Richard and Diane Van Vleck Personal Pages
The Home Habitat

The Continuing Saga of Barn Swallows and Black Rat Snakes

The 2019 nesting season brought both successes and failures in the barn swallow colony room as well as continued drama courtesy of that extraordinary serpent, the black rat snake.
Black rat snake grabs barn swallow nestling
Three large black rat snakes caught attempting to enter the barn swallow room
A chronological list of events
May, 2019 - Two pairs of barn swallows and a pair of Eastern phoebes nested in the swallow room. All three nestings were successful and uneventful, fledging 5 and 4 swallows and 4 phoebes. The phoebes used a swallow nest cup rather than their usual nest site on top of a log beam. The wooden nest cup containing an old swallow mud nest was appropriated by the phoebes and lined with shredded plant fibers. The edge was decorated with small mats of moss, as usual for this species. It will be interesting to see if the phoebes use this same nest cup next year.
Eastern phoebe feeding young in barn swallow nest cup
Eastern phoebe nest in barn swallow nest cup

The phoebes and swallows do not interact with one another, even during busy feeding times. In previous years, phoebes and swallows have occasionally nested within 4 feet of each other. The phoebes are cautious in approaching the nest, making several stops along the way, and then quickly feeding the nestlings, remaining at the nest only 3 or 4 seconds. The barn swallows are much more relaxed, often waiting after feeding to receive a fecal pellet or even hanging around for several minutes, seeming to be admiring their progeny. But, during prime feeding times, the male and female arrive together, quickly delivering their prey and flying off together. In the evening, they often scoop up enough insects right in the barnyard and continually fly to and from the nest, making sure that everyone’s belly is full before darkness sets in. Then, the big brown bats take over. The bats, always first, upon leaving the barn, head for the creek, but later, spend hours in the swallow room. They assemble in a group to roost on the side of a specific joist. The largest numbers of bats are present from 10pm until 5:30am. During this time, individuals will occasionally fly off to catch one of the many moths flying about the room and then quickly return to their night roost. I had no idea how much time the bats spend resting or sleeping during the night until one of the swallow nest cams recorded their night roost in the background. This roost was also on one of the smoothly planed joists. It appears they are not intimidated by the black rat snake. In 23 nights of video recordings of their roost site in August, no snake appeared. And, unlike swallows, the bats are not disadvantaged by darkness.

Big brown bats in their night roost in the barn swallow room
Eptesicus fuscus in the night roost

May 27-29 A cardinal nest hidden behind vines on the milk shed wall was predated, most likely by a black rat snake. I had observed the female cardinal leaving the nest location several times, but could not see into the nest itself without disturbing the vegetation. However, carefully slipping a cell phone through the vines enabled photographing the nest and its three young occupants. A video camera was set up to monitor the site, but even the return of the cardinals was not recorded since they entered off to the side and were also completely hidden by the vines. Video recording was discontinued and the nest was checked each day using the cell phone. Three nestlings were present on May 27, two of these were missing the next morning and the third was taken the night of May 29. A black rat snake could easily have reached the nest by climbing up the wall without disturbing the vines or the nest. Visually detecting the perfectly hidden nest would have been completely unnecessary for the snake.

The cardinal nest habitat
Cardinal nest with three nestlings
June 6 - Three large black rat snakes were caught together in netting trying to enter through a swallow room door. While the door was sealed, netting was placed on the outside of the screen to detect any attempt at entry.
Three black rat snakes

July 2019 - Both barn swallow pairs renested for second broods. Each pair used a different nest cup for the second brood. One pair moved to the rear of the room, laying 5 eggs. The other pair moved to a cup within 8 feet of their first nest in the front of the room and laid 4 eggs.

July18 - A female black rat snake was caught in netting at another swallow room door. There were ten eggs under the snake plus two not yet expelled. I placed the twelve eggs in a container and carefully covered them with damp saw dust. They were left in the swallow room where the temperature is fairly constant, but likely too cool. However, this is apparently where the snake intended to deposit them. The sawdust was kept moist during incubation.

Female black rat snake with eggs

July 19 - The barn swallow nest with 4 eggs was predated. All 4 eggs were gone. No doubt, a black rat snake was the culprit.

July 20 - An infrared lighted camera and DVR were set up for 24 hr monitoring of the remaining barn swallow nest with 5 eggs. The very first night, a black rat snake climbed the rubble wall twice to reach the joist where the nest was located, but did not venture out on the joist toward the nest. It appeared to be unable to cling onto the smooth surface of the joist. The female swallow instantly flew off in the dark, obviously aware of the snake. Luckily, this nest cup is mounted on a smooth and square joist. Many of the joists are sawn flat only on the top and have rounded and rough surfaces on the sides, allowing a snake to wedge itself between the rounded side and the floor boards above.

