but the eggs never hatched and one day she simply abandoned the nest. I think it is likely that the eggs were either never actually fertilized by the male or that they were unable to survive the first few cold nights (before I started feeding her) when the owl was out hunting.

While this is obviously a disappointing result, I think it illustrates how precarious each year’s breeding cycle is. All factors must be accounted for in order for a species to successfully reproduce and many times this does not occur for one reason or another.

But, there is always next year and with that in mind I took the opportunity to replace the old box with a new more structurally sound version that also contains an upgraded HD camera.







The new camera has a larger bank of infrared lights, higher resolution and provides much more clear audio than the previous one.
After abandoning her nest, I didn’t see the owl at all during the summer. But a few nights ago I heard a Screech Owl calling from behind my house and then on 9/27 she spent the day roosting in the new box.

Hopefully, this owl will continue to use this box as a roost throughout the winter and then locate a new mate in the spring.

Chimney Swift Nest Tower at Hildacy

By Mike Coll, Hildacy Farm Preserve Manager

Chimney swifts are a unique species in many ways.  Swifts do not perch on branches as other birds do, instead they have evolved to cling like bats on vertical surfaces (except facing upwards).  They mate “on the wing” and then build tiny half-cup nests, adhered with their saliva to crevasses in interior walls, usually chimneys.  In the fall they gather into huge communal roosts before migrating to their wintering grounds in the jungles and caves of South America.  But perhaps the most intriguing attribute of chimney swifts has been their ability to adapt their nesting practices to accommodate the ubiquitous impact that human deforestation and development has had on available structures.

Prior to European settlement, the majority of eastern North America was old growth forest.  In that type of ecosystem there would be both very old trees and even older dead trees that were still standing.  In these huge standing dead trees would have existed suitable cavities for chimney swifts to nest.  However, since the 1600s virtually the entire continent has been deforested by humans.  In it’s place humans have built houses and buildings, many of which have chimneys.  Chimney swifts (only present during the summer months when chimneys are rarely used) were able to transition a large portion of their population to these brick and mortar substitutes.  While natural cavities are still used by some percentage of nesting chimney swifts, the vast majority of the current population is believed to reproduce in human made structures.

The problem is that brick and mortar chimneys are increasingly being replaced by smoother materials and/or covered by “pest guards”, both of which preclude swifts from being able to attach their nest to an interior wall.  Likely because of this trend and other challenges faced by aerial insectivore species, chimney swifts have shown consistent decreases in population.  Since 1966 a cumulative decline of 65 percent has been reported by the North American Breeding Bird Survey.  Among other warning lists, the species is considered a “common bird of steep decline” in the 2014 State of Birds Report.  Although overall population numbers have not yet decreased enough to put this species on a threatened or endangered list, the current rate of decline is profound.

In attempt to combat these declines, the Chimney Swift Conservation Organization has created these plans for a chimney swift nest tower as a substitute nesting structure.  With the help of volunteer Brian Bernero and my new assistant Gabrielle LeBlanc, we were able to construct a tower and hope to have it installed at Hildacy before the swifts return to search for nest sites in early May.

Below is my construction process from diagram to finish.  I plan to mount it to an existing tree stump as a base.  The only thing not shown in my plan is that the bottom panel has a square opening (about 10″x 10″) that is covered by a metal screen that will allow both airflow and nest monitoring.




The interior walls are T1-11 siding.  It is important to give a horizontal ledge for swifts to attach the nest.  Panels are attached with screws and exterior wood glue to treated 2x4x12’s



Brian next to one of the interior panels.   It is important for the nesting structure to have depth because swift nests are often found as far as 6′ down from the upper opening.



We then used treated 2x4x8’s to connect the walls.



Assembled interior



Because swifts want cooler temperatures at their nest sites, 3/4″ foam board insulation is added to the space between the inner and outer walls.  This tower will be placed in an area that is at least partially shaded and there may be some airflow drawn through it.



Outer walls added-  1/2″ treated ply.



I couldn’t find any suggested measurements for the upper opening but the pictures looked about like this.  The recommendations are just that the new opening is not more than half the size of the original opening; and that it is closest to the North facing side of the tower.  Again I think the purpose of this is to reduce temperatures in the tower by allowing less of the southern sun to penetrate the interior.



Swift stencils so that the birds (and other interested parties) will know what this thing is for.


A predator guard of metal flashing will also be added before the tower is put into place.

