Extracting data for latitude, climate, and species’ intrinsic
traits
In order to assess the relationship between survival and latitude, we
recorded the geographic coordinates for each species in each study from
information provided in the paper itself or by locating the study area
on Google Maps. For 26 studies that measured survival over broad spatial
scales, such as at the national or continental level (e.g., the MAPS
dataset; DeSante et al. 2015), we calculated the centroid of the
breeding range for each species within the area specified by the study
with occurrence data extracted from eBird using the auk package
(Strimas-Mackey et al. 2018) in R (v.3.5.3; R Core Team 2019).
This allowed us to estimate a unique latitude and longitude for the
centroid of each species’ realized breeding range rather than simply
selecting an unweighted point in the study area itself. As latitude is
often used as a surrogate for variation in climatic conditions between
the north and south poles, we evaluated the predictive power of three
key extrinsic factors that characterize the environment of a species and
are hypothesized to influence avian survival: annual precipitation
(Rockwell et al. 2017; Shogren et al. 2019), minimum
winter temperature (Robinson et al. 2007; Salewski et al.2013), and temperature seasonality (Ricklefs 1980; Lloyd et al.2014). We also tested whether
species’ intrinsic traits explained global patterns in avian survival
rates by collecting data on body mass, clutch size, and species’
migratory habit, which we obtained
from information contained in the paper, published reference databases
(i.e., Jetz et al. 2008 for clutch size; Wilman et al.2014 for body mass; Barçante et al. 2017 for migration), or the
Handbook of birds of the World Alive (del Hoyo et al. 2018).
Further details describing our data compilations methods are available
in Supporting Information S2.