Massive and effective acorn dispersal into agroforestry systems by an 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 jays are absent, such as old fields far from acorn sources, oak recruitment still occurs. We hypothesize that the Eurasian 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 radio‐tagging 337 acorns, we quantified that (1) magpies cached 41–56% of the annual acorn production of Quercus ilex trees in single caches on the ground; (2) breeding pairs, and especially males, were the main acorn dispersers; (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 density of emerged seedlings (56–439 seedlings/ha). We evidence that magpie could be a key species in the regeneration of oak agroforestry mosaics because they massively and effectively dispersed acorns. However, in our 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 and oaks overlap widely in Eurasia, effective acorn dispersal by magpies could have a significant role in large‐scale oak forest recovery in strongly fragmented landscapes.

Caching territoriality and site preferences by a scatter‐hoarder drive the spatial pattern of seed dispersal and affect seedling emergence

“…Consistent with this finding, Martínez‐Baroja et al. (2019) determined that magpie breeding pairs removed 89% of the acorns from the feeders located within their territories, whereas the rest of removed acorns were taken by neighbouring breeding magpies or juveniles. These ‘thieves’ moved and cached the stolen acorns in their own caching territories in the second study period (2016–2017) (Figure ).…”

“…We monitored acorn removal by magpies with trail cameras (Moultrie MCG‐12634; Moultrie Products, Alabama, USA), which recorded 1‐min videos when movement was detected. Once the magpies got used to the feeders, we regularly supplied radio‐tagged and untagged acorns (Martínez‐Baroja et al., 2019; Pons & Pausas, 2007) from November 2015 to April 2016. Removed acorns were located on the same day to avoid post‐dispersal predation or secondary dispersal.…”

“…To address this goal, we used the interaction among Eurasian magpie ( Pica pica L.) and holm oak ( Quercus ilex L.) as our study system. Magpies are massive acorn scatter‐hoarders, that is, disperse large number of acorns (Martínez‐Baroja et al., 2019) and territorial breeders (Baeyens, 1981; Birkhead, 1991; Szala et al., 2020) that inhabit open landscapes. The holm oak is the most important tree in agroforestry systems in the western Mediterranean Basin (Pulido & Díaz, 2005).…”

Synzoochory: the ecological and evolutionary relevance of a dual interaction

“…In addition, Holm‐oak acorns are consumed by larder‐ and scatter‐hoarding rodents, such as black rat Rattus rattus , woodmouse Apodemus sylvaticus , Algerian mouse Mus spretus and red squirrel Sciurus vulgaris , which may disperse and cache some of the acorns they encounter (Bonal & Muñoz, ; Muñoz & Bonal, ; Pons & Pausas ; Gómez, Puerta‐Piñero & Schupp, ). Finally, acorns are consumed by scatter‐hoarding corvids, such as hooded crow Corvus cornix , Eurasian jay Garrulus glandarius and magpie Pica pica , which disperse and cache a large proportion of the acorns they harvest (Santos & Tellería, ; Gómez, ; Pulido & Díaz, ; Pons & Pausas, ; Melletti & Mirabile, ; Morán‐López, Alonso & Díaz, ; Martínez‐Baroja et al ., ). Thus, the animals consuming Holm‐oak acorns occupy different positions on the continuum running between full antagonism and full mutualism, and in fact together occupy much of the gradient (Fig.…”

The influence of fencing on seedling establishment during reforestation of oak stands: a comparison of artificial and natural regeneration techniques including costs

“…Scatter-hoarding birds and rodents may consume large quantities of acorns but some will survive and germinate in suitable places (Gómez et al 2019). Birds in particular can carry acorns far from seedbearing trees to open areas where they may develop successfully (Pesendorfer et al 2016;Martínez-Baroja et al 2019).…”