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Providing evidence to improve practice

Individual study: Black bear Ursus americanus supplemental feeding reduces conifer damage on the Olympic Peninsula, Washington State, USA

Published source details

Ziegltrum G. I. (2004) Efficacy of black bear supplemental feeding to reduce conifer damage in western Washington. The Journal of Wildlife Management, 68, 470-474


This study is summarised as evidence for the intervention(s) shown on the right. The icon shows which synopsis it is relevant to.

Provide supplementary feed to reduce tree damage Terrestrial Mammal Conservation

A replicated, randomized, paired sites, controlled, before-and-after study in 1999–2002 in 14 coniferous forest sites in Washington, USA (Ziegltrum 2004) found that supplementary feeding reduced tree damage caused by black bears Ursus americanus. The number of trees damaged by bears in sites where supplementary feeding was used was lower (3–10 trees/year) than in sites where no supplementary feeding was used (15–26 trees/year). When supplementary feeding was stopped at one site, the number of trees damaged by bears increased from 6 to 40/year. In March 1999, in fourteen 16–20-ha sites, bear-damaged trees were marked with paint. Sites with similar amounts of damage were paired. In April 1999, one site/pair was randomly chosen to have two plastic drums containing food pellets placed in it, while the other site had no supplementary food provided. Plastic drums were refilled weekly in April–July with 100 kg of pellets. In the first year, at sites where supplementary feed was provided, beaver Castor canadensis carcasses were hung from trees to attract bears. In July 2000, supplementary feeding was stopped at two of the seven sites (results not presented for the second site due to the feeding station not being maintained prior to this). Sites were surveyed for bear damage to trees in July of 1999–2002.

(Summarised by Phil Martin)