Parrots are flashy species arousing the interest of many people due to the variety of their colours or their wide range of sounds. However, the role of these animals in the interaction with the plants that they eat have been just recently started to study, showing that, in addition to benefit from the plants eating them, they can also offer unexpected mechanisms to help disperse their seeds.

Zoochory is a mechanism by which animals become seed dispersal agents. It is a mutualistic relationship, that is, a relationship in which different species benefit from each other. These phenomena play a fundamental role in the composition of biodiversity, but due to their great complexity, much is still unknown about it. Among the different mechanisms of zoochory, epizoochory, seed dispersal by adhesion to animals, is one of the least studied and its ecological implications are hardly known.

In order to clarify the real role of epizoochory in frugivorous birds, the Doñana Biological Station, together with other institutions, has carried out an eight-year study on the potential ecological implications of this phenomenon in parrots (Order Psittaciformes), a large group of frugivores considered primarily seed predators and whose role in mutualistic relationships has been recognized just in recent years.

Citizen science to increase the number of species studied

The team carried out different works in 17 countries on five continents from 2012 to 2020, aiming to record any epizoochory event between parrots and the plants they eat and to measure dispersal distances. In a complementary way, and with the help of citizen science, they did a search in Internet photo galleries (eBirds, WikiAves, etc) showing epizoochory events. "The attraction that parrots arouse in people makes their photos be very abundant on the web, increasing the chances of finding more evidence," says Dailos Hernández Brito, researcher at the Doñana Biological Station (EBD-CSIC) and first author of the study.

In total, the team recorded about 2000 observations of epizoochory events (9.5% from images from Internet portals) obtained in 48 countries, involving 116 parrot species and at least 96 different species of plants. "Despite the large number of cases, we became aware of this phenomenon very late, after reviewing our photos from the first campaigns," explains researcher José Luis Tella from the EBD-CSIC. "Many cases will surely have been overlooked due to the difficulty of seeing the small seeds attached to the parrots, well camouflaged by vegetation."

Nearly half of the parrot species with more than one plant species. In addition, depending on the geographical origin of the participating species (native or exotic), the dispersions were highly polarized; the non-native parrots dispersed more exotic plants (80%) while the native species of parrots dispersed more native plants (91%).

 Seeds did not show conventional mechanisms for epizoochory

In most instances, tiny seeds were attached to the beak or head feathers of individuals when they were feeding on the pulp of fleshy fruits (e.g., family Moraceae). In the rest of the cases, seeds came from dry dehiscent fruits (e.g., capsules and legumes) that were also attached to the facial feathers and the beak through resins and mucilages in seeds. Interestingly, some seeds with specialized structures to be dispersed through the wind (anemochory), such family Malvaceae and Salicaceae, easily adhere on their body surfaces.

These epizoochory events do not conform to a standard of accidental seed dispersal by animals, but rather a type of mutualistic interaction not previously considered. The plants eaten by parrots do not have seeds with conventional structures for epizoochory, like hooks, but they do have other dispersal mechanisms, such as anemochory, seed dispersal through the wind or endozoochory, through the animals themselves by swallowing seeds.

The dispersal distances ranged from 12 to 452 meters, with an average of 118.5 meters. parrots usually dropped seeds that were detached from their body surface in grooming sessions with the beak or by rubbing them against tree branches, as well as during conspecific interactions such as social grooming, courtship feeding, and parental care. "These data are promising. Going in depth in the efficiency of this dispersal mechanism can offer us future lines of research, since we hope that this phenomenon will not only occur in parrots, but also in other frugivores", points out Dailos Hernández Brito.

The study encompasses a wide range of biomes and species, so the ecological and conservation implications materialize on a global scale. "In recent years, our team has been demonstrating the mutualistic role that parrots play as seed dispersers. With this study, we add a new mechanism that is crucial for the functioning and structuring of communities and ecosystems", concludes José Luis Tella. The threats looming over a third part of the existing parrot species, such as the loss of habitat and the wildlife trade, can lead to the loss of ecological functions in these complex relationships or its alteration in biological invasions. Therefore, the study and understanding of these biological interactions can facilitate the proper development of conservation plans in this scenario of global change.

Reference

Dailos Hernández-Brito, Pedro Romero-Vidal, Fernando Hiraldo, Guillermo Blanco, José A. Díaz-Luque, Jomar M. Barbosa, Craig T. Symes, Thomas H. White, Erica C. Pacífico, Esther Sebastián-González, Martina Carrete, José L. Tella. Epizoochory in Parrots as an Overlooked Yet Widespread Plant-Animal Mutualism. Plants 2021, 10(4),  760; https://doi.org/10.3390/plants10040760