Eurasian Reed Warbler Migration Paper Critique

Regarding the Emlen funnel tests, 40.9% were discarded for being either inactive (7.4%) or disoriented (33.5%). There is no further information about which birds had their tests discarded, which could be an interesting fact to consider because it could change sample sizes and induce bias. In order to support the discarding of such tests, the researchers could refer to the variables that may have influenced the results, such as the weather or the age of the bird. It is possible that some of the discarded results belonged to juvenile birds on their first migration, which would use vector navigation since they still lack part of the map component of navigation that is gained through experience. Since birds may rely on multiple cues for navigation, this study does not provide the whole picture of bird migration because it was performed at fixed locations. An interesting follow-up study could track the same birds with satellite tagging to determine if they reached their breeding grounds despite having a sectioned V-1.