Optimizing surveys for marsh songbirds: does timing matter?

Abstract

Analysis of data from point counts, a common method for monitoring bird population trends, has evolved to produce estimates of various population parameters (e.g., density, abundance, and occupancy) while simultaneously estimating detection probability. An important consideration when designing studies using point counts is to maximize detection probability while minimizing variation in detection probability both within and between counts. Our objectives were to estimate detection probabilities for three marsh songbirds, including Marsh Wrens (Cistothorus palustris), Swamp Sparrows (Melospiza georgiana), and Yellow-headed Blackbirds (Xanthocephalus xanthocephalus), as a function of weather covariates and to evaluate temporal variability in detection probability of these three species. We conducted paired, unlimited radius, 10min point counts during consecutive morning and evening survey periods for our three focal species at 56 wetlands in Iowa from 20 April to 10 July 2010. Mean detection probabilities ranged from 0.272 (SE = 0.042) for Marsh Wrens to 0.365 (SE = 0.052) for Swamp Sparrows. Time of season was positively correlated with detection probability for Swamp Sparrows, but was negatively correlated with detection probability for Yellow-headed Blackbirds, suggesting that detection probability increased during the breeding season for Swamp Sparrows and was highest early in the breeding season for Yellow-headed Blackbirds. Understanding how detection probabilities of marsh songbirds vary throughout the breeding season allows targeted survey efforts that maximize detection probabilities for these species. Furthermore, consistent detection probabilities of marsh songbirds during morning and evening survey periods mean that investigators have more time to conduct surveys for these birds, allowing greater flexibility to increase spatial and temporal replication of surveys that could provide more precise estimates of desired population parameters.RESUMEN. Optimizando el muestreo de aves de pantano: es importante el tiempo en el que se hace? El an alisis de datos de puntos de conteo, un m etodo com un para el monitoreo de tendencias poblacionales en aves, ha evolucionado con el fin de producir estimados de varios par ametros poblacionales (e.g., densidad, abundancia, ocupaci on), estimando simult aneamente la probabilidad de detecci on. Una consideraci on importante en el diseño de estudios que usan puntos de conteos es maximizar la probabilidad de detecci on y minimizar la variaci on en la probabilidad de detecci on dentro y entre conteos. Nuestros objetivos fueron la estimaci on de la detecci on de probabilidad en tres especies de aves paseriformes de pantano, incluyendo Cistothorus paulstris, Melospiza georgiana y Xanthocephalus xanthocephalus como una funci on de covariables clim aticas y la evaluaci on de la variabilidad temporal en la probabilidad de detecci on de estas tres especies. Realizamos conteos pareados sin limite de radio y de 10 minutos de duraci on durante periodos de muestreo consecutivos en la ...

Detection and density of breeding marsh birds in Iowa wetlands

“…Previous work has examined the detection probability of marsh birds and how several factors influence detection of different species [23,50,52,66], and our study further highlights variables that should be considered when surveying for breeding marsh birds. Of particular concern is the experience of observers [87,88].…”

“…Detection probability varies among avian species, and this is particularly true for breeding marsh birds [52,82,83]. We expected cryptic species such as the Virginia Rail to have the lowest detection probabilities, while more vociferous species such as Yellow-headed Blackbirds and Marsh Wrens would have higher detection probabilities.…”

“…While we did not record call types of these species, these species also make a variety of calls, and they can change as the breeding season progresses [52]. Yellow-headed Blackbirds, for example, tend to sing less once young have fledged, so during this phase the probability of detecting this species given it was present likely declined [52].…”

“…In Iowa, published studies have estimated the detection probability and density of several marsh bird species across the state [50][51][52], but none have attempted to obtain estimates particular to restored and pre-restored wetlands. The Shallow Lakes Restoration Project (SLRP) is focused on restoring shallow lakes throughout the Iowa PPR in order to improve conditions for wildlife.…”