Scatter-hoarder birds can play a key role in the dispersal and recruitment of forest tree species through caching seeds, but accurate evaluation of their importance in this respect would require detailed monitoring of post-dispersal seed fate. To quantify seed fate under wild conditions researchers often use visual marks to locate the seed caches. However, the effect that these marks may have on scatter-hoarder birds, and hence on the estimation of post-dispersal seed fate, has so far been neglected. In this study, we experimentally analyse whether different visual marks used to locate caching sites may affect the removal rate of cached seeds by a scatter-hoarder corvid, the Eurasian Magpie Pica pica. We used three different procedures (treatments) to mark the caches: a small wooden stake placed at 50cm from the cache, a large wooden stake placed at the same distance, and no stake (no visual mark). Dispersal of walnuts placed in feeders was monitored with radio-tracking, and assigning the dispersed nuts to each procedure followed a stratified process that allowed us to create similar conditions across treatments. We found that mark type did not affect the recovery rate of cached nuts, which validates the results of the recovery rate in previous studies of this system. Marking cached nuts with wooden stakes up to 20cm above ground as done in this study seems therefore to be an appropriate way to assist researchers to locate sampling points when studying nut dispersal by magpies.
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