The Defamated Magpie

The common magpie belongs to the family -corvidae- (commonly known as corvids) and includes well-known species such as the common crow, the common crow, the western jackdaw or the Eurasian jay. In this family there are the largest species of passerines. It is a bird with a palearctic distribution and unmistakable appearance that is very abundant in our country. It is medium in size (40-50 cm in length with tail included), black and white in color and has no notable differences between males and females (without sexual dimorphism).

It also has an iridescent plumage that gives it a metallic sheen in green lines (tail feathers) and blue in secondary feathers.

La Iridescence It is an optical phenomenon by which the color of a surface varies depending on the angle at which the light hits. It is also a phenomenon that plays a fundamental role in the communication of numerous species of fauna around the world (Stuart-Fox et al., 2021).

In the case of the defamed magpie, recent studies (Nam, Lee, Lee, Choi, & Choe, 2016) have evaluated the role of the coloration of this species, pointing out that there are significant differences (subtle to the human eye) in the color scale between age groups. Adult birds are those that have a more vivid and saturated color than juveniles. In addition, they observed that more vivid tones in the tail corresponded to adult birds, especially males. These differences appear to be a visual signal indicative of the individual's quality.

As we have already mentioned, the phenomenon of iridescence goes beyond the aspects discussed at the species level and, in the case of corvids, it plays a fundamental role in multiple species of this family. Corvids have an omnivorous diet, varying depending on the species and time of year. These birds have a great capacity for adaptation, which has contributed to their cosmopolitan distribution. They are also optional scavenging species, which means that, even if dead animals do not constitute the basis of their diet (strict scavenging), they can, on an occasional basis, incorporate this strategy as a form of food.

Most of the time, when a magpie or other corvid finds a corpse, they start by ingesting the soft parts, but soon find that they have no ability to access the animal's hard parts. It is at this time that, grouped into gangs that make continuous movements in their struggle to obtain more food from the corpse, they manage - aided by the iridescence of their plumage - to attract the attention of larger scavenging species. Generally, it is griffon vultures (sometimes accompanied by a black vulture) who, on their long daily trips gliding across the sky, detect the signal and descend quickly. Once they reach the corpse, the banquet begins.

Griffon vultures have a powerful beak capable of easily piercing the skin and their long, muscular neck, devoid of feathers, is capable of penetrating through any hole. During the time that vultures feed, the corvids stay nearby trying to keep track of small pieces of meat that may become available. After several hours, griffon vultures usually retire and that's when smaller species (milanos, alligators, foxes, corvids, etc.) fight for the remaining food. This interaction, where multiple species benefit, is called mutualism. However, the food web established around a carrion can be very complex, even benefiting other species of passerines (not just corvids) that opportunistically exploit this resource (Moreno-Opo & Margalida, 2013). For all these reasons, necrophagous bird species are essential for the maintenance of ecosystems thanks to their work of removing corpses from the natural environment.

Vultures and corvids have been heavily stigmatized in popular culture: ominous birds associated with dark and shameless premonitions about death. The common magpie is also a species that has always been persecuted by rural people, who saw it as a threat due to its bad reputation as a predator of other birds' eggs. The defamed magpie... However, this vision is changing thanks to the increase in knowledge about its trophic ecology, which is allowing us to obtain a much broader and more complex view of the role of this species in the ecosystem.

Finally, mention should be made of the role of the magpie as a bird that disperses large seeds. First of all, we should start by explaining what exactly this function consists of. The “scatter-hoarding animals” or “hoarder-disperser animals” are those that keep food to cover the energy needs of periods of scarcity. There is a well-known phenomenon that occurs mainly among tree species of the genus Quercus (oaks, thickets, oaks, etc.) and bird species from the corvid family.

Jays, for example, are considered one of the typical dispersing species of acorns in the Mediterranean forest. In the periods when the fruits are available, the jay is dedicated to collecting them and hiding them in different places in their territory to use them in winter if necessary.

However, many of these seeds are not recovered for various reasons (oblivion, death of the individual, lack of need, etc.) and in these cases, those that have the right conditions for germination can give rise to new seedlings. In the case of jays, it has been estimated that a single individual is capable of dispersing between 1000 and 5000 acorns in a year, depending on the species and age group (Kurek, Dobrowolska, Wiatrowska, & Dylewski, 2018).

Recently, several studies have demonstrated that the magpie could play a similar role in the dispersion of nuts (Castro et al., 2017) and acorns (Martínez-Baroja et al., 2019), with dispersion rates of up to 1372 acorns per season and individual (Martínez-Baroja et al., 2019). In addition, it could perform an ecosystem function complementary to jays (birds with forest habits), inhabiting more open and fragmented agricultural landscapes where the phenomenon of natural regeneration is more limited.

References consulted:

Castro, J., Molina-Morales, M., Leverkus, A.B., Martinez-Baroja, L., Pérez-Camacho, L., Villar-Salvador, P.,... Rey-Benayas, J.M. (2017). Effective nut dispersal by magpies (Pica pica L.) in a Mediterranean agroecosystem. Ocology, 184 (1), 183—192. https://doi.org/10.1007/s00442-017-3848-x

Kurek, P., Dobrowolska, D., Wiatrowska, B., & Dylewski, Ł. (2018). What if Eurasian Jay Garrulus Glandarius would larder acorns instead of scatter them? iForest, 11 (5), 685—689. https://doi.org/10.3832/ifor2793-011

Martínez-Baroja, L., Pérez-Camacho, L., Villar-Salvador, P., Rebollo, S., Quiles, P., Gómez-Sanchez, D.,... Rey-Benayas, J.M. (2019). Massive and effective acorn dispersal into agroforestry systems by an overlooked. Ecosphere, 20 (12).

Moreno-Opo, R., & Margalida, A. (2013). Carcasses provide resources not exclusively to scavengers: Patterns of carrion exploitation by passerine birds. Ecosphere, 4 (8), 1—15. https://doi.org/10.1890/ES13-00108.1

Nam, H.Y., Lee, S.I., Lee, J., Choi, C.Y., & Choe, J.C. (2016). Multiple Structural Colors of the Plumage Reflect Age, Sex, and Territory Ownership in the Eurasian Magpie Pica pica. Acta Ornithologica, 51 (1), 83—92. https://doi.org/10.3161/00016454AO2016.51.1.007

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. Condor, 118 (2), 215—237. https://doi.org/10.1650/CONDOR-15-125.1

Stuart-Fox, D., Ospina-Rozo, L., Ng, L., & Franklin, A.M. (2021). The Paradox of Iridescent Signals. Trends in Ecology and Evolution, 36 (3), 187—195. https://doi.org/10.1016/j.tree.2020.10.009