One somewhat disheartening aspect of this construction process is that at best, this 12 foot tall tower will support ONE PAIR of nesting chimney swifts.  While swifts often roost communally (especially just prior to migration), within each structure only one pair of swifts will build a nest.

If one does, I may be repeating this process in the future.

Owl box spring cleaning (and story update)

By Mike Coll, Hildacy Farm Preserve Manager

Almost every day this winter our resident female, red phase Screech Owl roosted in the box behind the spring house. This is the continuation of a story that has been ongoing for the past 5 years since I initially placed an owl box in that location (and then replaced it with a box that included a camera). For the first 3 years a gray phase male Screech Owl roosted in the box. Each spring he called from the entrance of the box but did not successfully attract a mate. This changed last year in early April with the appearance of a red phase female. Following her arrival the pair spent a few days together in the box. About two weeks later the female had laid a clutch of 3 eggs (laying one egg every other day). For the next 29 days the red female diligently incubated the eggs, leaving the box for only a few minutes each night. During this period her mate did the hunting, constantly bringing mice, frogs and insects to the box and feeding her.
However, for reasons unknown to me, none of the eggs hatched. It appeared that the female owl ate each of the eggs exactly 29 days (the expected incubation time) from the date that the eggs were laid (also eating only one every other day). I can only surmise that she somehow knew that the eggs weren’t viable (maybe they became cold?) and her instinct was to not let an available source of protein go to waste.

After the failure of the eggs, I didn’t see either owl for nearly a month. But at some point the red female began to roost in the box again and since then she has been a fixture there, usually sticking her head out to catch the last few rays of sun each evening before going out for the night.

In fact, the presence of the Red Owl has been so consistent that I haven’t wanted to disturb her by cleaning out the box. So when I looked at the camera yesterday and noticed that she was roosting elsewhere, I jumped at the opportunity to clean the box and do some repairs. Some of the metal flashing that prevents squirrels from climbing into the box needed to be reattached and I also added a bungee cord around the trunk to further support of the box itself.

The inside of the box was littered with 15-20 owl pellets and the feathers of what appeared to be a Downy Woodpecker, a Blue Jay and possibly some others. I scraped all of this out of the box and then added an inch or so of fresh wood chips. I then replaced a good number of the feathers that were in there because they seemed like an interior design choice that the owls had made. I first noticed feathers in the box just before the eggs were laid and I expect that she may use them as bedding.

This morning I was happy to see the female back in the box. I hope she likes what I did with the place.

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I expect that the male has remained in the area even though I haven’t seen him. We should know by the first few weeks of April if the pair will make another attempt at breeding.

Hildacy Farm Preserve: Red-shouldered Hawks

By Mike Coll, Preserve Manager


These Red-shouldered Hawks continue to be year round residents of Hildacy Farm Preserve. If the pair builds a nest again this spring it will be (at least) the fifth consecutive year that they have done so. While each nest has been in a different location, the meadows and wetlands of Hildacy have consistently been their hunting grounds, supplying them with the quantity of food required to feed not only themselves but a clutch of 2-5 young birds.

Eastern Black Swallowtail emergence at Hildacy

By Mike Coll, Preserve Manager

One of the things that I appreciate most about living on a preserve is getting to observe natural processes up close. I am constantly fascinated by the life stories of species that exist around us, which so often go unwitnessed. This year my wife noticed a Black Swallowtail (Papilo polyxenes) caterpillar feeding on the parsley in our garden. The larval stage of Eastern Black Swallowtails (like many insects) has very specific dietary requirements. These caterpillars will only feed on members of the carrot family, including Queen Anne’s lace (Daucus carota), dill, and parsley. As the caterpillars grow, they move through various stages, called instars. Each instar is different in appearance, and the caterpillars sheds their skin four times as they move into the next instar.

This individual is in it’s second or third instar.

Black Swallowtails complete multiple generations each year. Because it was early in the summer when we found this caterpillar, I knew that it would complete its life cycle this season and that the resulting butterfly would then lay more eggs and go through at least one more cycle before winter. The final generation of this species each summer remains in chrysalis throughout the winter (unlike Monarchs, which migrate) and emerges the following spring.

I placed the caterpillar in an insect container, supplied it with some dill and parsley clippings from the garden, and waited to see what would happen next.


This is a fully grown Black Swallowtail caterpillar (4th instar). At this point, I made sure that there were a few sticks in the enclosure so that it would have something to anchor its chrysalis to. I also continued to give it fresh parsley every few days because it obtains both food and water from vegetation.


