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A New Management Plan Works for Prothonotary Warblers
Dick Tuttle

 

After the 2010 nesting season, I decided to try pairing nest structures (nest jars made of four-inch PVC drainpipe and nestboxes made of plastic or wood) to accommodate Prothonotary Warblers and Tree Swallows. My project is located along the western shore of Alum Creek Lake south of Kilbourne in Delaware County, Ohio. By 14 April 2011, I had installed nest structures that stood above the lake at seventeen locations. One additional pair and four singles stood along the opposite shore along Hogback Road. At each paired location, two nest structures stood within five yards of each other. In 2010, all of my nest structures had 1-1/4-inch entrance holes, but by 2011, I had bored out half to 1-3/8" to make it easier for Tree Swallows to enter their nest chambers. I had also patched the remaining entrances down to 1-1/8" to admit warbles while shutting out swallows. One of each made up pairs that stood above the lake.

The middle two nest structures have 1-1/8" entrance holes that will admit Prothonotary Warblers but will shut out Tree Swallows. The
outer two nest chambers have 1-3/8"
entrances that will admit both species
Three six-day-old Prothonotary Warblers are the latest family of 2011 with their first egg laid on July 5. They left the nest on July 31. This July 2008 photo by Mike Maier shows that a Prothonotary Warbler in a 1-1/4” entrance could easily negotiate a smaller 1-1/8” opening.

To better match nest sites with birds’ behaviors, I faced the warbler boxes toward the shore since yellow swamp warblers hunt insects from wooded habitats, and for aerial-feeding swallows, I pointed boxes and jars with larger entrances toward the lake. I tried to place pairs near trees that had toppled or leaned into the lake in order to maximize shade during morning hours. Since the shoreline along my project is the base of a steep, wooded ridge (with a recreational horse trail), all nests are shaded during the afternoons.

As expected, Tree Swallows nested in every nest chamber that admitted them, raising 77 young from 20 of 23 nest attempts, and I was extremely pleased when 33 warblers fledged, surpassing all my expectations. The 2011 yield was 2.35 times greater than 14 warblers produced in 2010. In 2011, females completed nests at seven of nine locations where males had added moss to nest chambers. Among 41 warbler eggs laid, 36 (87.8%) hatched and 33 (80.5%) fledged. More than nine of every ten hatchlings (91.7%) matured to fledge. The prothonotary’s nesting season, from the first egg laid to the last nestling fledged, lasted 82 days from May 11 through July 31. The latest first egg date was July 5, the latest ever for my prothonotaries. In the future, I will wait until after July 5 before I start removing nest jars for winter storage so I don’t deny a nest site to any late nesters.


The idea of pairing nest structures specifically made for warblers next to designs built for swallows was applied to lessen competition between the two species while adding aerial protection for warblers’ nests. Swooping swallows will defend all nests within a fifteen-yard radius from their own. Hoping that Tree Swallows would act as deterrents against hawks, woodpeckers, and egg-piercing House Wrens was one objective of my plan while offering smaller entrances that protect warblers from swallow competition was another goal.

 
At the beginning of the 2011 nesting season, the plan worked as planned at four locations where warblers chose to nest in chambers with smaller openings, while swallows chose the larger entrances. Nest histories for both species at three locations were synchronized with only two, two, and five days, respectively, separating first egg dates between the neighboring species, and peace reigned at these locations. Of course, there are always those birds that do not go along with the plan. Warblers chose to nest in three structures with larger entrances meant for swallows, and one family paid a fatal price for its bad choice.


