The CHJV is assessing the effects of savanna-woodland restorations on 14 priority bird species, including Worm-eating Warblers. Photo by Lloyd Spitalnik. Copyright 2007.

Winter 2008

The Central Hardwoods Joint Venture is using the principles of Coordinated Bird Monitoring to estimate the population size and distribution of Cerulean Warblers and assess the effects of savanna-woodland restorations on priority bird populations in the Central Hardwoods Bird Conservation Region. The first field season for both projects was completed in 2007.

"The idea behind Coordinated Bird Monitoring is for Joint Ventures to determine what their data needs are," said Jane Fitzgerald, coordinator of the CHJV. "Then, with a good sampling design and sampling protocol, they work on a problem at an appropriate scale, whether that means the entire Bird Conservation Region (BCR) or some sub-section of the BCR, and involve the partners in the actual sampling and data collection."

The need for the Cerulean Warbler assessment was clear.

"This species has declined in abundance by 75 percent over the course of the last 40 years," said David Pashley, Vice President for Conservation for the American Bird Conservancy. Pashley represents the Conservancy on the CHJV board. "One of the problems is that the causes of the decline are unknown."

Likewise, several efforts to restore savanna-woodland habitats have taken place in the Central Hardwoods BCR, but no evaluations had been done to show how priority bird species were responding to the projects.

With the data needs well understood, the CHJV contracted with Frank Thompson of the US Forest Service's Northern Research Station in Columbia, Missouri, to design an appropriate sampling design and protocol.

"Any time you conduct a bird survey, you invariably do not count all the birds that are present because you fail to detect some. For instance, they might not sing while you are there," Thompson said. "These methods estimate the probability a bird is detected, so in essence, you can correct your estimate."

To estimate the probability of detecting a bird, Thompson incorporated both time to detection and distance from the observer into the sampling protocol. The two methods will be compared in terms of their ease of use in the field and their accuracy.

To further strengthen the sampling design, sample sites were selected randomly from within the ecoregions of interest.

"More often than not, biologists use a sample of convenience. That is, they select points that may be easier to get to, and hence more efficient, to sample," Thompson said. "By using a true random sample we'll get a more representative estimate."

Once the two studies were designed, partner organizations provided personnel for the fieldwork. For the Cerulean Warbler assessment, thirteen observers from Arkansas, Illinois, Kentucky, Missouri and Tennessee conducted bird counts at 1,689 points from late May to the end of June 2007, covering more than 67,000 hectares across the five states. For the assessment of savanna-woodland restorations, partners in three states - Arkansas, Missouri and Tennessee - conducted point-count surveys for 14 bird species at each of ten managed and ten control sites. At each site, several point counts were conducted along a transect, for a total of 237 point locations.

Preliminary results from the 2007 field season indicate that using both distance and time data provides the best estimate of species abundance, but also makes for an overwhelming field protocol. A second field season is planned for 2008.

Taken together, the assessments will guide biologists in designing accurate bird surveys while also evaluating the status of Cerulean Warblers and the effectiveness of savanna-woodland restorations for priority bird management.

More on the Cerulean Warbler Assessment
More on the Savanna-Woodland Restoration Assessment

Point counts done in restored savannas and woodlands, such as this one in Arkansas, will be compared to counts in non-restored areas to assess the impact of restorations on priority bird species. Photo by Steve Duzan, Ozark-St. Francis National Forest.