DOI: 10.5061/dryad.15dv41p20
title: Changing patterns of nest predation and predator communities along a tropical elevation gradient

description: Tropical montane communities host the world’s highest beta diversity of
 birds, a phenomenon usually attributed to community turnover caused by
 changes in biotic and abiotic factors along elevation gradients. Yet,
 empirical data on most biotic factors are lacking. Nest predation is
 thought to be especially important because it appears to be common and can
 change selective pressures underlying life history traits, which can alter
 competitive interactions. We monitored 2,538 nests, 338 of which had known
 nest predators, to evaluate if nest predation changes along a tropical
 elevational gradient. We found that nest predation decreased with
 elevation, reflecting the loss of lowland predators that do not tolerate
 colder climates. We found different “super” nest predators at each
 elevation that accounted for a high percentage of events, suggesting that
 selection pressures exerted by nest predator communities may be less
 diffuse than has been hypothesized, at least for birds nesting in the
 understory.
description: <em>Field Sites
 description and Data collection</em>
 Nesting data were collected
 through fieldwork conducted between 2008 and 2014 along the elevational
 gradient of the Kcosñipata
 Valley, located on the eastern slope of the Andes in southeast Peru
 (Figure 1). Between August and December each year, we visited four study
 sites, the Pantiacolla
 Lodge (Lowlands; -12.6420288, -71.2392228; 412 m), the Tono River
 (Foothills; -12.9562228 , -71.4816398; 950–1,000 m), the Cock-of-the-Rock
 Lodge (Mid elevations; -13.055389, -71.546806; 1100-2000
 m) and the Wayqecha
 research station (Highlands; -13.175028, -71.587389;
 2,300-3,100 m). At each
 study site, crews of 4–6
 volunteers searched for nests six days per week, ten hours per day. All
 study sites are connected by continuous forest, representing one of the
 last elevational gradients with continuous forest between 300 and 3100 m
 remaining in the Andes. For additional details about the study sites, see
 Londoño et al. (2015) and Sanchez & Londoño (2016).
 At
 each study site, crews of 4–6 volunteers searched for nests six days per
 week, ten hours per day. A unique plot of 10 to 15 hectares was assigned
 to each volunteer. Upon discovery, nests were monitored using one of three
 techniques, largely based upon immediate availability of equipment;
 nonetheless, all species and all elevations were monitored with the three
 techniques in similar proportions. 1) A thermocouple connected to a U-12
 HOBO data logger (Onset Computer Corporation, Pocasset, MA, USA,
 http://www.onsetcomp.com) was placed inside the nest to record nest
 activity by measuring temperature every minute. 2) A Reconyx PC85 or R60
 Rapidfire professional color IR camera trap (Reconyx, WI, USA,
 https://www.reconyx.com) was placed on a tripod located ~50–100 cm from
 the nest and covered with vegetation to reduce its visibility. Cameras
 were programmed to take 10 photos with every movement at the nest, and
 simultaneously one photo every minute to capture slow-moving predators
 such as snakes. Cameras remained at the nest until it became inactive due
 to predation or nestling departure. 3) Visual (in-person) checks every
 three days during the egg stage and daily (or sometimes every other day)
 during the nestling stage, until the nestlings were preyed upon or fledged
 from the nest. At the end of the monitoring period, each nest was assigned
 one of three possible fates: failed, successful or preyed upon. Failed
 nests were those with eggs that did not hatch or with nestlings that died
 for reasons other than predation. Successful nests were those with active
 and fully feathered nestlings that disappeared between one visit and the
 next. Preyed-upon nests were identified through camera trap images or, if
 the nest was monitored using a thermocouple or in-person visits, through
 discovery of a destroyed nest or an empty nest at a stage when fledging
 was not a possibility. We acknowledge that these techniques may bias
 estimates of predation rate, but any such biases are likely homogeneous
 across sites, allowing us to infer the shape of the relationship between
 elevation and nest fate. Although we were able to recognize predation
 events using all three monitoring methods, predators were identified only
 for those nests monitored using camera traps. Predators were identified to
 species when possible. In cases in which we were unable to identify a
 predator to the species level, we classified it to the lowest taxonomical
 rank possible and assigned it to a morphospecies. Predator identities to
 the species or morphospecies level were used to estimate the change in
 predator diversity and predator turnover along the elevational gradient.
 For analyses to determine how the most common types of predators may
 change with elevation, predator species or morphospecies were placed into
 one of seven predator categories: invertebrates, reptiles, birds,
 marsupials, rodents, primates, and other mammals.
description: Microsoft Excel