DOI: 10.7280/d1cq5v
title: Decomposing an elevational gradient in predation by insectivorous birds

description: Insectivorous birds have ecologically important effects on prey abundance,
 behavior, and evolution, and through top-down control birds indirectly
 reduce herbivory and promote plant growth. While several studies sought to
 characterize biogeographic patterns in top-down control by birds,
 variation in bird predation along elevational gradients is not well
 characterized both in terms of its commonness and the mechanisms
 underlying such variation. Here we characterized variation in bird
 predation along a 700m montane elevation gradient using artificial clay
 caterpillars, assessing the roles of variation in aridity, other
 elevational effects not associated with aridity (e.g., most notably
 growing season length) and bird abundance and diversity. Multivariate
 models revealed attack rates increasing with aridity (when controlling for
 the effects of elevation) and elevation (when controlling for aridity).
 Because aridity declines with elevation, elevational patterns were not
 detectable in a univariate analysis. Bird abundance (but not diversity)
 decreased with elevation (but not aridity) and did not provide an
 explanation for our results, suggesting the underlying mechanisms were
 behaviorally based. We speculate that the declining abundance of insect
 prey with elevation and aridity leads to increased bird foraging efforts
 and thus the likelihood of attacking clay caterpillars. If widespread,
 these dynamics have important consequences for both the interpretation of
 predation bioassays generally and for our understanding of the
 multivariate drivers of variation top-down control by predators and
 predation risks experienced by prey.  
description: Clay caterpillars were placed on aspen trees at 10 sites within a
 valley, at 5 valleys along an elevational gradient in the Rocky Mountains.
 Attack rates by birds were recorded from the clay caterpillars on either 3
 or 4 seperate dates per site. Data of attack are reported as a proportion
 of the 20 caterpillars at 1 site on 1 date that were attacked (76 total).
 We reported aridity as a PCA of temperature and precipiation. We reported
 the bird community using eBird checklists from the same region as the
 valleys, and extracted this following "Best practices for Using eBird
 data". 
description: R Studio
description: # Decomposing an elevational gradient in predation by insectivorous birds
 --- Clay caterpillars were placed on aspen trees at 10 sites within a
 valley, at 5 valleys along an elevational gradient in the Rocky Mountains.
 Attack rates by birds were recorded from the clay caterpillars on either 3
 or 4 separate dates per site. Data of attack are reported as a proportion
 of the 20 caterpillars at 1 site on 1 date that were attacked (76 total).
 We reported aridity as a PCA of temperature and precipitation. We reported
 the bird community using eBird checklists from the same region as the
 valleys, and extracted this following "Best practices for Using eBird
 data". Data on the climate and on the bird community were sourced
 from public databases (PRISM and eBird respectively). The published code
 provides the parameters to which we extracted this data from these public
 sources, and also provides code for how these data were wrangled and thus
 used. ## Description of the data and file structure
 **claycat_writing.csv-** This file contains the data from the sites and
 date where attack rate was recorded. Site: the site number (20 total, in
 each 5 valleys there are 4 sites) Totalattack: the number of attacks out
 of 20 caterpillars at a site and date. Drainage: the name of the valley
 elevation_m: elevation in meters of each of the sites. propattack: the
 proportion of caterpillars attacked out of 20 at a site and date. DaysOut:
 The number of days between recording attacks that the caterpillars were
 exposed. **1_bird_code.R** - Contains the code for extracting community
 data on eBird. We acquired checklists during the month of August 2020 as
 outlined in the code. This code also describes how we derived descriptive
 variables from this data (abundance and diversity) which were subsequently
 used in analyses. **2_climate_data.R** - Contains the code for extracting
 the climate data for our study period from PRISM. We acquired the
 following variables for August 2020: the average precipitation (mm) for
 the month of august 2020 (when attack data was collected), the minimum
 temperature (degrees C) for the month of august 2020 (when attack data was
 collected), the maximum temperature (degrees C) for the month of august
 2020 (when attack data was collected), the mean temperature (degrees C)
 for the month of august 2020 (when attack data was collected). Using this
 data, as outlined in the code, we created a PCA of these four variables
 and extracted the 1st principle component of this analyses, which was
 subsequently used in analyses as a metric of aridity. ## Sharing/Access
 information This is a section for linking to other ways to access the
 data, and for linking to sources the data is derived from, if any. Data
 was derived from the following sources: * ebird.org *