DOI: 10.5061/dryad.5hqbzkh7z
title: Advance social information allows red crossbills (Loxia curvirostra) to better conserve body mass and intestinal mass during food stress

description: Animals prepare for fluctuations in resources through advance storage of
 energy, planned reduction in energy costs or by moving elsewhere.
 Unpredictable fluctuations in food, however, may be particularly
 challenging if animals cannot avoid negative impacts on body condition.
 Social information may help animals to cope with unpredictable resources
 if cues from individuals with low foraging success give advance warning
 about deteriorating conditions. This study investigates the impact of
 social information on behavior and physiology of food-restricted captive
 red crossbills (Loxia curvirostra). Birds were restricted to two short
 feeding periods per day to simulate a decline in resources and were given
 social information from food-restricted neighbors either before (i.e.,
 predictive) or during (i.e., parallel) the food restriction period. Focal
 birds better conserved body mass during food restriction if social
 information was predictive of the decline in resources. Crossbills with
 predictive information ate more food, had larger intestinal mass and
 better conserved pectoral muscle size at the end of the restriction period
 compared to those with parallel social information. These data suggest
 that birds can use social information to alter behavioral and
 physiological responses during food shortage in ways that may confer an
 adaptive advantage for survival.
description: This experiment was organized into a preparative phase during
 which focal birds received social information from well-fed or restricted
 neighbors, followed by a restrictive phase during which focal birds were
 food restricted. Focal birds were provided with social information from
 food-restricted neighbors for either three days prior to their food
 restriction (i.e., Social Predictive focal group) or for three days
 coincident with the focal food restriction (i.e., Social Parallel focal
 group). The total amount of social information received about declining
 food was thus similar between the two focal groups; however, this design
 also resulted in different social information contexts during the
 restrictive phase: predictive focal birds had well-fed neighbors whereas
 parallel focal birds had restricted neighbors. To control for this, I also
 compare the response to food restriction in the neighbor groups. Neither
 of the neighbor groups received predictive information prior to their
 respective restrictions; however, the Predictive Neighbors were housed
 next to well-fed birds during their restriction whereas the Parallel
 Neighbors were housed next to restricted birds.
 <em>Capture and captive conditions</em>
 The red crossbill species is a complex of different eco-types
 that are morphologically adapted to particular species of conifer seeds
 and which can be acoustically identified by type-specific vocalizations.
 This experiment utilizes Type 2 red crossbills, which are found frequently
 in ponderosa pine (Pinus ponderosa) dominant habitats. Ninety-six Type 2
 red crossbills were captured via mist net at various field sites in the
 east Cascade mountain range of Oregon and Washington, USA in late summer
 of 2019. Birds were held in captive facilities at Oregon State University
 on natural photoperiod and room temperature, and with ad libitum pellet
 food and daily sunflower seed treats until the experiment started the
 following summer. All birds were handled once per week for a separate
 experiment that monitored seasonal changes in body condition from March to
 early June. A subset of birds (N = 24) experienced a long-day photoperiod
 exposure for several weeks in late March (see supplement of publication
 for details). These birds were split equally between the Predictive
 Neighbor and Parallel Neighbor groups and we detected no differences in
 initial mass or in their response to food restriction compared to
 individuals that had not previously been photoadvanced.
 <em>Social Information</em> Sex
 and age-at-capture were balanced across all treatment groups in three
 experimental rooms. Focal birds were housed alone in a small cage (42 cm L
 x 30 cm W x 56 cm H) with visual contact with one pair of neighbors housed
 in a cage next to them. Neighbors were the same sex as the focal bird and
 included one juvenile and one adult in each pair. Control individuals were
 visually separated from other birds but could hear the other control
 birds. Similarly, each social group could hear the other individuals of
 their treatment group only (i.e., one treatment group per experimental
 room).  <em>Food Restriction and Food
 Intake</em> Birds were fed a commercial
 maintenance pellet food designed for songbirds (see supplement for
 nutritional information). Controls had access to food ad libitum for the
 entire experiment. Focal and neighbor birds in the social groups each
 experienced 3 days of food restriction during which they had access to
 food for two 45-min feeding sessions per day. Food was provided in a
 covered cup to minimize spills and food intake was calculated as the
 change in grams of food remaining in the cup across a 24-hour period,
 measured with an electronic balance to the nearest 0.01 g. Multiple food
 cups were provided in neighbor cages to ensure both birds had access to
 food during the feeding periods. One bird in the Social Predictive group
 regularly flung food out of its cage, thus food intake was not calculated
 for this bird. <em>Body Condition
 Metrics</em> Body mass was measured with an
 electronic balance to the nearest 0.01 g. Muscle and fat deposit scores
 were collected by a single experienced observer to the nearest 0.25 scale
 unit in a partially blind design. The observer knew the stage of the
 experiment and from which room data were being collected, but did not know
 the bird’s individual identification or if the bird was from a neighbor or
 focal group at the time of scoring. Pectoral muscle size was scored on a
 scale of 1 to 4 based on the shape of the muscle around the keel,
 described by Bairlein in detail. Fat deposits were scored in the abdominal
 and furcular cavities based on Helms and Drury.
 <em>Organ Mass and Carcass Lipid
 Composition</em> Six randomly chosen individuals
 from the Control, Social Predictive and Social Parallel groups were
 euthanized by overdose of isoflurane, plucked free of feathers and
 immediately dissected for wet organ mass measurements immediately
 following the Day 3 sampling session. Another six individuals from the
 Social Parallel group were sacrificed later after having been refed on
 <em>ad libitum</em> food for two weeks to determine how
 intestinal mass in food restricted birds responded to refeeding and to
 help interpret the observed patterns during restriction. I did not sample
 from all groups to reduce the number of birds sacrificed. Wet masses of
 liver, gizzard, esophagus, stomach, intestine and colon were collected
 using an electronic balance to the nearest hundredth of a gram. Alimentary
 organs were each cleared of contents by cutting each structure open with
 surgical scissors, rinsing with water and then blotting dry prior to
 measurement. Organs were immediately placed back in the carcass and the
 carcass was frozen at -80° C . Percent lipid in dried carcass mass was
 determined by Soxhlet extraction (see supplement for details) to test if
 visual scoring of subcutaneous fat stores predicted whole-body lipid
 composition. <em>Activity</em>
 Activity was monitored continuously throughout the experiment
 with infrared activity monitors from STARR Life Sciences (Oakmont, PA,
 USA). These monitors record the number of beam breaks over time and
 capture whole body movements using an array of infrared beams projected
 throughout the cage. Sensor ID and position on the cage were kept constant
 for each individual throughout the course of the experiment to minimize
 any impact of detection variability on changes in activity levels. Monitor
 position ensured that activity was captured from only a single focal
 cage.  Three sensors failed during the experiment (two in the Social
 Predictive and one in the Social Parallel).