Productive Golden Swamp Warblers

Prothonotary Warbler center - Photo Earl Harrison

In 2004, my effort to raise Tree Swallows produced a family of Prothonotary Warblers, Protonotaria citrea, that fledged two from a clutch of five eggs. Since that first of sixteen warbler seasons, 333 prothonotaries have added their golden beauty to our world. The 2019 season was the most productive with 39 fledged, which is five more than the second most productive season in 2012. The season was highly successful, despite an overabundance of rain and high water.

During the 2019 season, one family of prothonotaries fledged three from a nestjar on the Delaware Wildlife Area where I have five nestjars suitable for warblers. Nestjars are made from four-inch wide drain pipe. Most nestjars have wooden floors and the roofs are made from plastic railing bolted to a removable cap.

Paired Nestjars for Prothonotary Warblers

Paired nestjars work well to house nesting Tree Swallows and Prothonotary Warbler

The north end of Alum Creek Lake is home to 45 nest structures composed of eight nestboxes and 37 nestjars. Most of the structures are paired at five or more yards apart with one having a 1-1/8 inch wide entrance hole to admit warblers, while its mate has a 1-3/8 inch entrance for Tree Swallows. Two independent boxes have 1-1/2 inch openings to admit Tree Swallows or bluebirds and stand near Hogback Road. The wildlife management objective is to have nesting swallows defend their nests from House Wrens, and inadvertently protect nesting prothonotaries in the process.

So, how successful was the 2019 nesting seasons at Alum Creek Lake? Prothonotary Warblers had eight successful nests after 14 attempts for a 57.1% success rate. They laid 62 eggs, 37 (59.7%) hatched, and 36 (58.1%) of the eggs developed to fledge. Once hatched, 97.3% of the hatchlings grew to fly from their nests.

Of the six warbler nest failures, four nests were victims of House Wrens. Studies have revealed that in most cases when wrens use their sharp bills to spear eggs of other species, the male wren is the villain as he tries to claim nest sites, and it only takes seven seconds per egg for him to puncture and flip the victim’s eggs from the nest.

In two other warbler nests, only one egg of four hatched and it failed to fledge, while all four eggs failed to hatch in another nest.

Prothonotary Warbler Hatchlings

Four warbler hatchlings out of five eggs await 10 – 12 days to fledge.

The prothonotary’s first egg date for 2019 was May 13 and the latest fledging took place around June 24 for a 43-day season. There were no second clutches. In 2016, I analyzed data from 55 nests and the earliest first egg was laid on May 4 and the latest fledging event took place on August 9 for a 98-day season. So, the 2019 season was less than half as long, 43.9%, than the historic length of the warbler season. This is easy to explain once the weather history is examined.

Before I installed my first nest structures at Alum Creek Lake in 1998, I consulted with the US Army Corps of Engineers to find the historic lake level during its highest flood. The Corps’ job is to use their dam to control downstream flooding and that creates their lake. Since 1976, the lake has risen nearly six feet above its summer pool of 888 feet above sea level, so I had to design nest structures that offer nest cavities more than six feet above the lake’s summer pool.

My boxes are attached to sleeves of plastic water pipe five-feet long that slide up and down on lengths of steel water pipe or electric conduit, all near the lake’s shore. A hose clamp holds the nest cavities more than six feet above the lake and can be easily disengaged to enable the box to be lowered for monitoring.

Boxes and sleeves are stored at my home during the off-season while the pipes remain on sites all year. Maintenance and monitoring are accomplished from my twelve-foot-long canoe powered by my kayak paddle.

Every morning before breakfast, I check the Corps’s website in Huntington, West Virginia, to record water levels at four sites, including Alum Creek Lake. Heavy rains in June caused the lake to reach 5.1 feet above summer pool on June 22. None of my boxes were inundated, and all successful warbler nests had fledged before, or just after, high water levels. Unfortunately, all four warbler egg clutches that started after mid-June failed.

The high water levels would have caused insects to crawl up vegetation to seek dry habitats, making them more vulnerable to birds seeking insects within the same surroundings. As I attached U.S. Fish and Wildlife Service leg bands to warbler nestlings, they all felt healthy and well fed. Of course, the flooding would have interrupted many life cycles, and along with easier harvesting by birds, would have lowered subsequent food supplies to explain why some warbler nests failed due to what appeared to be abandonment, etc.

The good news is Tree Swallows at Alum Creek experienced the most successful season of all my trails in Delaware County. All 22 swallow nest attempts were successful. After 109 eggs were laid, 105 (96.3%) hatched, and 93 (85.3%) of the 109 eggs developed to fledge. After hatching, 85.6% grew to fledge.

House Wrens also raised young from all of their nests. Nineteen nest attempts produced 101 eggs, 95 (94.1%) hatched, and 89 (88.1%) fledged. Once eggs hatched, 93.7% of the wren hatchlings grew to launch independent lives.

Five hundred years ago, Prothonotary Warblers would have had a furry friend helping them deter nest usurpations by House Wrens. Beavers were quite prevalent before the European fur market arrived. By 1830, beavers had been extirpated from Ohio, and their ability to snip, carve, and prune wren habitat back from the shoreline had disappeared.

Today, beavers are returning, but their populations will never rebuild to historic levels even though they are showing their true value in creating healthy wetland worlds across North America. In the meantime, I’ll do my best, with the help of territorial Tree Swallows, to help our golden swamp warblers to multiply. Conserve on!