DOI: 10.5061/dryad.m0cfxpp74
title: Vulture culture: dietary specialization of an obligate scavenger

description: Individual dietary variation has important ecological and evolutionary
 consequences. However, it has been overlooked in many taxa that are
 thought to have homogeneous diets. This is the case of vultures,
 considered merely as “carrion eaters”. Given their high degree of
 sociality, vultures are an excellent model to investigate how
 inter-individual transmissible behaviors drive individual dietary
 variation. Here, we combine GPS-tracking and accelerometers with an
 exhaustive fieldwork campaign to identify the individual diet of 55
 griffon vultures (Gyps fulvus) from two Spanish populations that partially
 overlap in their foraging areas. We found that individuals from the more
 humanized population consumed more anthropic resources (e.g., stabled
 livestock or rubbish), resulting in more homogeneous diets. In contrast,
 individuals from the wilder population consumed more wild ungulates,
 increasing their dietary variability. Between sexes, we found that males
 consumed anthropic resources more than females did. Interestingly, in the
 shared foraging area, vultures retained the dietary preference of their
 original population, highlighting a strong cultural component. Overall,
 these results expand the role of cultural traits in shaping key behaviors,
 and call for the need of including cultural traits in Optimal Foraging
 models, especially in those species that strongly rely on social
 information while foraging.
description: GPS-tracking and study
 areas We captured 65 adult griffon vultures, 30
 individuals in Southern Spain between December 2014 and January 2015 and
 35 individuals in Northern Spain between December 2015 and March 2016. The
 Southern area is a mountainous region (500–2,107 m a.s.l.) covered by
 Mediterranean woodlands and pasturelands, where the main human uses are
 traditional farming, hunting, forestry and tourism (44). The Northern area
 is a flat area (28–659 m a.s.l.) surrounded by mid-sized mountains (up to
 1500 m a.s.l.) and highly transformed for intensive agriculture, with
 traditional sheep livestock being replaced by intensive farming (45, 46).
 This leads to more predictable ungulate carrion sources in the Northern
 area compared to the Southern one (30) although trophic resources can be
 considered abundant in both areas. In addition to these areas, both
 vulture populations share a second foraging area in Southwestern Spain
 (Figure 1 and Figure S3) where carrion from wild and domestic ungulates is
 also abundant (42). We sexed vultures by molecular procedures (47).
 We determined age by morphological features (48). All birds were equipped
 with 90 g GPS/GPRS-GSM devices that include accelerometers from e-obs
 digital telemetry. The setting of the GPS/ACC devices varied depending on
 weather conditions and the power level of the batteries (see Table S1).
 Except for those birds that died or whose device failed (N=15), we tracked
 all the vultures between the capture day and December 2018.
 Identification of feeding events and diet
 description For each tracked vulture, we identified
 potential feeding events using Accelerater, a supervised learning
 algorithm (http://accapp.move-ecol-minerva.huji.ac.il/; see (40)) implemented with validated samples recorded
 in feeding stations (26,
 16). We recorded 11,636
 possible feeding events (Figure 1); from these, we visited 4,372 locations
 during fieldwork campaigns, confirming feeding by vultures in 3,338 cases
 (efficiency to locate feeding events: 76.35%). For each event, we
 recorded: i) individual identifier of the vulture/s involved, ii)
 coordinates of the feeding events, grouping them in grids of 10 x10 km,
 iii) the feeding site, classified into seven categories: random (i.e.
 carcasses not associated to infrastructures), hunting property, extensive
 farming, intensive farming, carcass dumping site, landfill, and “other”
 (see Figure 2 for details),  iv) the origin of the carcass, according to
 five groups: livestock, wild, mixed (i.e., carcasses from both livestock
 and wild ungulates found together), rubbish, and other (e.g., dogs, rests
 of human food or unknown carcasses); v) the species to which the
 carcass/es belonged in those cases where it was possible to
 identify. In addition, when access to the feeding sites
 was prevented (e.g., terrain too steep or private property), we identified
 feeding events of GPS-tracked vultures by crossing expert opinion and
 official data on livestock and hunting areas from the Spanish Ministry of
 Agriculture, Fisheries and Food (50, 51). Thanks to this information, we
 identified 1,493 feeding events. Our final dataset is composed of 4,831
 feeding events (Figure 1), representing 41.52% of the total feeding events
 identified by GPS-tracking data. This dataset excludes individuals with
 less than 30 feeding events recorded, being the total number of
 individuals studied was 55, 29 from the Northern population (15 females
 and 14 males) and 26 from the Southern population (11 females and 15
 males). Then, we compared the number of feeding events
 at different feeding sites and with different carrion origin between the
 Northern and Southern populations and between sexes, using chi-square
 tests in R (52).