Alum Creek Prothonotary Warbler Project: 2013

Since 2007, I have offered nestboxes and nestjars to golden swamp warblers nesting along the most northern shores of Alum Creek Lake south of Kilbourne in Delaware County. Nestjars only resemble jars since they are made of four-inch PVC drainpipe with roofs made of PVC fence railing. The good news is that 149 warblers have been raised from these offerings, but the bad news came in 2013 as only 26 fledged compared to 34 raised during the previous year’s season for a 23.5% reduction in production. Wildlife managers, whether professionals or amateurs like myself, like to make progress and we sometimes take a downward trend personally. As I have in the past, I managed to add leg bands to all warbler nestlings to make it easier for researchers using mist nets, or conservationists finding them dead or alive in nestboxes, to reconstruct their histories. In order to record accurate nest data needed to plan timely leg banding events, I had to launch my canoe 13 times from the guardrail along Hogback Road.

Forty-five nest structures make up my project with three boxes standing along Hogback Road. Most of 38 nestjars are found along the opposite shore and are paired. One jar of each pair has a 1-3/8-inch entrance for Tree Swallows and the other jar has a 1-1/8″ opening for the target species, Prothonotary Warblers. Paired jars are spaced five or so yards apart so Tree Swallows defending their nest from their own kind and other species will inadvertently defend their neighbors’ investment. Four experimental nestjars designed to deter woodpeckers were added this year for the first time and were accepted by House Wrens and warblers.

Paired nestjars work. Of six successful warbler nests, five raised their families while Tree Swallows did the same in adjoining jars. Swallows might also have helped the sixth successful warbler nest in a very strange way. The first egg of the season’s latest warbler nest was deposited on July 14, the latest first-egg-date ever in my experience. The “July 14 nest” was constructed in a jar that had raised six swallows and stood empty since the earliest days of June, but that is just part of the story. The front of the nestjar was hideously caked with fecal droppings after swallow nestlings had backed upped to the jar’s entrance to defecate into the outside world. Did the appearance of this jar deter House Wrens? I certainly don’t have an answer to my own strange question.

House Wrens were true spoilers in 2013. I have never seen so many wrens on all of my trails. I monitor 408 nest structures in Delaware County and wrens fledged 342 young in 2013 for a 57.6% increase over 2012’s total. Wow! Wren survival over the winter and during their migrations must have set records of their own. Wrens were everywhere. Unfortunately, wrens evicted eggs from seven warbler nests and that brings into focus that my project is not in the best of warbler habitats.

Beavers make the best habitats for prothonotaries. Castor canadensis builds dams and plugs them with mud scraped from canals as they expand their wetlands. Water behind beaver dams rises to suffocate trees standing in pond water as well as those standing in saturated soils making up beaver meadows that surround their ponds. Dead trees ultimately attract woodpeckers that hunt for insects in dead wood and end up whittling cavities for nesting birds. When beavers emerge on land, they harvest and dine on woody and non-woody vegetation while cutting stems and branches for dam construction and storing others in pond bottoms for winter rations. The flat-tailed brush hogs turn brushy wren habitats into territories that are safer for nesting prothonotaries.

When Homo sapiens builds dams to hold water for flood control and drinking water, we do what beavers do, but such man-made bodies of water are permanent, whereas beaver dams are temporary. After two or more decades, beaver wetlands succeed back into forests when beaver colonies relocate up or down streams to exploit new food resources. So, at Alum Creek, without beavers, I have to deal with House Wrens as I practice wildlife management for prothonotaries.

For now, I only have one more thing to try. In the past, I have faced nestjars with 1-3/8″ openings toward the lake to accommodate Tree Swallows while I point jars with 1-1/8″ entrances toward the forest to attract warblers. By making entrances easily visible to House Wrens, have I been inviting the brush-hopping-egg-stabbers to visit visible nest chambers where they cause mayhem with their sharp bills? One study found that wrens only need seven seconds per egg to stab and evict it. Is a visible cavity a stimulus for wrens to investigate? After all, while walking down the street, I stop to inspect shinny objects to see if I can be five or ten cents richer. Do I need the money? No, but it is in my nature to pick up lost coins. I think House Wrens have a similar compulsion when it comes to stabbing the eggs of other species. By preventing the hatching of hungry nestlings within their habitats, wrens guarantee more food for their own families.

So, for 2014, I plan to point all of my nestjars toward the lake, making it more difficult for House Wrens to see entrance holes from the forest edge. We will see…

Statistics from the AC-PROW Project – 2013:

Prothonotary Warblers (PROW)

• Thirteen nests were started with eggs.
• Once started with eggs, six nests(46.2%) fledged young.
• Of 51 eggs laid, 28(54.9%) hatched, and 26(51%) fledged. Of hatchlings, 92.9% fledged.
• An average of 4.33 fledglings per nest flew from six successful nests.
• From first egg through last fledging, the PROW nest season lasted 92 days from May 7 through August 9.
• Males built moss nests in 24(53.3%) of available nest chambers while females finished nests and laid eggs in 13 nests in 11(24.4%) chambers.
• Before 2013, July 5 used to be the record first-egg-date established by two PROW nests. Three nests in 2013 broke the July 5 record with first-egg-dates of July 11, 12 and 14, respectively.

Tree Swallows (TRES)

• Twenty-three nests started with eggs and 20(87%) fledged young.
• Of 120 eggs laid, 87(72.5%) hatched, and 84(70%) fledged. Of hatchlings, 96.6% fledged.
• The average fledged for 20 successful nests is 4.2 per nest.
• Two nestjars raised two successive broods.
• From first egg through last fledging, the TRES nest season lasted 86 days from May 6 through July 30.

House Wrens (HOWR)

• Wrens attempted eight nests with eggs and all were successful.
• Of 50 eggs laid, 46(92%) hatched, and 46(92%) fledged. All hatchlings grew to fledge.
• The average number of fledglings from each of eight nests is 5.75.
• Wrens occupied active nests from May 10 through July 27 for a 79-day nest season.