Identification of Summer Origins of Songbirds Migrating through Southern Canada in Autumn

Stable hydrogen isotopes (δD) in flight feathers were measured to investigate the summer origins of five species of boreal-breeding warblers captured during fall migration at Canadian Migration Monitoring Network (CMMN) stations spread across southern Canada. Mean δD varied among stations and species within stations, but there was broad overlap in δD values. Although isotope ratios indicate that migrants at each station come from a wide range of latitudes, they are unable to provide much longitudinal discrimination. Band recoveries are sparse, but indicate that in general western Canadian warblers move southeast in fall, eastern birds move southwest, and there is a transition zone in the Great Lakes region. Combining knowledge of migratory direction with isotope results increases discrimination of breeding areas. Isotope results support fall migratory movements by Blackpoll Warbler (Dendroica striata) and Northern Waterthrush (Seiurus novaboracensis) that are more easterly than for other species, and in all study species, birds from more northern regions passed through southern Canada later in the season. Migration monitoring stations capture birds from broad areas of latitude, and migrants passing through each province appear to come from largely different portions of the Canadian breeding range, so a few stations placed in each province should suffice collectively to sample birds from most of the boreal forest. Migration monitoring in southern Canada, therefore, has the potential to monitor status of boreal forest birds in Canada that are unsampled by other monitoring programs.

Threshold detection: matching statistical methodology to ecological questions and conservation planning objectives

Two types of ecological thresholds are now being widely used to develop conservation targets: breakpoint-based thresholds represent tipping points where system properties change dramatically, whereas classification thresholds identify groups of data points with contrasting properties. Both breakpoint-based and classification thresholds are useful tools in evidence-based conservation. However, it is critical that the type of threshold to be estimated corresponds with the question of interest and that appropriate statistical procedures are used to determine its location. On the basis of their statistical properties, we recommend using piecewise regression methods to identify breakpoint-based thresholds and discriminant analysis or classification and regression trees to identify classification thresholds.