Steve Jones identifies a red-tail hawk through his scope during an early morning winter raptor monitoring session in February. Erica, a volunteer in training, records the bird on the official count.
For close to forty years Jones, along with a team of volunteers, has monitored the number of raptors that flock to Boulder during the winter. Once a month in the winter season, the raptor monitoring team drives along six survey routes and records the number, species, and location of each raptor they come across.
Each year their data shows that grassland dependent species continue to decline, while raptors that are more generalist in nature, like great horned owls and red-tailed hawks, thrive, as more grasslands are lost to urban influences. Urban environments have launched Boulder's population of generalist raptors into overdrive.
A red-tailed hawk hunts among the front yard of homes just outside of Boulder Reservoir. As residential homes continue to fragment grasslands, only the more generalist raptors, like red-tailed, are able to adapt to the human-altered environment and outcompete grassland specialists. Two of Boulder's grassland raptors, the ferruginous and rough-legged hawk, have declined by 90 percent due to the combination of habitat loss and the rise of red-tailed hawk according to Jones.
In 1950 only one Great Horned Owl was spotted during the Boulder Christmas count according to Jones. Last winter the count was over 100.
Known as the “Tiger Owl,” this species is a voracious hunter and has the most diverse diet compared to any other bird of prey. That, paired with their ability to live in almost any habitat, makes them a force to be reckoned with in the wild.
Great horned owls are believed to have contributed to the near-extinction of burrowing owls and long-eared owls in Boulder County according to CPW officials.
As more moved into the area, they began to outcompete long-eared and burrowing owls in every way. Great horned owls infiltrated their ideal nesting locations, outcompeted them for food, and even began to predate on long-eared and burrowing owls.
Great horned owls are easily recognizable due to their brown and orange coloration as well as the two feather tufts, resembling horns, on the top of their head.
Over the past two decades, only six long-eared owl nesting sites have been recorded in Boulder according to BCAS.
“Long-eared owls went from what looked like our most abundant owls in the 1880s to being very rare now," said Jones. “They just couldn’t compete with an urban adapted predator like the great horned owl."
A red-tailed hawk perches on a telephone pole as a train rolls by outside of Boulder.
Boulder’s red-tailed hawk population has doubled since 1990, according to BCNA, most likely due to their generalist nature.
“The number of red-tailed hawks we recorded last year alone was mind-blowing,” said Sue Cass, the President of Boulder County Nature Center.
Worldwide red-tailed hawks do extremely well in urban landscapes, as city environments provide more high-quality habitat. Roads, freeways, and neighborhoods provide a number of dependable perch sites like buildings, utility poles, and powerlines, so much so that urban-adapted raptors nest on man-made structures more often than natural ones.
These taller structures also provide ideal look-out posts that help raptors spot prey, because, the higher they perch, the farther they are able to see. An abundance of perching locations also means that raptors will use less energy when catching a meal. Rather than soaring at a high distance until prey is spotted, tall structures essentially do the work for them.
The city itself also provides a reliable and constant source of food for raptors.
Red-tailed hawks are frequently found on top of telephone pole as they provide stable places to perch and look for food.
Large amounts of small birds and mammals, especially rodents, live in almost every corner of a city, guaranteeing an abundance of food for raptors no matter where they reside. Also, the small birds and mammals that live in cities are slower and fatter than those that live in the wild, making city prey a much easier target.
"I've seen falcons hunting at puddles near the car wash because there are just so many rock dove pigeons there," said Jones. "It makes it almost impossible for the falcon to fail at catching one, so why wouldn't they want to hunt there."
European collared doves have invaded Colorado, especially within the Denver metro area, so much so that their population has increased by 200 percent since 2004 according to Cornell Lab of Ornithology. These small doves are extremely easy to catch and provide a hearty meal to so many raptor species.
More cars on roads and freeways result in an increase in roadkill, another meal that essentially requires no effort whatsoever from raptors.
A red-tailed hawks hunts for prairie dogs in a small strip of grassland that sits between the highway and a parking lot in Boulder.
American Kestrels are now more commonly found in urban environments than their native ones. Backyard bird feeders are to blame.
Relative to their body size, American Kestrels have a very large brain. Scientists believe that this may have helped the species realize that prey is much easier to catch around a birder feeder than out in the wild.
“Backyard bird feeders are the fast-food equivalent for urban adapted raptors,” said Cass.
An American kestrel perches on telephone wires. An urban adapated raptor, more kestrels are now found in city environments than in the wild.
Bird feeders attract large numbers of small birds and mammals in an extremely concentrated area all at the same time. This creates ideal hunting grounds as there is an abundance of food that is much easier to catch than it would be in a more wild setting.
More than 40 percent of households in the U.S. have one in their backyards according to Project FeederWatch, a citizen science project that allows participants to count and record the birds visiting their backyard bird feeders.
Since 1987 scientists have tracked long-term trends in winter bird distribution and abundance through more than 20,000 submissions on Project FeederWatch. Data has shown that most raptor species that frequent urban environments have started to use backyard feeders as a hunting ground.
By 2060 urban areas in the U.S. are projected to cover close to nine percent of the county, and as more humans flock to the cities, the number of urban adapted raptors is only projected to grow. But moving and adapting to urban environments is a catch-22 for raptors.
Although they thrive on the abundance of food and habitat within the city, urban adapted raptors are much more prone to injury. Local raptor rehabilitation centers have reported an alarming increase in admitted raptor in recent years, and attribute this growth to the hazards that come with living among humans.