DOI: 10.5061/dryad.4tmpg4f6r
title: Aggressive interactions between cavity nesting birds in SE QLD Australia

description: 1. Context: A mechanistic understanding of the drivers of competition
 between species at a community level can improve invasive species
 management by helping identify where and when impacts are likely to be
 greatest. Invasive cavity-breeding birds provide a way to test shared
 traits and resource requirements are related to intensity of competition.
 Australia is home to one of the richest cavity-nesting communities
 globally with over 100 native and introduced bird species requiring
 hollows: but the impact of invasive species on most native communities is
 not well understood.   2. Methods: We examined aggressive
 interactions between birds in large hollow-bearing trees. To explore the
 drivers of aggression, we explored whether more similarly sized birds
 interacted more frequently, whether larger species won aggressive
 interactions more often, and whether cavity-breeding species with similar
 preferences for nesting sites (breeding niche space) interacted more
 frequently.  3. Results: We recorded a total of 48 bird species
 of which 20 are cavity-nesters, and 410 aggressive interactions. These
 interaction networks are dominated by the invasive common myna, the native
 noisy miner (a non-cavity-breeder), and the native rainbow lorikeet
 (Trichoglossus moluccanus), but the common myna won the largest total
 number of interspecific interactions. While on average larger birds won
 aggressive interactions more frequently, there were some important
 exceptions to this finding; the common myna (113 ± 30 g) won more
 interactions (26 interactions won) against the larger native rainbow
 lorikeet (126 ± 44 g; 3 interactions won). Among the cavity-breeding
 birds, species with more similar nest-site preferences were observed
 interacting more frequently.  4. Synthesis and applications: The
 impact of the invasive common myna on the cavity-nesting community is
 greatest for species that are close to the common myna in body size and
 share nest site preferences in tree hollows.  Myna control
 efforts should focus on birds that nest in natural tree hollows.
 Additionally, cavity-nesting species are not immune from the impact of
 native noisy-miner aggression.   
description: <i>Interaction surveys were conducted during 10, one hour
 visits to each of eight survey sites. Sites were chosen based on the
 present of large-hollow bearing trees. </i>
 During a visit to a site, one observer recorded all species that
 visited the focal trees and all interspecies interactions that occurred
 within the focal trees for one hour. Observers were 10-30 m from the study
 trees and used 8 x magnification binoculars. At all sites, we observed
 evidence of nesting including carrying nesting materials into cavities,
 cavity excavation, carrying food into cavities and the presence of
 fledglings coming and going from cavities. We recorded all interactions
 between two or more species, with interactions defined as one species
 flying at or within 50 cm of another species. For each interaction, we
 recorded the species and the number of individuals involved, which species
 initiated the interaction and which species was the recipient. For each
 individual in each interaction, the behaviour was recorded (swoop,
 contact, chase, fight or physical contact, threat, displace, avoid), and
 an outcome was determined for each species (win, lose). A loss was
 determined if a species flew from its location. If the recipient species
 showed no response (no alarm call, no movement toward or away from the
 initiating species) it was considered a “win” for that species and a
 “loss” for the species that initiated the interaction.
description: The data is organized as interacting species pairs in order to
 caclulate the win-lose network graph, with the winner and loser of each
 interaction are noted. The data was organized following recommendations
 for the open source program "Gephi", the documentation of which
 can be found in the following link (https://gephi.org/publications/gephi-bastian-feb09.pdf).