Abstract
Louisiana Waterthrush (Parkesia motacilla) is a familiar singer in the Western Hemisphere family Parulidae, yet apparent geographic variations in its song and potentially related causal mechanisms have not received detailed examination in previously published studies. Here, we analyzed song pattern variations of 651 Louisiana Waterthrush singers in audio spectrogram recordings obtained from our field work and publicly accessible bioacoustics archives. Visual and auditory assessment of the introductory note sequence of each song identified three distinct song types (A, B, and C) and most of the songs were assigned to one of these types. Linear Discriminant Analysis and Random Forest methods were used to verify the assignments and showed strong agreement for Type A with slightly less agreement on Types B and C. User error rates (proportion of the Linear Discriminant Analysis classifications that were incorrect) were low for Types A and B, and somewhat higher for Type C, while producer error rates (proportion of the song type for which the Linear Discriminant Analysis was incorrect) were somewhat higher for Types A and C than the minimal levels achieved for Type B. Our findings confirmed that most between-individual variation was in the number of notes and note sequence duration while most within-individual variation resulted from the percent of downstrokes. The location of each singer was plotted on a map of the breeding range and results suggested the song types have large-scale discrete geographic distributions that co-occur in some regions but not range-wide. Evaluation of the distributions provided tentative support for a hypothesis that two of the song types may independently exhibit congruence with the geographic extent of Pleistocene glacial boundaries and the third song type may be distinguished by a lack of congruence, but further investigation is needed to elucidate whether the song variations represent subpopulations with three separate evolutionary histories.
Highlights
The Louisiana Waterthrush (Parkesia motacilla) is unique among Parulidae as the only bird in the southeastern United States that breeds exclusively along forested streams [1]; prime habitat consists of narrow linear corridor territories along uncontaminated headwater streams in unfragmented mature forest with open understory and an optimal percentage of 30–69% deciduous species [2]
The INS portion of most Louisiana Waterthrush songs consisted of a repetitive series of one of three note shape types that were assigned as Type A, B, or C
Within the broader structure of each type’s note shapes, there was considerable variance between individual singers in note sizes and dimensions. This individuality within the species’ songs allowed for a multitude of singers to be identified and catalogued from the burgeoning supply of publicly available audio spectrograms, offering a largely untapped opportunity to study lineages and dispersal tendencies through unique song variations that are presumably culturally transmitted between generations
Summary
The Louisiana Waterthrush (Parkesia motacilla) is unique among Parulidae as the only bird in the southeastern United States that breeds exclusively along forested streams [1]; prime habitat consists of narrow linear corridor territories along uncontaminated headwater streams in unfragmented mature forest with open understory and an optimal percentage of 30–69% deciduous species [2]. It is common for both males and females to return to their same territory in consecutive years [3]. Two juveniles banded by Eaton [4], were documented 2.0 km and 4.8 km from their natal areas just over a month after leaving the nest
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