Does fire affect Eastern Bluebird nest success at Shaw Nature Reserve?

Joseph Smith is a rising senior at Lake Superior State University. This summer, he studied the effect of prescribed fire on Eastern Bluebird nesting success at Shaw Nature Reserve as part of  MBG’s NSF-funded Research Experience for Undergraduates (REU) program.

Among the rich plant diversity at Shaw Nature Reserve are a wide range of animal species, including the Eastern Bluebird (Sialia sialis). The Nature Reserve is home to an extensive bluebird trail consisting of 86 nest boxes in the north-central region of the reserve. This summer, I have been working with Dr. Leighton Reid and a citizen scientist, Lynn Buchanan, in an effort to understand the effects that land management practices have on bluebird nest success.

Prescribed fire is one of the most important management practices used at Shaw Nature Reserve. In the 2016-2017 burn season, for instance, nature reserve staff set fire to 306 ha (756 acres) of woodlands, prairies, and glades to restore and maintain open vegetation structure and a high diversity of native plants. However, it was unclear what effect these fires might have bluebirds.

FireHypotheses

Hypothetical effects of prescribed fire on Eastern Bluebird nest success. +/- symbols denote the short-term effect of fire on snakes and arthropods, and the effect of snakes and arthropods on bluebird nest success. Photo credits: (1) Black rat snake (Pantherophis obsoletus) by John Mizel CC BY-NC-SA 2.0, (2) Bluebird eggs by Bailey & Clark (2014); (3) Red-legged grasshopper (Melanoplus femurrubrum) by Gilles Gonthier; (4) Prescribed fire courtesy of Shaw Nature Reserve.

We hypothesized that fire might affect bluebird nesting success in two ways. First, fire could reduce the food supply for nesting birds. When understory vegetation burns, many arthropods are also killed, and it takes some time for their populations to rebound. During the lag, bluebirds might have less to eat, which could result in poorer nest success.

Second, fires could increase nest success by reducing the risk of snake predation. Bluebird boxes at Shaw Nature Reserve are equipped with baffles to prevent snakes from getting in, but snake predation still occurs sometimes. After a fire, there is less vegetation to hide snakes from their own predators, like raptors, and we surmised that fewer snakes could mean more successful bluebird nests.

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The Bluebird Trail at Shaw Nature Reserve. Bluebird nest boxes are shown in yellow.

We tested our hypotheses using a long-term dataset collected by volunteers. Over the past eight years, Lynn Buchanan and her team have monitored the nest boxes on the bluebird trail and kept records of their observations. Each week during the breeding season, they peek into all of the boxes and record the number of eggs and nestlings, how many nestlings fledged, and whether or not the nest was predated.

With statistical help from Washington University researcher Joe LaManna, we found that prescribed fire had little or no effect on bluebird nesting. We compared areas that were burned with areas that were mowed, and we also compared burned areas at different time intervals since the most recent fire (0-3 years). Likewise, we found no effect of prescribed fire on the rate of snake predation.

Species Probability of nest success (%)* Probability of snake predation (%)* Did nest success change from 2009-2016? Did prescribed fire have an effect on nest success?
Eastern Bluebird 90.8 ± 0.5 4.6 ± 0.3 No No
House Wren 92.1 ± 0.1 4.0 ± 0.3 No No
Tree Swallow 92.1 ± 0.1 4.8 ± 0.4 No No

*Standard errors are shown

While the lack of significant results can be slightly disheartening after an entire summer of work, it is reassuring that the bluebird population is thriving at Shaw Nature Reserve. Overall, we calculated that 90.8 ± 0.5% of bluebird nests produced at least one fledgling. In addition, two other species (House Wrens and Tree Swallows) that commonly use bluebird boxes also had high nest success.

There are more aspects of bluebird nesting to look at. For instance, the time from when an egg hatches until the chick leaves the nest could be longer in recently burned areas if there is less food (i.e., arthropods) available. In the meantime it appears the bluebirds are living well at Shaw Nature Reserve.

BluebirdAndBox

Eastern Bluebird (left) and bluebird nest box (right) at Shaw Nature Reserve. Photo credits: (L) Bluebird by Andy Reago & Chrissy Mclarren; (R) bluebird nest box by Rachel Weller.

Monitoring Breeding Birds at Shaw Nature Reserve

The best time to start a long-term dataset is 25 years ago. The second-best time is now!

Summer solstice is the height of the bird breeding season at Shaw Nature Reserve. Dozens of species are singing, from Dickcissels in the open prairies, to Prothonotary Warblers in the damp forests along the Meramec River, to near-ubiquitous Blue-gray Gnatcatchers, seemingly everywhere.

 

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For six days this month, two students and I are counting birds systematically across Shaw Nature Reserve to learn how they are influenced by ecological restoration. Birds are a common focus for monitoring restoration projects because they can be observed efficiently over large areas, and because they often respond quickly to changes in ecosystem structure. Ovenbirds, for instance, prefer the dark shade of closed-canopy forests, whereas Kentucky Warblers replace them in woodlands that have been burned (fire is a common restoration strategy in many Missouri ecosystems).

Map

Locations of bird counting stations at Shaw Nature Reserve. Each point is at least 100 meters from the edge of a management unit and at least 200 meters from any other station.

A typical bird survey goes like this:

  • 4:20 AM. I pour a travel mug of coffee, pick up a student to help record data, and drive to Shaw Nature Reserve in the dark. There are way too many deer along the side of I-44.
  • ~5:00 AM. We arrive at Shaw Nature Reserve in twilight and hear a cacophony of birds singing over one another. Indigo Buntings scatter from the loop road ahead of our car.
  • ~5:15 AM. We arrive at the first bird counting station and record the temperature, cloud cover, and wind speed. For five minutes, we write down each bird that we hear or see. Sometimes during these early morning counts, nocturnal birds, like Chuck-will’s-widow, are still calling.
  • ~5:30-10:00 AM. After we finish a point, I set my GPS to navigate to the next point on our route and we continue to record birds until mid-morning, by which time it is warm and many birds have stopped singing (although the Red-eyed Vireos are still going strong).
Combo

Leighton Reid (left) listens to Wood Thrushes and Northern Parulas while REU student Joseph Smith (Lake Superior State University, right) records data. As indicated by the abundant bush honeysuckle (Lonicera maackii; e.g., by Leighton’s right leg), this particular part of the reserve has yet to be restored.

This is our inaugural bird survey at Shaw Nature Reserve. Unlike many of my projects, this one does not have explicit apriori hypotheses; I’m not trying to “test” anything. Instead, I intend for these data to be used for monitoring and demonstrating progress. Over time, I hope and expect these observations to provide a record of biodiversity change as portions of the reserve are restored and managed.

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Counting Common Yellowthroats, Dickcissels, and Red-winged Blackbirds at dawn at the Wetland Mitigation Bank.

For more information on breeding birds at Shaw Nature Reserve, you can explore citizen science observations on eBird, including this printable checklist of birds recorded in June during the past 10 years.