This post will be updated as new information becomes available.
Bird collision victims from a Chicago building, 5 October 2023, Field Museum. Photo courtesy of Daryl Coldren.
Our colleagues and friends in the Chicago, Illinois area have sad news about a major bird collision event that occurred last night and this morning, 4-5 October 2023. Reports from the area indicate that large numbers of birds died in collisions while major migration was occurring in the area (see the following checklist, as well as this one). Although details are still emerging, this event appears to be a combination of high intensity migration, adverse weather conditions for flying, and light and glass – a mix we know too well can be deadly.
Please note: we urge all businesses, building owners, and private residences, as well as operators of any illuminated structures, to heed lights out warnings for non-essential lights to be turned off during the migration season – this includes this evening in the Chicago and northern Illinois area, 5 October 2023. Additionally, birders and other concerned parties should be watchful for injured or trapped birds and request help from Chicago Bird Collision Monitors (or act safely if assistance is not available) to help save injured or trapped birds. And equally or more important, we urge all building and homeowners that have not already done so to employ bird friendly designs, whether it is in the glass you install or the treatments on your windows.
On-the-ground observations
- Observers Jacob Drucker, Marky Mutchler, and Lila Fried counted 134,000 birds passing Promontory Point in an hour: https://ebird.org/checklist/S151491365
- Observer Nathan Goldberg reported “utter madness” of 120,000 warblers from his porch in northern Chicago: https://ebird.org/checklist/S151490192
- Exceedingly high numbers of collisions in urban Chicago, especially from buildings with lights on:
Bird collision victims from a Chicago building, 5 October 2023, Field Museum. Photo courtesy of Taylor Hains.
An Ovenbird collision victim found on Chicago streets on 5 October 2023. Photo courtesy of Jorge Garcia.
- Sightings of dead and injured birds from residences, including these photos from Evanston homeowners:
Injured and dead birds found by homeowners in Evanston, Illinois on 5 October 2023.
What happened
High intensity bird migration occurred in portions of the Upper Midwest, highlighted by the intense white area west of Lake Michigan in the BirdCast Live Migration Map below. Notice large areas of low to no migration farther to the east and south – these areas were experiencing or had just experienced significant storms with heavy rains, conditions that are adverse, unfavorable, and at times dangerous for flying.
The adverse weather conditions were associated with a frontal boundary (in blue triangles in the synoptic weather map showing surface conditions pre-dawn in the area below) between cold and warm air masses passing through the region, with more favorable conditions “behind” (to the west) of the boundary, and much less favorable conditions “in front” of the boundary (i.e. to the east).
Digging a little deeper into the radar data from the Chicago radar, below is a four panel snapshot from RadarScope showing imagery from pre-dawn. Note that birds and intense precipitation overlap, dramatically, especially apparent in the upper left panel showing reflectivity (other panels also show this, including the velocity, upper right; classification algorithm output, bottom left showing much gray – biology; and lower right, correlation coefficient showing much blue, values indicative of birds, and red, values indicative of precipitation).
In the image below from the BirdCast Migration Dashboard from Cook County, Illinois for the 4-5 October 2023 night, note specifically the birds in flight and altitude plots on the left: numbers of birds increase dramatically in the second half of the night and altitude of migration decreases dramatically. Birds were generally migrating toward the frontal boundary passing through the region and likely overtook the boundary given their speeds and direction of movement.
To reiterate: we urge all businesses, building owners, and private residences, as well as operators of any illuminated structures, to heed lights out warnings for non-essential lights to be turned off during the migration season – this includes this evening in the Chicago and northern Illinois area, 5 October 2023. Additionally, birders and other concerned parties should be watchful for injured or trapped birds and request help from Chicago Bird Collision Monitors (or act safely if assistance is not available) to help save injured or trapped birds. And equally or more important, we urge all building and homeowners that have not already done so to employ bird friendly designs, whether it is in the glass you install or the treatments on your windows.
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Update 1pm ET, 9 October 2023: As an addendum to this post, we report some preliminary totals for the numbers and diversity of collision casualties, courtesy of Dave Willard, Ben Marks, and the Field Museum Collections staff. This does not represent the full list of species or collision victims.
