Linking biodiversity and ecosystem processes across spatial scales: functional responses of cavity-nesting avian communities to wildfires in andean temperate forests

OBJECTIVE 1. TO TEST IF CHANGES IN AVIAN SPECIES RICHNESS AND SPECIES COMPOSITION, ARE ASSOCIATED WITH FOREST WILDFIRES.

OBJECTIVE 2. TO DETERMINE CHANGES IN THE FUNCTIONAL DIVERSITY OF THE CAVITYNESTING BIRD COMMUNITY ACROSS DIFFERENT DEGREES OF WILDFIRE SEVERITY.

Methods

We selected four treatments according to their fire histories and levels of disturbance: (A) control (unburned; undisturbed); (B) burned once in 2002 (slightly disturbed because it was burned once and it experienced a relatively long-time recovery; sampled 16 years post-fire); (C) burned once in 2015 (moderately disturbed because it was burned once and it experienced a relatively short-time recovery ; sampled two years post-fire); and ( D) burned twice, in 2002 and 2015 (highly disturbed because it was burned twice and it experienced a relatively short-time recovery; sampled three years after the last fire).

Community Ecology Surveys

In each treatment, we established 40 point count stations. During the breeding season (December-February; Ralph et al. 1996), we sampled the control site and the “burned 2015” site in 2016-2019 and the “burned 2002” and “burned 2002-2015” sites in 20172018. Each point count lasted six minutes during which all the birds seen and/or heard within a radius of 50 m were recorded. We recorded temperature (°C), humidity (%) and wind speed (m/s) at each counting point, using a portable meteorological unit. Avian species were classified into guilds according to habitat use, foraging mode, foraging substrate and migratory status. The resultant guilds were related to the use of resources relevant to the ecosystem function (i.e. quantity, type and temporality of the resource used and the strategies of each species to obtain the resources). The response of the guilds to the different burned conditions was compared using generalized linear mixed models (GLMMs). These models describe the relationship between a response variable and a set of explanatory covariates (fixed effects) compiled in units aggregated at different levels (random effects). We tested the fixed effect of the “control”, “burned 2002”, “burned 2015” and “burned 20022015” sites on the observed richness and estimated density of avian guilds (response variables). The sampling season was used as a random effect.

Breeding Ecology Surveys

We searched for and monitored nests of birds and mammals in tree cavities. To confirm nesting (eggs or young) we inserted 1.8-cm diameter video cameras mounted on horizontal rods or flexible silicon tubing, using 15- or 22-m telescoping poles, a ladder, or single-rope tree climbing. For cavities in unstable trees, above the reach of our telescoping poles, we watched during 2-hr sessions to assess the evidence for a nest (e.g. parents delivering food, removing fecal sacs, or remaining in the cavity for long periods of time that coincided with the usual length of incubation bouts for the species). We used the bipartite package to construct 2-way matrices of interactions among substrates (tree species), cavity producers (excavator species + decay), and secondary cavity users (non-excavators). Each cell in the matrices contained the number of interactions between each species pair (number of nests). To quantify structure at the network level, we used the bipartite package to calculate five metrics. To examine how tree species and sizes influenced their use by cavity-nesting birds, we fit Generalized Linear Models (binomial family, stats package) predicting tree use (nest vs. random) from the predictor variables DBH and tree species.