Quantitative and Qualitative Approaches to Identifying Migration Chronology in a Continental Migrant

Abstract

The degree to which extrinsic factors influence migration chronology in North American waterfowl has not been quantified, particularly for dabbling ducks. Previous studies have examined waterfowl migration using various methods, however, quantitative approaches to define avian migration chronology over broad spatio-temporal scales are limited, and the implications for using different approaches have not been assessed. We used movement data from 19 female adult mallards (Anas platyrhynchos) equipped with solar-powered global positioning system satellite transmitters to evaluate two individual level approaches for quantifying migration chronology. The first approach defined migration based on individual movements among geopolitical boundaries (state, provincial, international), whereas the second method modeled net displacement as a function of time using nonlinear models. Differences in migration chronologies identified by each of the approaches were examined with analysis of variance. The geopolitical method identified mean autumn migration midpoints at 15 November 2010 and 13 November 2011, whereas the net displacement method identified midpoints at 15 November 2010 and 14 November 2011. The mean midpoints for spring migration were 3 April 2011 and 20 March 2012 using the geopolitical method and 31 March 2011 and 22 March 2012 using the net displacement method. The duration, initiation date, midpoint, and termination date for both autumn and spring migration did not differ between the two individual level approaches. Although we did not detect differences in migration parameters between the different approaches, the net displacement metric offers broad potential to address questions in movement ecology for migrating species. Ultimately, an objective definition of migration chronology will allow researchers to obtain a comprehensive understanding of the extrinsic factors that drive migration at the individual and population levels. As a result, targeted conservation plans can be developed to support planning for habitat management and evaluation of long-term climate effects.

Effects of satellite transmitters on captive and wild mallards

“…We defined a transmitter failure or mortality event as the disappearance of signal or consistent and sequential locations that were ≤100 m from the last recorded location for each individual. Elsewhere (Beatty et al ), we reported the migration chronology for each of the wild mallards using net displacement methods (see Bunnefeld et al ), which were used to exclude breeding season movements of marked birds.…”

Identifying critical migratory bottlenecks and high‐use areas for an endangered migratory soaring bird across three continents

“…ND measures the straight line distance between the first location (i.e. the trapping location) and all subsequent relocations for an individual animal (Bunnefeld et al 2011, Beatty et al 2013. We calculated daily ND values for each bird with the first relocation recorded each day.…”

From animal tracks to fine‐scale movement modes: a straightforward approach for identifying multiple spatial movement patterns

“…NSD, which is the Euclidian squared distance between the first location of a segment and any consecutive relocations, is an effective method to characterize GPS data because it transforms movement data from 3D (x, y, t) to 2D (x from origin, t) permitting the application of simpler statistical models (B€ orger & Fryxell 2012). NSD is commonly used to model migratory movement of animals at very large scales (Bunnefeld et al 2011;Singh et al 2012;Beatty et al 2013), but can logically be applied to smaller-scale movements.…”