Gardeners, ecosystem engineers and landscapers: fruit-eating birds are playing a fundamental role in protecting biodiversity and recovering vegetation in habitats affected by external disturbances, such as fires, storms, floods or strong winds.
Bird-mediated restoration in the Mediterranean is based on the role of trees as perches for fruit-eating birds, mainly in woody cultivation areas such as olive groves, almond or vineyards. These areas are more prone to germination and survival thanks to the birdlife that settles around the tree, speeding up colonisation and restoration of the ecosystem due to the dispersal of seeds.
Several scientific studies also highlight the remarkable role of birds in restoring forest areas by moving fruit seeds from areas undisturbed by fire to areas devastated by these catastrophes. The birds roost on the remaining burnt trees and shrubs and begin their function as seed dispersers.
Damaged or dead forest mass acts as an important structural component to attract birds to perform their role in bringing back life to the forest. The example of the jay (Garrulus glandarius), a member of the scatter-hoarding crow family, is a paradigmatic case in Europe and especially in oak and holm oak forests of the Mediterranean region (mainly Quercus robur, Quercus petraea and Quercus ilex).
The jay, which usually feeds mainly on insects, replaces its usual diet in autumn and winter when invertebrates are scarce. It is during these seasons that it exercises its function as a sower, and increases the harvest and consumption, primarily of acorns, but also of hazelnuts, chestnuts or any other type of fruit.
Jays choose the healthiest acorns, richest in nutritional properties that make them more suitable for germination, and systematically hides them in holes in trees, rocks or simply buries them in the ground. Each individual can hide many thousands of acorns in the forest, which becomes a crucial element for the repopulation of many forest areas. In the case of landscapes affected by fires, these birds use the dead trees and forest floors as hiding places to store acorns.
This close alliance between trees and birds is recognised as bird-plant mutualism. While the trees offer the birds food, protection and a place to build their nests, the birds return the favour by contributing to trees’ reproduction and dispersion, even predating on tree-harming insects.
Bird-mediated restoration processes are an example of this mutualism, where the bird gradually reinstates a habitat that will serve as a source of food and a refuge to hide from future predators. However, this natural process, which contributes to recovering the ecosystem and lost biodiversity, is at risk from the global decline of animal populations, in this case seed dispersers, due to climate change and human activities that affect the conservation status of species.
Sources & additional information:
- Cavallero, L., Raffaele, E., & Aizen, M. A. 2013. Birds as mediators of passive restoration during early post-fire recovery. Biological Conservation, 158, 342-350.
- Vallejo, R., Aronson, J., Pausas, J. G., & Cortina, J. 2006. Restoration of Mediterranean woodlands. Restoration ecology: The new frontier, 193-207.
- Pesendorfer, M. B., Sillett, T. S., Koenig, W. D., & Morrison, S. A. 2016. Scatter-hoarding corvids as seed dispersers for oaks and pines: a review of a widely distributed mutualism and its utility to habitat restoration. The Condor: Ornithological Applications, 118(2), 215-237.
