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Posts categorized Hildacy Farm Preserve.

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.

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.



Hildacy Preserve: Red morph Screech Owl

By Mike Coll, Preserve Manager

Yesterday I got an answer to a question I had been wondering about for a few years:  Is it always the same Screech Owl that I see roosting in my owl box?












The answer, apparently, is no.

Screech Owls come in two different color “morphs” or variations- grey morph and red morph.  Previously I had only observed the grey variety (right) but yesterday the head of a red morph (above) was peering out of the box, giving me the first clear indication that the box is being used by more than one individual.

Curiously, this new owl fell right in line with the patterns of the other owls that have used the box.  In fact I had observed a grey morph owl in the box every day for the past few months until this red one took up residence without even a single day break.  Also, the red morph sat in the box opening at dusk, flew out just before dark, returned at some point in the predawn hours and is currently sleeping in the box just as every other Screech Owl that I have observed there has done.  Were it not for the obvious difference in plumage I would not have even suspected that a new owl had moved in.

With breeding season for Screech Owls virtually upon us, the implications of this changing of the guard are unclear to me.  I have assumed previously that the owl(s) I was seeing was a lone male who had not yet found a mate.  This notion was supported in part because last spring I could hear the owl calling from the box- as a lone male would.  But knowing now that it has been more than one owl (possibly many different individuals) some residents could have been female as well.

I wonder if this new owl took the box by force in a territorial battle or if the box was abandoned willingly by the previous resident.  I wonder also where the owl that was there last has gone now.  And I wonder if any of these owls will choose to breed in the box in the upcoming months.  As is often the case, an answer to one question only serves to create a host of new questions yet to be answered, keeping me continually fascinated by the secret lives of these nocturnal creatures.


Hildacy Farm Preserve: Nest box work

By Michael Coll, Hildacy Farm Preserve Manager

As April approaches, it is the last chance to prepare nest boxes for the return of migrant species.  Throughout the next few months, breeding pairs will be searching for nesting locations and attention to detail within each nest box installation can be the difference between successfully attracting the target species and simply placing a wooden box in the landscape.

The first new box that I put up this year was a Wood Duck box near the restored wetlands at Hildacy Preserve.  The box was well constructed by a volunteer and on the opening now sits more than 8 feet off the ground.  I have used two wraps of metal flashing around the wooden post to hopefully prevent intrusion into the box by nesting squirrels and potential predators.


My choice of location for this box was motivated by two separate ideas.  The first is as a potential nest spot for Wood Ducks.  Each year around this time I observe a few Wood Ducks visiting the wetlands (in fact there is a pair there now as I write this).  The birds are present for a few days or weeks, most likely feeding on the abundant plant life and insects in the wetlands, and then go somewhere else for the bulk of the breeding season.  I suspect these wetlands might be just a bit too busy for Wood Ducks to feel secure.  Different species are affected differently by the presence of humans and Wood Ducks tend to prefer a more secluded setting than, say, Mallards, which often don’t seem bothered by people at all.  However, it is also possible that these passing ducks haven’t stayed because there were no suitable cavities in which to nest.  If this is the case then perhaps they will make use of this new box.  I placed it as far from the main walking paths as the area allowed.  The placement was also determined by the idea that it could be easily observed.  I have put other Wood Duck boxes up in considerably more secluded locations on Hildacy and in fact these locations are so secluded that I have not properly monitored them and so I do not know if they have been used!

The second purpose for this box is as a possible secondary home for my resident Screech Owl.


I have read that breeding Screech Owls will sometimes seek out secondary roosts near their nest sites.  Perhaps when a small box becomes full of young fledgling owls it is nice to have somewhere nearby for the adults to sleep.  Because Screech Owls will sometimes use Wood Duck-sized boxes, I thought that placing this new box in a direct line of sight with the existing owl box could possibly serve that purpose (assuming it is not occupied by Wood Ducks).

For the past two years, a Screech Owl has roosted throughout the winter in a box about 100 yards away.  I have a working camera in the box and, as I write this, he (I believe it’s a male) is sleeping the day away inside.


Each spring when breeding season arrives for Screech Owls, I have heard the male calling from the opening of the box, but I have never observed a mate.  A few weeks later, the owl leaves the box (presumably to breed somewhere else) and doesn’t return until the fall. I hope that this year the presence of a secondary roosting spot will change this pattern and convince a pair to nest.

Another project that I crossed off my list recently was to increase the height of my bat box. Originally this large, heavy (sail like) box was attached to a 12’x4”x4” post that was set into the ground with cement.


With a few feet of the post buried in the ground, the opening of the box (which is on the bottom) was barely more than 7’ high. The recommended height for bat boxes is no less than 10’ and higher is preferable. I had hoped that placing it on a slope would help to make up for this, but after seeing it go vacant last year I decided to cut the existing post and add a second 12’ post, attached by carriage bolts at the top and bottom. This addition raises the opening of the box to over 13’.


Hopefully, this will make the box more attractive to bats since its current location hits nearly all of the other recommendations for placement including: distance from trees (25 ft), proximity to water (stream and wetlands), good sun exposure, and south facing in an area where bats are regularly observed.

Last year was a banner year for Kestrels at Natural Lands Trust’s preserves with nesting pairs in boxes at both Gwynedd Wildlife and Hildacy Farm Preserves.  I am hopeful that the Kestrel box at Hildacy will soon be inhabited again by these small, brightly colored falcons.


In that aim I have cleaned the box that was used last year (including scraping the interior walls, which the fledglings seemed to have painted white!) and replacing the bedding with new wood chips.

In addition I have added another Kestrel box at our Summerhill Preserve. I have previously observed breeding Kestrels on this preserve (I saw fledgling birds but never found the nest site). However, last year–possibly due to a nearby “forest cleanup” that removed some old standing dead trees–I did not see any young birds. It seems likely that the pair’s nesting cavity was destroyed, which makes Summerhill an ideal location for a box. With any luck, the pair will find the box and breed successfully in the next few months.


The box was constructed by Force Of Nature volunteer Brian Bernero, who mounted it on a natural cedar post. To extend the length of the natural post we bolted it to a mostly buried 4”x4” making the final height of the box’s opening more than 12’ off the ground. Metal flashing was again used as a predator deterrent. The box faces south and is in a warm-season grass meadow that is rich with prey and removed from human disturbance.


The last of the nest box preparations were performed by other members of our Force Of Nature team who have cleaned out all of the 44 Eastern Bluebird boxes at Hildacy and Summerhill. While many of these boxes are used each year by Tree Swallows, Chickadees, and House Wrens, bluebirds continue to find boxes to nest in as well. Last year, volunteer monitors reported seven successful bluebird nests at the two preserves yielding 31 fledglings. This year, I will change the location of the boxes that were dominated by House Wrens in an effort to discourage them. I will also be continually mowing small areas around some of boxes that are in the warm-season grasses. It is possible that by keeping the grass height lower, more bluebirds will return to attempt a second brood. (Download our guide to Eastern Bluebird nest boxes here.)

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Carolina Wrens Fledge

Mike Coll, Hildacy Farm Preserve Manager

For the second time in three years, a pair of Carolina Wrens made a nest in a little ceramic birdhouse that my wife crafted and hung by our back door at Hildacy Farm Preserve (we live on the preserve).  Carolina Wrens can be differentiated visually from House Wrens (which are also very common) because of the prominent white stripe above their eye.

Here the adults are feeding their young:

Then the big day came and the young birds made the jump to the outside world!

A few minutes later, the whole brood was sitting in a nearby shrub and the parents were flying around feeding them. All of the young had fluffy feathers around their heads and short tails.




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