Effects of Population Size on Singing Behavior of a Rare Duetting Songbird

Abstract

Although the genetic and ecological effects of population declines in endangered species have been well studied, little is known of the social consequences. Changes in signaling behavior may result in disrupted communication and affect both reproductive and conflict-resolution activities. The North Island Kōkako (Callaeas wilsoni) is an endangered, duetting (i.e., alternating, coordinated singing by mated pairs) songbird endemic to New Zealand temperate rain forests. Scattered populations (approximately 1500 individuals in 13 surviving and 11 translocated populations) in isolated conservation areas of different sizes have been rescued from extirpation and are currently recovering. We examined key song attributes of the Kōkako to assess whether population size or growth rate are related to song complexity, the reduction of which may compromise effective communication. We analyzed song repertoire size and phrase-type sharing (i.e., Jaccard index of similarity), vocal performance (singing rates, song switching rates, and diversity of phrase types), and song syntactical characteristics (i.e., unpredictability in sequences of phrase types) in surviving and translocated populations (populations of approximately 19-250 territorial individuals). Population size was positively correlated with a population's song repertoire, song diversity, and switching of song phrase types and negatively correlated with shared phrase types and variation in syntactical structure of songs. Population growth rate correlated positively with pair repertoire size, population repertoire size, and singing rates during song bouts. As for solo-singing species in fragmented landscapes, songs in the fragmented populations of Kōkako appear to be undergoing microevolution as occurs in island colonization events. Our results suggest that vocal changes in small populations could affect population establishment and growth, particularly in multiple-source translocations. We believe measurement of vocal behavior could be used as a supplement to periodic population censuses to allow more frequent monitoring of population size.

Estimating population size using single‐nucleotide polymorphism‐based pedigree data

“…; Dochtermann and Peacock ; Valderrama et al. ) and practically indispensable for management and conservation (Katzner et al. ).…”

“…Estimates of the population size and its fluctuations are often fundamental for understanding ecological, behavioral, or genetic processes (Ojaveer et al 2004;Dochtermann and Peacock 2013;Valderrama et al 2013) and practically indispensable for management and conservation (Katzner et al 2011). This includes estimates of both effective and true population size, where the former is usually based on genetic data and models, while the latter typically use some form of census data, sometimes genetic.…”

Song sharing and diversity in the Bering‐Chukchi‐Beaufort population of bowhead whales (Balaena mysticetus), spring 2011

“…While changes in technology through time have expedited the sound analysis process, they have not improved detection rates in any way that would explain this change in number of songs in the spring. Rather, it is possible that the increase in song diversity is simply linked to the increase in population size as has been shown in some bird species (Laiolo et al 2008, Valderrama et al 2013. The size of the BCB population has increased by nearly a factor of four since the early 1980s: from~4,200 in 1983 to~8,200 in 1993, tõ 17,000 in 2011 (Krogman et al 1989, Raftery and Zeh 1998).…”

“…, Valderrama et al . ). The size of the BCB population has increased by nearly a factor of four since the early 1980s: from ~4,200 in 1983 to ~8,200 in 1993, to ~17,000 in 2011 (Krogman et al .…”

Conservation implications of song divergence between source and translocated populations of the North Island Kōkako

“…Divergence in the number of unique phrase types may to some extent also depend on the current sample sizes for both source and translocated populations; more sampling could have discovered more unique phrase types. Recent evidence shows that there is a positive correlation between population size and song characteristics such as repertoire size and diversity, and a negative effect of population size on song sharing and syntactical structure in longer-isolated surviving populations as well as translocated populations of k okako (Valderrama, Molles & Waas 2012). Alternatively, divergence of vocal repertoire composition among source and translocated populations could have developed over the 5-8 years of separation.…”