Results
In assigning the bird species to foraging niches, we have followed
procedures proposed by Pigot et al. (2020) based on a standardized
protocol for foraging niche delimitation. Thirty niches were identified
for all of the approximately 10,000 bird species of the world. Of these
six major foraging niches were categorized as Aquatic with three more
chosen by us to accommodate the 49 water bird species of this study,
darters and dippers excluded. The 12 land bird species could be grouped
into two niches: Ground Feeding and Aerial/Sally (Table 2).
We found a significant difference between the deflection parameter
medians of aquatic (260.106) and land
(1595.106) bird foraging niches (p <
0.001), thereby demonstrating an evolutionary distinction between these
groups. There was no significant difference between the deflection
parameters of the two land bird foraging niches (p = 0.600),
Ground Feeding (1228.106) and Aerial/Sally
(2864.106), which indicates similarity among land
birds. The aquatic bird species however, expressed significant
differences between Aquatic Dive (328.106) and Aquatic
Surface (37.106) (p = 0.012), Aquatic Surface
and Aquatic Plunge (935.106) (p <
0.001), and Aquatic Surface and Aquatic Perch
(276.106) (p = 0.001). These results show that
differences in feather microstructure are identifiable with respect to
differences in aquatic niches.
In order to determine if the foraging niches for aquatic and land birds
explain feather microstructure while accounting for phylogenetic
relationships, a phylogenetic ANOVA approach was followed. The degree of
group aggregation was determined in order to establish if the ANOVA
methodology would be affected by the association between the independent
variable, i. e. foraging niche, and the phylogeny. The results indicated
no significant group aggregation for either aquatic birds (r =
0.468 and p = 0.122) or land birds (r = 0.650 and p= 0.120) which confirmed the statistical reliability of the ANOVA
approach. The phylogenetic ANOVA results demonstrated that there is a
significant difference in feather microstructure between aquatic bird
groups (p = 0.001), regardless of phylogenetic relatedness. In
contrast, no significant difference in feather microstructure for the
two land bird feeding niches was observed (p = 0.971).