•  
  •  
 

Predicting Evening Departure Times of an Eastern Screech Owl (Megascops asio) from its Daytime Resting Site

Abstract

The circadian clock of birds is cued by light, but how tightly is it set to human-devised designations of brightness? I tested this from 21 July through 2 November 2025 (n = 87 observations) by recording when an adult Eastern Screech Owl (Megascops asio) left its nestbox in the evenings at Longboat Key, a barrier island off Florida’s southwestern coast (~27° 24’ 45” N | 82° 39’ 32” W), and calculated how closely these times correlated with sunset and readings taken with a handheld off-the-shelf photometer (“luxmeter”). I also assessed whether departure times were affected by crepuscular sky condition (clear or cloudy). Results showed high correlation with sunset (R2 = 0.99). In contrast, photometer readings and sky condition were poor proxies for departure time. Most photometers are designed for daytime and indoor use, and the dim light commonly encountered by biologists during field work can be orders of magnitude below their detection limits. Better ones that are affordable are needed. I advocate standardizing the units by which light levels are measured. A common mathematical language is needed in which the units applied in biology, astrophysics, and astronomy are compatible, bringing together scientists from all disciplines who study how natural light and the unnatural brightness caused by anthropogenic visual pollution affect crepuscular and nocturnal skies and the life they shelter.

This document is currently not available here.

Share

COinS