The Bluff: May 9-13, 2022

Overview:

Efforts on May 13 were hampered by a sudden and intense onset of Covid-19 symptoms. Unfortunately further flights on May 14 and May 15 were undocumented.

Generally, May 9 had significant numbers of "behind schedule" birds undertaking Continuation Flights and/or were true Diurnal Migrants. A mass-arrival of local breeding species such as Indigo Bunting or Baltimore Oriole occured on May 10, leading to peak numbers of birds undertaking local Geographic Reorientation flights. These flights continued in lower numbers each passing day as (presumably) the "backlog" of local migrants was reduced (i.e., birds were settling into local territories). As migration shifted to a more "ahead of schedule" state, there is no significantly corresponding increase in late-season migrants such as Cape May Warbler or Blackpoll Warbler presumably because:

They are not "late" and are therefore not triggered to undertake a continuation flight.
They do not need to undertake any north-south or east-west local reorientation due to their ultimately destination lying well north of the survey location.

Study at this location over time has provided unique insight, where birds moving in opposite directions (even of the same species) vary in intensities during the spring migration season. This long-duration event helped refine these theories.

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Notable Species:

Blue Jay

Key notes: primarily diurnal migrants; however, increasing local reorientation noted each day.

May 9: 4000 - northbound flight
May 10: 1500 - northbound flight (estimate as birds were generally ignored)
May 11: 1500 - probably many more, going north, were missed. Southbound flight now light but steady with small groups.
May 12: 1200 - still mostly the northbound flight (ignored) but increasing numbers south.
May 13: 800 - estimate

This species undertakes very large diurnal migrations along the south shore of Lake Huron. The Bluff is not an ideal location to count or observe this movement (going east and then northeast as they round the lake). Numbers decrease daily due to a reduction in "backlog" of migrants, and also after several suitable days of migration weather, a low but increasing number were readily detectable undertaking localized Geographic Reorientation Flights back south (or rounding the lake to go west), possibly fine-tuning movements to their summer territories? Late season observations of Blue Jay at this location have a high percentage of southbound birds indicating this trend shift would likely have continued into May 14-15.

Yellow-rumped Warbler

Key notes: primarily through Continuation Flights.

May 9: 153 - all but one going north
May 10: 60 - roughly two-thirds north
May 11: 14 - most north
May 12: 25 - most north
May 13: 8

Numbers peak during the strong onward migration from May 9, decreasing each day as (presumably) fewer birds remain "behind" schedule after multiple nights of strong migratory movement. There is no significant movement of localized reorientation in following days, likely due to few local YRWA territories (i.e., almost all nest north of this location). Low numbers going south may still be localized reorientation (i.e., into Michigan) or perhaps also involve some birds which are exhibiting "True Diurnal Migration" tendencies and are simply flying into the wind. Regardless, it is the continuation flight drive that leads to peak flights at this location.

Baltimore Oriole

Key notes: significant shift from continuation migrants to significant localized reorientation.

May 9: 298 - mostly north
May 10: 1810 - mostly south
May 11: 1109 - mostly south
May 12: 462 - mostly south
May 13: 542 - mostly south

On May 9, migration was still generally "behind" schedule, with migrants (apparently) still moving deliberately north in an apparent Continuation Flight. By May 10, a significant arrival produced birds which needed to undertake Geographic Reorientation flights into their summer territories, leading to a dramatic increase in the number of birds moving south (or west). As migration began to "catch up" on May 11-13, a decreasing number of birds were "remaining" to make these Geographic Reorientation flights (i.e., once a population is on-territory, subsequent suitable flights have a smaller available pool of "migrants" to undertake flights). Lower numbers of orioles moving north may be "reorienting" in the other direction, or could still be "late" continuation migrants. Similar patterns are noted in other locally-nesting species such as Rose-breasted Grosbeak, Indigo Bunting and to a lesser extent Yellow Warbler.

Glossy Ibis

May 12: 1 - south

As an obvious vagrant or overshoot species, there is reason to consider this bird as a notably southward reorienting bird (i.e., not just local reorientation). Perhaps it arrived in Ontario during the notable movements from May 9-11? Presumably some other "cryptic" individuals of more common species like Baltimore Oriole, Hooded Warbler or Dickcissel were significant overshoots similar to the GLIB.

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