Results
All 29 individuals interacted with at least one other vulture in all
three social situations: co-flight, diurnal, and nocturnal ground
interactions (Fig. 3, Table S1). The centrality of individuals differed
across social situations. Individuals differed in their importance
across social situations in terms of their degree, strength, and
PageRank. For example, a vulture that interacted with multiple vultures
while co-flying did not necessarily interact with as many individuals
while on the ground (Fig. 4).
The centrality of individuals in the aggregate network did not
necessarily reflect their centrality in each social situation. The
degree of individuals in co-flight and diurnal ground interactions were
positively correlated with the degree in the aggregate network
(Spearman’s correlation: co-flight: ρ = 0.78, p-value <
0.0001 and diurnal ground interactions: ρ = 0.68, p-value
< 0.0001; Fig. 5A, 5G). However, degree in nocturnal ground
interactions was not significantly correlated with degree in the
aggregate network (Spearman’s correlation: ρ = -0.17, p-value =
0.38; Fig. 5D). Both strength and PageRank in each of the three social
situations were positively correlated with the strength and PageRank in
the aggregate network (Spearman correlations for strength of
aggregate with: co-flight ρ = 0.44, p-value = 0.02; nocturnal
ground interactions ρ = 0.8, p-value < 0.0001; and
diurnal ground interactions ρ = 0.89, p-value < 0.0001;
Figs. 5B, E, H and Spearman correlations for PageRank of
aggregate with: co-flight ρ = 0.39, p-value = 0.04 ; nocturnal
ground interactions ρ = 0.8, p-value < 0.0001; and
diurnal ground interactions ρ = 0.89, p-value < 0.0001,
Figs. 5C, F, I).
The correlation between centrality in the aggregate network and each
social situation was often different than expected by chance when
compared with the reference models. Degree both in the co-flight and
diurnal ground interactions was positively correlated with the degree in
the aggregate more than expected by chance (Permutation test: co-flight
p-value < 0.0001 and diurnal ground interactions p-value
=0.002; Fig. 6A). However, the correlation between degree in nocturnal
interactions and degree in the aggregate network did not differ from
what was expected by chance (Permutation test: p-value = 0.791; Fig.
6A). Strength in the nocturnal and diurnal ground interactions was
positively correlated with strength in the aggregate network more than
expected by chance (nocturnal ground interactions: p-value = 0.006 and
diurnal ground interactions: p-value = 0.009; Fig. 6B). However,
although the relationship between strength in co-flight and strength in
the aggregate network were correlated (Fig. 5B) this correlation did not
differ significantly from chance expectation (co-flight: p-value = 0.07;
Fig. 6B). PageRank in the nocturnal and diurnal ground interactions was
positively correlated with PageRank in the aggregate network, more than
expected by chance (nocturnal ground interactions: p-value = 0.006 and
diurnal ground interactions: p-value = 0.004, Fig. 6C). However, the
positive relationship between PageRank in co-flight and PageRank in the
aggregate network (Fig. 5C) was not significantly different than
expected by chance (co-flight: p-value = 0.115; Fig. 6C).