Effective nut dispersal by magpies (Pica pica L.) in a Mediterranean agroecosystem
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Scatter-hoarding animals such as corvids play a crucial role in the dispersal of nut-producing tree species. This interaction is well known for some corvids, but remains elusive for other species such as the magpie (Pica pica), an abundant corvid in agroecosystems and open landscapes of the Palearctic region. In addition, the establishment of the individual dispersed seeds—a prerequisite for determining seed-dispersal effectiveness—has never before been documented for the interaction between corvids and nut-producing trees. We analyzed walnut dispersal by magpies in an agroecosystem in southern Spain. We used several complementary approaches, including video recording nut removal from feeders, measuring dispersal distance using radio tracking (with radio transmitters placed inside nuts), and monitoring the fate of dispersed nuts to the time of seedling emergence. Magpies were shown to be highly active nut dispersers. The dispersal distance averaged 39.6 ± 4.5 m and ranged from 4.1 to 158.5 m. Some 90% of the removed walnuts were cached later, and most of these (98%) were buried in the soil or hidden under plant material. By the time of seedling emergence, ca. 33% of nuts remained at the caching location. Finally, 12% of the cached nuts germinated and 4% yielded an emerged seedling, facilitating the transition to the next regeneration stage. The results demonstrate for the first time that magpies can be an effective scatter-hoarding disperser of a nut-producing tree species, suggesting that this bird species may play a key role in the regeneration and expansion of broadleaf forests in Eurasia.
KeywordsCorvidae Forest regeneration Juglans Radio tracking Scatter-hoarding Seed caching Seed dispersal effectiveness
This study was supported by the projects CGL2014-53308-P of the Spanish Government and Remedinal 3 (S2013/MAE-2719) of the Madrid Government. The Consejería de Medio Ambiente (Junta de Andalucía) provided fieldwork permission. LMB was supported by a FPI scholarship (BES-2015-075276) from the Spanish Government. AL acknowledges support from the University of Granada and Project GEI Spain (CGL2014-52838-C2-1-R) funded by the Spanish Ministerio de Economía y Competitividad, including European Union ERDF funds. We thank Dr. E.W. Schupp and two anonymous reviewers for providing suggestions that enhanced the manuscript.
Author contribution statement
JC, LPC, PVS, SR, and JMRB conceived and designed the experiments. JC, MMM, AL, and LMB performed the field work. JC, MMM, and AL performed statistical analyses. JC wrote the first draft of the manuscript; all authors provided editorial advice.
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