Nature Notes: A murder most fowl
Last winter, I was headed home from work late one evening. I parked my car outside my Northeast Minneapolis apartment, and as I stepped out onto the sidewalk I could sense something odd. It felt like I was being watched.
Soon enough, I heard a rustling of wings in the trees above and looked up to see that I was indeed being watched – not by a single pair of eyes, but thousands! Thousands of crows had come to roost in the large ash, basswood and cottonwood trees near my home. I was astounded by the sheer number of dark figures perched among the branches.
Many Twin Cities residents have similarly experienced the yearly winter influx of crows. Groups of crows (known as ‘murders’) have frequented neighborhoods in north and northeast Minneapolis, south Minneapolis, and Elliot Park (featured in the video above), among other places, returning night after night and sometimes numbering in the tens of thousands. There’s even a facebook page celebrating the “Minneapolis Mega-Murder.”
But why are these birds gathering in such high densities in urban areas? There are a number of possible reasons. Some posit that the birds come to the cities for food. While the ground is frozen and crop fields are covered in snow, sustenance is more difficult to come by in rural areas, and the plentiful trash and scraps left in urban and suburban areas likely offer an easy meal.
Others propose that the urban heat island effect created by the cities attracts these and other species. However, this still doesn’t explain why they roost together in such large numbers.
Strength in numbers
The best explanation for this behavior is that like many animals, crows are safer together than they are alone.
During the growing season, crows can "roost easy" in rural areas, hidden in the safety of leafy branches. However, during the winter, the lack of leaves exposes crows to predators – most notably great horned owls. A single crow roosting on a branch is easy prey for an owl, especially given that crows have relatively poor night-vision. By roosting in large groups, the crows gain a measure of protection – and not just from an odds standpoint. While that same single crow is less likely to be picked off by the owl in a large group, the murder of crows can also alert each other to impending dangers.
Finally, crows may also use their time in the murder as an opportunity to communicate about food sources and find potential mates.
But while they’re not concerned about the spectacle they create, some residents are. Aside from the cacophony of cawing (“cawcophony”?) they make while they’re settling in for the night, some folks are simply unnerved by the massive groups of birds. Ultimately, it can be an awe-inspiring experience to see thousands of birds silhouetted against the night sky. Just don’t stand (or park) under the tree.