Macrogeographic Vocal Variation in Subspecies of Swamp Sparrow

Abstract

Abstract. Variation in song can play a central role in species and subspecies recognition among birds. The ability of individuals to distinguish between songs of their own versus songs of a different subspecies potentially strengthens local adaptation of subspecific populations. We investigated the degree of vocal divergence and discrimination between two subspecies of Swamp Sparrow (Melospiza georgiana) to examine how variation in song could influence behavioral response. We recorded songs of Southern (M. g. georgiana) and Coastal Plain (M. g. nigrescens) Swamp Sparrow males in Maryland and Delaware, respectively, and analyzed variation in syllable composition, repertoire size, trill rate, and frequency bandwidth. In addition to describing differences in song characteristics, we performed an estimate of local song type diversity that predicted larger population repertoires in M. g. nigrescens. We then broadcast recordings to evaluate male territorial responses to song and found that males reacted more strongly to songs of their own subspecies than to songs of the other subspecies. The extent of song variation and discrimination suggests the possibility of continued divergence. Further tests may determine whether such results can be generalized beyond the populations studied to the subspecies level, and whether females as well as males differentiate between songs from separate subspecies. Variación Vocal Macrogeográfica en Subespecies de Melospiza georgianaResumen. La variación del canto puede desempeñar un papel importante en el reconocimiento de especies o subespecies de aves. La capacidad de distinguir entre canto autóctono y alóctono puede reforzar la adaptación local de las poblaciones subespecíficas. Se investigó el grado de divergencia y discriminación vocal en dos subespecies de Melospiza georgiana para examinar la influencia de la divergencia vocal sobre el comportamiento de ambas subespecies. Se grabaron cantos de M. g. georgiana y nigrescens en Maryland y Delaware, respectivamente, y se analizó la variación en la composición silábica, el tamaño del repertorio, la velocidad del canto y el ancho de banda. Además de describir las diferencias en las características del canto entre las dos subespecies, se hizo un cálculo de la diversidad local del canto que predijo un repertorio colectivo más grande en M. g. nigrescens. Después se reprodujeron grabaciones para evaluar la respuesta territorial de los machos al canto y se encontró que la reacción era mayor ante cantos de individuos de la misma subespecie que ante aquellos de la otra subespecie. El grado de variación y discriminación entre cantos sugiere la existencia de un proceso de divergencia entre estas dos subespecies. Sin embargo, es necesario realizar más experimentos para generalizar estos resultados más allá de las poblaciones estudiadas al nivel de subespecies, y para determinar si las hembras también pueden discriminar los cantos de diferentes subespecies.

Interactions between sexual and natural selection on the evolution of a plumage badge

“…We used forehead and cap patch lengths instead of the two principal components for these last two tests, however, as we only had photographs of four of the males from our trials (and therefore could not calculate either patch area or the principal components for the majority of trials). Further, we conducted trials on each male twice (Liu et al 2008), thus we tested for effects on approach distance and time spent near the playback speakers using a repeated-measures ANOVA controlling for the trial type within each individual. Given the small sample size of these trials and the model's nested structure, we constrained model selection to include only those models with two or fewer independent variables.…”

“…Detailed descriptions of the methods of this experiment are described in Liu et al (2008). One of twelve song tapes were randomly selected for broadcast from a camouflaged, mounted speaker placed at the territory edge as determined by previously observed singing locations of the territorial male.…”

Density, Abundance, and Habitat Associations of the Inland Swamp Sparrow (Melospiza georgiana georgiana) in Iowa

“…obs. Droege 1990, Mowbray 1997), breeding season habitat requirements (Greenberg and Droege 1990, Mowbray 1997, Beadell et al 2003, plumage (Greenberg et al 1998), and song (Liu et al 2008). Despite a slightly increasing population trend according to the North American Breeding Bird Survey (BBS; Sauer et al 2014), the Swamp Sparrow is still listed as a species in need of long-term conservation and planning by Partners in Flight (Rich et al 2004).…”

Acoustic Signal Evolution: Biomechanics, Size, and Performance

“…Similarly, the requirement for broad mechanical modulations in the production of wide frequency bandwidth necessarily limits cycle rates and thus realized trill rates. Trade-offs between trill rate and frequency bandwidth have since been described in greater detail for a wide range of songbird species, including swamp sparrows (Ballentine et al, 2004;Liu et al, 2008), dark-eyed juncos (Cardoso et al, 2007), Lincoln's sparrows (Sockman, 2009), yellow warblers (Beebee, 2004), black-throated blue warblers (Colbeck et al, 2010), banded wrens (Illes et al, 2006), and red-winged blackbirds (Cramer and Price, 2007). Similar trade-offs have also been described outside of songbirds, including in two seabirds, the brown skua and the great frigatebird (Juola and Searcy, 2011), in a rodent, the neotropical singing mouse (Pasch et al, 2011), and in bat echolocation calls (Schumm et al, 1991;but see Schmeider et al, 2010).…”