Conservation releases of captive-reared Grouse in Europe. What do we know and what do we need?

Black Grouse, Capercaillie and Hazel Grouse are endangered in several central and west European countries. To augment or re-establish local populations of these species, releases of captive-reared birds have been conducted in many places. Provisional results of some releases were encouraging, but to date, none of these projects is known to have established a viable population. Factors that might cause a release to succeed or fail are still poorly understood. By viewing release projects as individual case studies, the compilation and synthesis of results of several studies should allow quantitative evaluation and determination of those factors that are essential for successful releases.

We studied the feasibility of performing meta-analysis by reviewing published results of 29 documented release projects with Black Grouse. Capercaillie and Hazel Grouse, conducted between 1980 and 2000 in six European countries. In total, more than 5500 captive-reared birds were released within these projects.

Due to lack of comparable information in the published reports, only few factors could be included in statistical evaluation. Among those, the total and the yearly number of birds released and the number of release years were the only significant predictors for project success. The resulting models suggest that annual releases of at least 30 birds are needed for a period of more than 6 years, to reach a 50% probability for survival and reproduction of released birds.

Despite limitations in the data set, meta-analysis appeared to be a feasible tool for evaluation of grouse releases. To enhance future analyses, however, improved documentation of release projects is needed. We suggest a list of topics that authors should consider when reporting grouse release studies.