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Endangered Bird Sees Increase

Arkansas Natural Heritage Commission - Friday, June 18, 2010

Pine City Natural Area (NA), located in Monroe County in eastern Arkansas, supports the only known population of federally endangered red-cockaded woodpeckers (Picoides borealis, RCW) throughout the Mississippi Alluvial Plain. ANHC staff monitors the population regularly and manages the natural area for this rare bird’s habitat.

In April 2010, monitoring revealed that this natural area was, for the first time, supporting three pairs of RCWs. One of the new pairs resulted from a little matchmaking with a young female from the Ouachita National Forest (ONF). The female was translocated to Pine City NA in early March this year. She was placed with a single male, born at Pine City NA in 2009, who had established a new territory last summer in a portion of the natural area where habitat restoration had just been completed. Unexpectedly, this female left the male she was paired with and displaced one of the other breeding females just as nesting season kicked into high gear.Fortunately, she was tending to two nestlings in early June, which could provide a beneficial boost to the gene pool of this small population. In addition, the other pair successfully fledged three nestlings in late May and the single male continues to defend his territory and will likely remain there until paired at a later date.

RCWs are cooperative breeders, and the term “group” is more informative with these birds as opposed to “pair.” A typical RCW group consists of a breeding pair and one helper, though some groups have more helpers and some have none. The helpers assist in raising young, including incubation, brooding, and feeding. Cooperative breeding systems, which occur in about 3% of bird species worldwide, appear to evolve when there is a scarcity of some resource in their environment that limits the opportunities of younger birds to breed. In the case of the RCW, that limiting factor is available cavities for roosting and nesting. RCWs excavate their cavities in live pine trees which typically takes several months or even years to complete. Because of the length of time involved in creating new cavities, young male RCWs are reluctant to start new territories and tend to stay in their natal territory and wait for it or a nearby territory to become available. Young females tend to disperse from their natal territory in search of RCW groups lacking a female. Single males defending a territory with completed cavities are tracked as single bird groups because they often remain in that territory until paired and eventually contribute to producing offspring and helping maintain or increase population size.

Management for RCWs requires patience and persistence, and there will be opportunities in the coming year to reach or exceed the goal we set for 2010. The single male may end up paired through the natural dispersal of birds born this year at Pine City NA. If not, we will conduct a reciprocal translocation with the ONF to pair the single male again (this will aid their population as well). Success rates of the swaps are around 50% so this single male has a good chance of starting a family.

Because RCWs are cooperative breeders, population measures for the species include tracking “average group size.” The average group size of adults at Pine City NA (about 3) is currently very good and just a little above that observed across the species range. This is important because helpers at the nest typically result in greater numbers of nestlings fledged and higher fledgling survival rate. In addition, helpers provide a pool from which to draw replacement breeders, which aids in stabilizing the number of breeding groups, the key population parameter. The average group size at Pine City NA could be maintained or even increase slightly if the nest season continues to be as successful as it has been thus far.

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