Aug 13 - A black rat snake again attempts to reach the swallow nest from the rubble wall and again cannot negotiate the smooth sides of the joist. Now the nest has 5 nestlings almost ready to fledge. Later in the night, the snake reaches the nest from the opposite side. Even though the joist was smooth and flat, an electric wire running along the other side of the joist allowed the snake to move out along the wire and coil around a lamp fixture close enough to reach the nest. One nestling was grabbed from the nest and the others fledged into the dark. They were observed being fed the next morning. For a second brood, 4 out of 5 fledging is not bad. Was the snake’s approach from the opposite end and opposite side of the joist and then coiling around the light just dumb luck? Or, did the snake have a plan?

Black rat snake approaching barn swallow nest
Black rat snake striking barn swallow nestling
Black rat snake pulling barn swallow from nest
Black rat snake swallowing barn swallow
Barn swallow nestlings fleeing from nest after snake attack
Black rat snake swallowing barn swallow nestling
Aug 30 – A bait cage with a mouse was set up in the swallow room with bird netting surrounding it and monitored with video. No snakes were seen during a week of monitoring. Note the white footed mouse om the pvc flange on top of the cage in the photo. It would visit the cage each night, having no problem passing through the layers of bird netting. I don’t know if it wanted company or a bit of lab chow purposely left for it.
Bait cage to attract black rat snake

Sept 8 – A large black rat snake was caught in netting under the front porch.

Oct 12 – one of the snake eggs collected on July 18 was opened for inspection It was grossly underdeveloped and long past normal hatch date.

Black rat snake embryo
Oct 19 – The remaining snake eggs were opened. The embryos were slightly longer than last week and there was less yolk remaining. However, at hatching, rat snakes average 13 inches. These were half of that.
Black rat snake embryos

Oct 25 ¬– While priming the oil furnace fuel line in our basement, I happened to notice a section of a black rat snake’s body protruding from insulation that had been stuffed between the joists along an outer wall. It was slowly moving, apparently bothered by my noise. After I finished closing off the fuel line, I looked up again and the snake was out of sight, leaving only the two small holes in the insulation where it had moved out and then back in again.

Dec 22 – I finally checked the basement for the snake seen earlier. It was not behind the insulation. A 3 inch wide space behind the log sill ran the entire length of the wall except at the chimney. Using a video inspection camera with a 30’ reach, I was able to check this otherwise inaccessible space along the wall and around the corner to the front wall. Although I could not see any opening to the outside, there likely is one. Years ago, when I had run an electric wire out this wall and under the front porch, I found several groundhog holes under the porch which I now realize might be ideal snake hibernation sites. A black rat snake was trapped under the porch both this year and last. Also, I could not check half of the front wall with the video camera because the interior was plastered up to the floor boards. There are many perfect options for a hibernating snake and, likely, many more that I have not found. The snakes are welcome in the basement, just not in the swallow room.


Barn swallow nest cups
A new barn swallow shelter
2019-2020 barn swallow nesting
2012 barn swallow nesting
2012 barn swallow prey cam
Using artificial nest cups
2015-2016 barn swallow nesting
Attracting barn swallows
The Barn Swallow
barn swallow basics
Transplanting a barn swallow nest
2001 testing nest cups
barn swallow shelters

2022 update - Return of the barn owls
2021 Chimney Swift tower success!!!
2020 Barn Swallow nesting
Barn swallow nest cups
2019 Barn Swallows and Black Rat Snakes

2018 - The Barnyard Balance of Nature Goes Awry
Black rat snakes vs barn swallows, Northern flickers, kestrels and others

2018 Purple Martin preference for clam shells
2017 - Return of the Monarchs!
2017 Purple Martin prey photos
2010 - 2016 Northern flicker nestings
2014 house wren gourd use
2014 - A dramatic loss of many types of insects
2019-2020 Purple Martin nesting
2014 barn owl nesting - prey study
A new barn swallow shelter for 2013
2010 barn owl nesting
2010 Update
2016-2017 Kestrel nestings
Starling traps
Using blinds in the home habitat
Providing perches for birds
Providing snags for wildlife
The ugly young maple
2001 - 2013 nest cams
Use of tomato cages as hunting perches by insectivorous song birds
Vultures, beetles and the resurrection of life

Species of interest in our yard - photos and articles
barn owl American kestrel purple martin barn swallow Eastern bluebird
tufted titmouse Eastern phoebe yellow shafted flicker tree swallow chimney swift
house wren big brown bat Carolina wren brown thrasher catbird
Willow flycatcher
cedar waxwing Northern mockingbird
Blue-gray gnatcatcher
turkey vulture
Yellow warbler Acadian flycatcher

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