Proximate Cues for a Short‐Distance Migratory Species: an Application of Survival Analysis

Abstract

Investigation of bird migration has often highlighted the importance of external factors in determining timing of migration. However, little distinction has been made between short‐ and long‐distance migrants and between local and flight birds (passage migrants) in describing migration chronology. In addition, measures of food abundance as a proximate factor influencing timing of migration are lacking in studies of migration chronology. To address the relationship between environmental variables and timing of migration, we quantified the relative importance of proximate external factors on migration chronology of local American woodcock (Scolopax minor), a short distance migrant, using event‐time analysis methods (survival analysis). We captured 1,094 woodcock local to our study sites in Michigan, Minnesota, and Wisconsin (USA) during autumn 2002–2004 and documented 786 departure dates for these birds. Photoperiod appeared to provide an initial proximate cue for timing of departure. Moon phase was important in modifying timing of departure, which may serve as a navigational aid in piloting and possibly orientation. Local synoptic weather variables also contributed to timing of departure by changing the rate of departure from our study sites. We found no evidence that food availability influenced timing of woodcock departure. Our results suggest that woodcock use a conservative photoperiod‐controlled strategy with proximate modifiers for timing of migration rather than relying on abundance of their primary food, earthworms. Managing harvest pressure on local birds by adjusting season lengths may be an effective management tool with consistent migration patterns from year to year based on photoperiod.

Timing of seasonal migration in mule deer: effects of climate, plant phenology, and life-history characteristics

“…The acquisition of continuous data on timing of migration or other life-history events under field conditions is challenging and sometimes impossible to achieve (Garrott et al 1987, Pulido 2007, Meunier et al 2008, unless animal location data are obtained from collars with global positioning system technology (White et al 2010). Because of logistical constraints, we were unable to monitor presence or absence of mule Notes: Extrinsic factors in interval-censored models for autumn migration with individual covariates included: daily snow depth (PC1), daily temperature (PC3), daily snowfall and precipitation (PC4), daily metric of change in temperature (PC5), quadratic time trend (T and TT), and year (Year).…”

“…The usual technique for coping with the absence of known dates of life-history events has been to assign the event date to the median date within the interval the event was known to occur (Nelson 1995, Sabine et al 2002, Meunier et al 2008. That procedure, however, often underestimates variance, may affect the estimates of regression parameters, and thus, bias their interpretation (Johnson et al 2004, Fieberg and.…”

“…Despite the marked variability in the timing of migration among individuals within a single population (Brinkman et al 2005, Grovenburg et al 2009), seasonal migration often is interpreted at the population level by using point estimates or thresholds in relation to summarized weather patterns. Consequently, the distribution of migratory events among individuals within a season has received little attention until recently (e.g., Meunier et al 2008. Failure to incorporate the broad range of heterogeneity in timing of migration among individuals likely has hampered our understanding of the factors that affect the phenological patterns of migration of large herbivores.…”

American woodcock migratory connectivity as indicated by hydrogen isotopes

“…Some woodcock arrive on wintering grounds in October, whereas winter abundances usually peak in mid‐December (Roberts ) and the northern limit of wintering habitat is variable among and within years (Roberts ), suggesting that woodcock use a range of fall migration strategies. Mixing during migration or winter may confound the north‐to‐south progression of autumn departure based on latitude (Myatt and Krementz , Meunier et al ) and would explain why the linear regression of encounter and banding location latitude of 341 pre‐season‐banded and winter‐encountered juvenile woodcock does not provide evidence of a leapfrog migration strategy. Furthermore, limited departure data and band recoveries (only ∼200 recovered from 1939 to 2010) from Canada make it difficult to examine migration strategies used by woodcock in the most northerly portions of their range.…”

Cues and the optimal timing of activities under environmental changes

“…2008; or leaf flushing: Williams et al. 2008), moon phase (migratory departure: Meunier et al. 2008; spawning of holothurians: Mercier et al.…”