It is early May – where are our migrant Warblers on their journeys? (Hint: check out the maps below!) The majority of our breeding Warblers are lurking just south of the belt (the Canada/US belt, not the Bible Belt) and ready to explode across, given the right conditions. According to the eBird Oracle, unless you live in southern Ontario, the best is yet to come this migration season! Currently, regional birding listservs are revealing a couple of new species each day, but these might be just the leading edge of the profusion of biomass on its way to Canada. Canadians: prepare to have your soundscapes enriched and your insect-populations managed pro bono.
In my last post, I looked at monthly patterns of movement from downloaded eBird data. However, there is approximately a three-month lag time in the availability of eBird’s downloadable data, so real-time migration maps cannot be made directly from the database. However, regular visits to the eBird web map application can expose near-real-time regional movement patterns…
The maps presented here were created for all Warblers with breeding ranges extending into Canada. For each species, winter (January-February 2013) and current (1 April to 8 May, 2013) eBird observations are provided to give a glimpse of how much movement Warblers have undertaken so far this season and how near each species is to Canadian soil. eBird observation data are represented by purple blocks, with the darkest purple blocks indicating areas of the highest density of reports. NatureServe species distribution polygons are overlaid for reference (credit below; orange = breeding range, blue = nonbreeding range, black = year-round range; rare occurrence points not included). Observations located between breeding and nonbreeding ranges are areas being used during migration. (see more detailed methods at the end of the post).
Take a close look at the patterns: how close is each species to your region? Do these patterns match what you are seeing, and hearing, on the ground? Do the locations of the nonbreeding and overwintering grounds surprise you? Do you think the eBird data reliably delineates the species ranges?
Click the pause button and use the arrows to advance the maps at your own pace. Individual maps in the gallery above can be enlarged by clicking thumbnails below and choosing “view full size”.
There are several considerations required before deciding whether these data represent true species distributions (e.g., timing of submission of reports, species misidentification, gaps in eBirder coverage, species detectability, location of migratory pathways relative to eBirder density, eBirder behaviour), but at broad scales these maps can give fascinating insight into the pathways used and timing exhibited by our migrants.
Keep your eyes and ears peeled in the days to come and enjoy the migration season!
(overview of methods: For each species, screengrabs for each time frame were captured using the free Firefox add-in FireShot, georeferenced in ArcGIS to a boundary file from the North American Atlas (free from Geogratis), NatureServe species distributions (Data provided by NatureServe in collaboration with Robert Ridgely, James Zook, The Nature Conservancy ― Migratory Bird Program, Conservation International ― Center for Applied Biodiversity Science, World Wildlife Fund ―US, and Environment Canada ― WILDSPACE.) were overlaid and symbolized and maps were exported; contact: email@example.com).