Mutually enhancing organisms can become reciprocal determinants of their distribution, abundance, and demography and thus influence ecosystem structure and dynamics. In addition to the prevailing view of parrots (Psittaciformes) as plant antagonists, we assessed whether they can act as plant mutualists in the dry tropical forest of the Bolivian inter‐Andean valleys, an ecosystem particularly poor in vertebrate frugivores other than parrots (nine species). We hypothesised that if interactions between parrots and their food plants evolved as primarily or facultatively mutualistic, selection should have acted to maximize the strength of their interactions by increasing the amount and variety of resources and services involved in particular pairwise and community–wide interaction contexts. Food plants showed different growth habits across a wide phylogenetic spectrum, implying that parrots behave as super‐generalists exploiting resources differing in phenology, type, biomass, and rewards from a high diversity of plants (113 species from 38 families). Through their feeding activities, parrots provided multiple services acting as genetic linkers, seed facilitators for secondary dispersers, and plant protectors, and therefore can be considered key mutualists with a pervasive impact on plant assemblages. The number of complementary and redundant mutualistic functions provided by parrots to each plant species was positively related to the number of different kinds of food extracted from them. These mutually enhancing interactions were reflected in species‐level properties (e.g., biomass or dominance) of both partners, as a likely consequence of the temporal convergence of eco‐(co)evolutionary dynamics shaping the ongoing structure and organization of the ecosystem. A full assessment of the, thus far largely overlooked, parrot–plant mutualisms and other ecological linkages could change the current perception of the role of parrots in the structure, organization, and functioning of ecosystems.

Seed dispersal is one of the most studied plant–animal mutualisms. It has been proposed that the dispersal of many large-seeded plants from Neotropical forests was primarily conducted by extinct megafauna, and currently by livestock. Parrots can transport large fruits using their beaks, but have been overlooked as seed dispersers. We demonstrate that three macaws (Ara ararauna, A. glaucogularis and A. severus) are the main dispersers of the large-seeded motacú palm Attalea princeps, which is the biomass-dominant tree in the Bolivian Amazonian savannas. Macaws dispersed fruits at high rates (75–100% of fruits) to distant (up to 1200 m) perching trees, where they consumed the pulp and discarded entire seeds, contributing to forest regeneration and connectivity between distant forests islands. The spatial distribution of immature palms was positively associated to the proximity to macaws’ perching trees and negatively to the proximity to cattle paths. The disperser role of livestock, presumably a substitute for extinct megafauna, had little effect due to soil compaction, trampling and herbivory. Our results underscore the importance of macaws as legitimate, primary dispersers of large-seeded plants at long distances and, specifically, their key role in shaping the landscape structure and functioning of this Amazonian biome.

Managing forests to meet both production and conservation goals is a growing challenge around the world, particularly as forest areas devoid of human intervention continue to shrink in area. There is a general lack of information about the response of long‐lived vertebrates to silvicultural treatments due to the difficulty of carrying out long‐term studies that can disentangle the effects of forestry from other factors influencing the distribution and numbers of large organisms. We examined the responses of the Cinereous Vulture, Aegypius monachus, to two divergent forestry practices in two colonies where ∼10% of the European population breeds: (1) long‐term exploitation of mature forest in high mountains (highland colony), and (2) clear‐cutting and regeneration in lower altitude mountain areas (lowland colony). Distribution patterns of Cinereous Vultures were determined mainly by forestry and human‐related activities, as well as by orographic variables, whereas forest structure had a lesser influence. Ecological factors such as orography and forest structure had a greater influence in the distribution and abundance of vultures in the highland area, whereas the influence of variables associated with human disturbance was stronger in the lowland area. Vultures in the lowland area consistently selected areas with a low incidence of forestry activity to breed. A major fraction of the variability of breeding success was not explained by the factors considered, although human‐caused disturbance and rainfall during the nestling period had negative effects on breeding success in the lowland colony. The negative effects of forestry activities may persist for a long time, even after the direct impacts of these activities have diminished. In order to effectively conserve breeding areas, it may be necessary to protect suitable habitat from human activity near nests. In addition, halting illegal poisoning is a strict necessity to guarantee the conservation of colonies. Social conflict between conservationists and forest managers who employ local people in nonproductive forestry tasks could easily be resolved by conducting silviculture‐related practices in areas that are unimportant for conservation and directing employment toward activities related to nature conservation.

