Massive and effective acorn dispersal into agroforestry systems byan overlooked vector, the Eurasian magpie (Pica pica)

Abstract

Oak regeneration and the expansion of forested sites in Eurasia rely on acorn dispersal by animals,especially the Eurasian jay (Garrulus glandarius). However, in open agroforestry systems where jaysare absent, such as old fields far from acorn sources, oak recruitment still occurs. We hypothesize that theEurasian magpie (Pica pica), an abundant corvid in this system, substitutes the jay in its seed dispersal function.By ringing 169 magpies, video recording >7500 acorn removal events with trail cameras, and radiotagging337 acorns, we quantified that (1) magpies cached 41&#-56% of the annual acorn production of Quercusilex trees in single caches on the ground; (2) breeding pairs, and especially males, were the main acorndispersers; (3) each breeding magpie cached 169&#-1372 acorns in 6 weeks; and (4) the effectiveness of dispersal(percentage of cached acorns resulting in seedlings) was 0.6&-2.4%, which (5) yielded a high densityof emerged seedlings (56&-439 seedlings/ha). We evidence that magpie could be a key species in the regenerationof oak agroforestry mosaics because they massively and effectively dispersed acorns. However, inour particular study site, effectiveness was low probably due to herbivory and summer drought stress (i.e.,a context limitation rather than an intrinsic limitation of the disperser). As the distributions of magpies andoaks overlap widely in Eurasia, effective acorn dispersal by magpies could have a significant role in largescaleoak forest recovery in strongly fragmented landscapes.