Within a week, the fully grown caterpillar created a chrysalis on one of the branches. Swallowtail chrysalises always have that one little spider web-like string attaching it to the branch. Amazingly, in the case of individuals who overwinter in chrysalis, that tiny string remains intact throughout the many months and harsh weather between the fall and spring.

During their time in chrysalis, Swallowtails essentially digest themselves and the fat stores that they have built up during the larva stage and reconstitute the elements into a new form.


Just a few weeks later, the chrysalis split open and this butterfly emerged. It has been shown that certain memories created during the larval stage are carried over into the butterfly stage in some species.  So, at least in some ways the consciousness that was the caterpillar continues to exist when it becomes a butterfly.

While its obvious that a butterfly’s consciousness is far different from ours, I couldn’t help but wonder what possible view of the world this butterfly could have after inhabiting such a completely different form just a few weeks earlier. When the above picture was taken it seemed like she had not yet realized that flight was now possible.


After a few minutes, the newly emerged butterfly took off and landed on a native perennial a short distance away. This butterfly can be identified as a Black Swallowtail by the two rows of yellow dots along the wings (as opposed to a dark-morph female Tiger Swallowtail, which only has one row). It is a female because male Black Swallowtails have much larger yellow dots in a similar pattern.

In its adult form, the Black Swallowtail butterfly will feed on the nectar of a variety of flowers and hopefully mate and lay more eggs on one of the carrot-plants that can support the next generation of caterpillars.

One recommendation I have for anyone who finds a caterpillar and would like to watch its metamorphosis is to make sure that you have adequately identified and researched the species that you find. Because each species has very particular requirements for its survival, failing to provide the correct vegetation or habitat will not yield good results. There are plenty of resources online that can help with identification of caterpillars and butterflies. Lately, I have found this site to be good source of info. Despite being from northern Virginia, most of the species are the ones I see here in eastern Pennsylvania.

Kestrels at Summerhill Preserve

A new Kestrel nest box at the Summerhill Preserve successfully attracted it’s target species in the first year.   The box was mounted on a natural cedar post by FON volunteer Brian Bernero.  Installed, the opening of the box sits approximately 14 feet above the ground in a warm-season grass meadow.  I wrapped metal flashing around the post to prevent predators from climbing up into the box.


A pair of Kestrels found the box almost immediately in early April.  I observed the male sitting on the box with the female in a nearby tree.

A few weeks later towards the end of May I reached a camera on the end of a pole into the box and took this picture.

The fact that the female (pictured) did not leave the box when I approached it told me that she was likely incubating eggs.

A few weeks later on 6/12 I returned to take this picture showing some newly hatched falcons, probably 7-10 days old.


This week (on 6/25) I returned again to the box.  As I approached I could see the head of one of the young birds poking out of the hole.


Less than 30 days after hatching, young Kestrels weigh as much as their parents.   These 5 fledglings have grown most of their flight feathers and are nearly ready to leave the box.  Once they leave the nest their parents will continue to feed them for a number of weeks as they learn how to fly and become effective hunters.  All of them must race to become self sufficient before the fall when they will most likely attempt their first migration.

Hildacy Preseve: Red Owl lays eggs

By Mike Coll, Preserve Manager

About 2 weeks after the Red morph Screech Owl first arrived at the box she began laying eggs.








Screech Owls generally lay a clutch of 2-6 eggs at a pace of one egg every other day.  As of yesterday when this video was taken she has laid 3 eggs.

So far both owls have continued to stay in the box during the days.  As night falls the male owl leaves the box to hunt and periodically returns to feed the female, who spends most of the night incubating the eggs.  In the video it seems like the male feeds her something small like an insect, but on other occasions he has returned with mice or frogs from the nearby wetlands.  The female does leave the box occasionally during the night, possibly to get a drink of water or stretch her wings, but she is never gone for more than about 20 minutes.

Screech owls incubate their eggs for approximately 4 weeks before they hatch.  If this holds true, the young owls should emerge during the 3rd week of May.

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Hildacy Preserve: Screech Owl pair

By Mike Coll, Preserve Manager

Two days after my first ever sighting of a red morph Screech Owl I was pleased to see both the grey and red morph owls together in the box.  It is now my view that the red morph is a female and the grey morph is likely the same male owl that has been roosting in the box throughout the winter.

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You can see in this picture that the head of the lighter colored owl (red morph) is slightly larger than the grey owl, again suggesting that it is a female.

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The pair stayed in the box all day yesterday, alternately preening the other’s feathers.  Today only the female owl has returned to the box, but I think that is still a hopeful sign.




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