While this may be the "first evidence" in the sense of measurements of brain activity, swifts apparently sleeping at 10,000 feet were directly observed 100 year

While this may be the "first evidence" in the sense of measurements of brain activity, swifts apparently sleeping at 10,000 feet were directly observed 100 years ago: https://www.rspb.org.uk/globalassets/downloads/documents/conservation--sustainability/help-swifts/amazing-swift-facts.pdf https://www.rspb.org.uk/globalassets/downloads/documents/con...