Theory predicts that contrasting properties of mutualistic and antagonistic networks differentially promote community resilience to species loss. However, the outcome of most ecological interactions falls within a continuum between mutualism and antagonism, and we ignore the extent to which this interactions' continuum might influence community stability. Using a large data set of interactions, we compared co-extinction cascades that either consider or ignore the mix of beneficial and detrimental actions that parrots exert on plants. When the antagonism-mutualism continuum was considered, a combination of the properties that separately enhance community stability in ecological networks emerged. This combination of properties led to an overall increase of the parrot community robustness to face plant species loss. Our results highlight that the conditional outcomes of interactions can influence the structure of ecological networks, thus affecting our predictions of community stability against eventual changes.

Parrots are largely considered plant antagonists as they usually destroy the seeds they feed on. However, there is evidence that parrots may also act as seed dispersers. We evaluated the dual role of parrots as predators and dispersers of the Critically Endangered Parana pine (Araucaria angustifolia). Eight of nine parrot species predated seeds from 48% of 526 Parana pines surveyed. Observations of the commonest parrot indicated that 22.5% of the picked seeds were dispersed by carrying them in their beaks. Another five parrot species dispersed seeds, at an estimated average distance of c. 250 m. Dispersal distances did not differ from those observed in jays, considered the main avian dispersers. Contrary to jays, parrots often dropped partially eaten seeds. Most of these seeds were handled by parrots, and the proportion of partially eaten seeds that germinated was higher than that of undamaged seeds. This may be explained by a predator satiation effect, suggesting that the large seeds of the Parana pine evolved to attract consumers for dispersal. This represents a thus far overlooked key plant-parrot mutualism, in which both components are threatened with extinction. The interaction is becoming locally extinct long before the global extinction of the species involved.

Why avian colonies vary in size and how food competition among nearby colonies a¡ects o¡spring quality are still not completely understood. We simultaneously examined the e¡ects of four scales of breeding density on two measures of o¡spring viability (body condition and T-cell-mediated immunity) in the colonial Magellanic penguin. Body condition of £edglings was inversely correlated with breeding density within 100 m 2 of nests, and decreased with increasing numbers of breeding pairs competing within the parental foraging ranges (100 km), probably as a result of density-dependent food depletion. The T-cell-mediated immune response was positively correlated with body condition, re£ecting, to some extent, the previous breeding-density e¡ects, and was negatively correlated with colony size, which may be related to social stress. However, given the e¡ect of protein intake on cell immunity, this result could also indicate a thus far neglected cost of coloniality, namely the consumption of low-protein food to compensate for the depletion of optimal prey. These results were not in£uenced by other traits, nor by the current exposure of birds to parasites and diseases, as measured by serological variables. Since body condition and the T-cell-mediated immune response of £edgling birds are indicators of their survival and recruitment prospects, the costs we have identi¢ed can explain variability in colony size in relation to food competition with surrounding colonies, as well as the skewed distribution toward small colonies in this species.

Large avian scavengers are among the most vulnerable vertebrates, and many of their populations have declined severely in recent decades. To help mitigate this marked reduction in abundance, supplementary feeding stations (SFS; colloquially termed “vulture restaurants”) have been created worldwide, often without consideration of the scientific evidence supporting the suitability of the practice. SFS have been effective and important tools for conservation and reintroduction of avian scavengers. However, negative consequences can result from large aggregations of individual birds, disrupting intraguild processes and promoting density‐dependent decreases in productivity. At the community level, SFS favor the congregation of predators (ie facultative scavengers), increasing predation risk on small‐ and medium‐sized vertebrates in the vicinity of the SFS. These feeding stations might also affect processes of natural selection and even render populations maladapted to their natural environments. We also examine future scenarios for avian scavengers in relation to ecosystem services, to changes in agro‐grazing economies and in land uses, and ultimately to rewilding landscapes where SFS play a controversial role.

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