One of three warbler nests in nest jars with “swallow entrances” had hatched all six of its eggs. I was on a mission to attach leg bands to its nestlings on June 6, and as I floated my canoe toward the warbler nest, I saw a parent warbler charge and chase a Tree Swallow away from its nest jar. When I opened the jar, I found only five nestlings, and one was dead. The dead nestling had two small open wounds on its head that barely tore its delicate skin. Another live nestling showed a swollen eyelid. As I examined the siblings and went about attaching their leg bands, I looked up to see two swallows perched on the same limb within ten feet of me, staring and stalking the warblers’ nest jar. When all the evidence was considered, the swallows’ one-man jury found them guilty of the crime. The Tree Swallows’ behavior told me that they were determined to nest in the jar inadvertently claimed by the warblers.

 
I looked down to the floor of my canoe where the warbler nestlings had snuggled into a warm clump on my pack. They all wore their new leg bands and I knew what I had to do to insure their safety. I reached into their jar and gently removed their moss nest and placed it beside them. I then proceeded to switch the nest jars by trading their places on their mounting pipes. Once the jars were in their new locations, I placed the prothonotary’s moss in the jar with the smaller, safer entrance. The jar with the largest entrance hole now stood where the swallow-excluding nest had once been. I returned the banded nestlings to their moss nest at their same location, but they were now safe and free from murderous swallows. As I paddled from the site, I paused to see a yellow parent entering its new, smaller entrance to feed its nestlings. And, yes, I forgave the determined swallows, and they went about raising four of their own in the nest jar that had temporarily housed warblers. Mission accomplished.

Some might argue that it is best to make all entrance holes 1-1/8" and exclude swallows altogether, but I want Tree Swallows to keep devouring the more than 300,000 flying insects that each family consumes as they occupy their nestbox. I will continue to do my part for both species that commonly shared habitats during the era of abundant wetlands maintained by beavers hundreds of years ago when only Native Americans inhabited our continent. For the future, I will carry tools and a rivet kit so I can patch down entrances at any nest sites where warblers have claimed the “wrong” nest jar, etc. Also, I will also include extra “swallow-friendly” nest jars in my canoe in order to keep the aerial-feeders in the game.


Each of two locations produced two broods of warblers during the 2011 season. At one spot, a jar with a swallow entrance raised three warblers, and then raised a second brood of four in the jar it was paired with that had a smaller entrance designed for warblers. Unlike the murderous swallows described above, the swallows at this location had been patient enough to wait for the first brood of warblers to fledge before they “moved in” and raised four of their own.


At another location, warblers raised consecutive broods of five and three in the same jar as swallows used the neighboring jar to raise their family at the same time as the warbler’s first brood. Close by, a large, dead tree had fallen into the lake and its bare crown became a community gathering place for Tree Swallows and Northern Rough-winged Swallows throughout the summer, adding more protection for the warblers nesting there.


Two families of Carolina Chickadees raised five and six young. One of the chickadee families took advantage of a paired nestbox with a warbler entrance. The other chickadee family nested in a nestbox that was not paired and stood alone along the eastern shore. Once chickadees fledged, the only nesting House Wrens moved in and raised five. Another wren was responsible for the only warbler nest failure, but only after paired swallows had fledged, leaving the late-nesting warblers unprotected. The wren only left a few sticks before it was time for me to remove the nest jars for winter storage.

 
The effort to band my project’s prothonotaries demands that I make more canoe trips along the project’s one-mile route. Because of the physical demand, I was beginning to question whether I should continue to band warblers. Then, I received a report from the Bird Banding Lab that a Prothonotary Warbler banded by me on the Delaware Wildlife Area on 10 July 2010 had been found at South Lake, Indiana, five miles west of Terre Haute. One of five nestlings that I had banded from jar-5 had flown south to winter in Central or South America and returned near the Wabash River, 240 miles from its natal nest. Jean Cottrell of Terre Haute had found the bird dead in a bluebird nestbox on 13 May 2011; a House Sparrow had killed it. Ironically, the bird’s bad luck renewed my spirit to keep banding my prothonotaries. Now I know that my feisty, little warblers are dispersing to far away lands where, hopefully, fellow conservationists will welcome them with effective management plans.


Conserve on, Dick Tuttle