Species: Picoides dorsalis - American three-toed woodpecker
Distribution within R2
The American three-toed woodpecker (ATTW) is known to occur on all of the National Forest units in Region 2, with the exception of the Nebraska National Forest. This species is found mostly in the spruce-fir forest type during endemic population levels and they are also found in recently burned and beetle infested spruce and lodgepole forest types. The core distribution in R2 is highly associated with the distribution of spruce-fir forests.
This species has a broad distribution that follows the distribution of spruce-fir forests in North America. The vast majority of the distribution occurs in the boreal forests of Canada.
Confidence in Rank High
This species has a high dispersal capability and has irruptive population increases in response to increasing food supplies. It is thought that localized population increases are due as much to aggregations of dispersing birds as well as due to increased reproductive ability of local birds.
Confidence in Rank High
1, 2, 12
Abundance in R2
The ATTW is commonly a low-density but well distributed species. This species density has been increasing as a result of the ongoing bark beetle epidemic. In Colorado densities have been steadily increasing in the spruce-fir type from 1998 to 2007 (3- page 116).
The same pattern has been observed on the Medicine Bow National Forest:
Year D LCL UCL %CV n
2005 10 3 29 69 6
2006 27 11 66 55 21
2007 37 16 84 50 30
D = estimated density (birds/km2); LCL and UCL = lower and upper 90% confidence limits on D.
Population densities are anticipated to return to endemic levels as the new infestations of bark beetle killed trees decline. This is likely what the data from the recent integrated bird monitoring design for forests in Region 2 demonstrates (5 – page 19). A population increase followed by a return to endemic levels is also predicted in Loose 2009.
Confidence in Rank High
3, 4, 5, 6
Population Trend in R2
The current cycle of ATTW population growth followed by the current apparent decline is in direct response to the current bark beetle epidemics in the spruce and lodgepole pine forest types.
The ATTW populations are anticipated to increase dramatically in beetle killed lodgepole pine stands followed by a dramatic decline as bark beetle populations collapse following the stand mortality. Populations will seek refugia in mature spruce-fir dominated forests and return to endemic levels. (Loose 2009).
The PIF species assessment database listed ATTW as a ‘3’ for population trend, indicating that the population trend was highly variable or unknown (7).
The current anticipated downward trend is mostly considered a return to endemic population levels.
ATTW habitat expanded from spruce into lodgepole during the pine beetle outbreak and as the active infestations subside in the pine type, this species is anticipated to have its habitat contract back to core habitat areas of spruce-fir. Endemic populations habitat would be largely tied to spruce forests following the bark beetles. There is no shortage of snags in R2 for the foreseeable future.
The listing of the Canada lynx and resulting plan amendments have resulted in increased management restrictions in the spruce-type which although targeted towards lynx, likely may benefit ATTW as well.Some active spruce-beetle outbreaks are occurring in Region 2 (Rio Grande).
ATTW foraging occurs in areas with live infested and dead trees where it feeds primarily on the boles and major branches of trees by peeling the bark to extract insects (e.g. bark beetles). Three-toed woodpeckers forage more in live green trees than in dead trees, compared with other members of the Picoides genus (Short 1974). In 1958 G. D. Amman found that woodpeckers on Rabbit Ears pass spent 81% of their foraging time on Englemann spruce. In 1969 Koplin found that NTWs spent approximately 80% of their time foraging on Englemann spruce trees. This foraging habit will benefit the species when spruce beetles infest live spruce. This species is heavily dependent upon snags and live trees with heartrot for nesting. NTW were also found to select lodgepole pine stands for nesting stands (Goggans et al. 1988, Lester 1980). Snags at least 12 inches in diameter and at least 15 feet tall are used to excavate nest cavities. Clutch sizes are usually four and may range from three to six.
This woodpecker is among the most specialized predator of bark beetles in the spruce and lodgepole forest. The NTW is an important predator of spruce beetles during periods of outbreaks (Bock and Bock 1974). Kroll (1980) found that scaling of bark from the trees by woodpeckers indirectly increases mortality of bark beetles due to environmental conditions as well as predation and parasitism by insects. Woodpecker densities are known to increase significantly as bark beetle populations change from endemic to epidemic levels. NTW populations have the most pronounced increases in density due to increases in bark beetle populations compared to other species of woodpeckers found in subalpine forests in Colorado (Koplin 1969). Koplin found that increases in densities in areas infested with bark beetles is most likely due to drift and aggregation and not increased recruitment.
Jennifer A. Blakesley. 2008. Population densities of avian Management Indicator Species on the Medicine Bow National Forest. Supplemental Report MMWB-USFS07-01. Rocky Mountain Bird Observatory, Brighton, CO. 8 pp.
Blakesley, J. A., D. C. Pavlacky, Jr., and D. J. Hanni. 2010. Monitoring the birds of the Southern Rockies/Colorado Plateau Bird Conservation Region (BCR 16), 2009 field season report. Tech. Rep. SC-RMR-USFS09-01. Rocky Mountain Bird Observatory, Brighton, CO, 40 pp. http://www.rmbo.org/dataentry/postingArticle/dataBox/BCR16_2009_report_final.pdf
Loose, S. 2009. Response of three-toed woodpecker to environmental conditions under a no-action alternative. [Online]. USDA Forest Service. Rocky Mountain Region. Available: http://fsweb.r2.fs.fed.us/rr/ecology/barkbeetles/three_toed_woodpecker.0.doc
Partners in Flight Species Assessment Database: http://www.rmbo.org/pif/pifdb.html