Roost From Above!

Dec. 6, 2025 under mostly cloudy with glimmers of setting sun, wind SW 7MPH, 40F; sunset time 4:45PM

While visiting from Boston and preparing for a local talk and walk on the North Bethesda winter crow roost, I made a deliberate effort to slow down and spend real time with the roost itself, not just at dusk, but across the full arc of the night and into early morning departure. Over the course of roughly twelve hours, I made four separate visits, starting out along Marinelli Road, then working my way south along Citadel Avenue, behind multiple buildings while walking east on Nicholson Lane, and finally looping north through the plaza areas off Rockville Pike. Each visit offered a different vantage point and observational purpose, allowing for careful cross-checking of movements, settlement patterns, and numbers rather than relying on any single moment or method.

First visit: early arrivals and staging (4:30 PM)

Beginning at approximately 4:30 PM, I walked down Marinelli Road, climbed to the top level of the nearby parking garage for an elevated view and time with a local group, then looped south along Citadel, west on Nicholson behind Jiffy Lube and Dr. Boyd’s veterinary facility, and around the perimeter of the NRC campus. This first visit focused on late final roosting and roost convergence activities with small and large groups moving in from local staging areas, directional flight lines beginning to organize, and early roost groupings as dark settled in.

At this stage, the roost footprint was still incomplete. Both species of Crows were clearly arriving and loudly vocalizing, but large numbers were still elsewhere, and the scene was dynamic rather than settled.

Second visit: peak convergence and flight bursts (8:10 PM)

Returning later in the evening under similar weather conditions, I repeated the same walking loop and rooftop vantage observations looking south. By this time, many more crows had converged into the roost area, as often happens, including birds arriving from more distant staging locations.

This time frame featured several dynamic flight bursts with concentrated waves of Crows bursting into flight blooms, circling the roost area and moving rapidly back into specific sections of the roost. These movements were visually striking but also underscored why flight streams alone are a challenging basis for reliable counting. Density changed rapidly, and movement was three-dimensional rather than confined to a single corridor.

Third visit: full settlement (10:30 PM)

The late-evening visit was critical. By 10:30 PM, the roost had largely settled, allowing for a very different kind of assessment. Using specialized low-light camera gear and night-vision binoculars with infrared imaging and external IR illumination, I was able to view the roost after nearly all birds were settled and  stationary.

At this point, I focused on:

  • identifying nearly all occupied roost trees

  • noting roost occupancy at multiple vertical levels, not just treetops

  • distinguishing smaller clusters from dense large clusters

  • mapping the full roost footprint perimeter  and later confirming habitat structure using Google Maps and aerial imagery

This phase provided the most stable foundation for counting Crows in the full roost

Fourth visit: morning departure (5:30 AM)

The final visit began before dawn and continued through the outbound morning flights, which occurred in multiple waves and directions rather than a single mass departure or single outbound flight direction. Observing departures helped confirm which sections of the roost were most heavily occupied and offered an additional cross-check against the overnight tree-based counts.

Counting approach: multiple methods, cross-checked

No single method was relied upon in isolation. Instead, I used:

  • tree-by-tree cluster estimates once birds were fully settled

  • individual counts in lightly occupied trees

  • group cluster counts in denser sections

  • rooftop vantage observations of localized flight bursts

  • careful review of all photographs taken

  • habitat verification using aerial imagery

  • comparisons across all four visits

Each estimate was made independently, then compared against the others. Where numbers diverged, I revisited assumptions rather than averaging blindly.

Final estimate and species composition

After cross-checking all four counts and reconciling differences, I arrived at a final, conservative estimate of approximately 11,500 crows perched in the roost trees on this night.

Equally important was species composition. A high proportion of Fish Crows was evident, mixed throughout the roost with American Crows. From prior conversations with local observers, there appears to have been no previous dedicated effort to:

  • conduct a full overnight count of this roost, or

  • explicitly recognize and account for it as a mixed-species winter roost

That alone makes this site especially interesting from both a behavioral and ecological perspective.

A note on numbers

Large winter crow roosts are dynamic systems. Numbers shift nightly with weather, food availability, disturbance, and seasonal timing. The value of this effort lies not in claiming precision, but in taking the time to apply multiple, well-established and time-tested observational approaches, acknowledge uncertainty, and resist the temptation to let dramatic moments drive inflated conclusions.

This roost clearly supports many thousands of crows, dominated by Fish Crows, and merits continued careful observation. Future counts, especially those possibly incorporating thermal imagery, will help refine our understanding of the size and scope of this roost.

For now, this overnight visit provided something equally valuable: a grounded and disciplined assessment of this remarkable winter gathering!