Interpreting variation in bird migration times as observed by volunteers

As a result of changes in climate over the past 100 years, many birds are arriving at points along their migration routes earlier in the spring now than they did in the past, Increasingly, researchers are relying oil a variety of data Sources, Such as naturalist journals and bird-club records, to document migration times. However, it is not clear whether researchers can successfully use different sources of data to compare changes in migration times. We examined 25 years of changes in migration times for 30 species of birds at Mt. Auburn Cemetery in Cambridge, Massachusetts, as documented by bird-club members and published in a regional bird journal. We found that, overall, birds arrived, earlier in warmer springs in eastern Massachusetts. We compared our findings With those of previous studies in Massachusetts, which included data from a standardized bird-banding station and observations from a naturalist's journal and bird-club records. On a species-by-species basis, changes in migration times were not correlated among the Studies. We believe that local changes in Population sizes and sampling effort at some of the sites may have contributed to the lack of correlation. For the Purpose of comparing changes in migration time,,, across species and locations, standardized bird-banding data are preferable to data collected by volunteer naturalists. However, naturalist data sources are useful and reflect the widely observed trend toward earlier migrations in warm springs.