Ravens and hawks in the USA, new study

This video from the USA says about itself:

Raven’s nest with 6 eggs on window ledge of office building located in West Los Angeles.

From Wildlife Extra:

Raven populations rise in US as they turn man-made structures to their advantage

A new study by the Wildlife Conservation Society (WCS), US Geological Survey (USGS) and Idaho State University (ISU) has revealed how man-made structures affect the nesting of a variety of avian predators.

The study took place on the sagebrush landscapes of the US Department of Energy‘s Idaho site and surrounding areas in the state, locating nest sites for all four species over a three-year span.

Researchers compared common ravens, red-tailed hawks, Swainson’s hawks, and ferruginous hawks.

This video from the USA says about itself:

A family of wild Swainson’s Hawks (adults & juveniles) in the Sonoran Desert of Arizona encounter a lone coyote…

The Wildlife Extra article continues:

Overall, the analysis showed that energy transmission towers and other artificial substrates (e.g. mobile phone towers, billboards and buildings) are overwhelmingly preferred by ravens as nesting sites, and are not at all favoured by any of the three hawk species.

“Raven populations have increased precipitously in the past four decades in sagebrush ecosystems, largely as a result of fragmentation and development of anthropogenic structures,” said ecologist and study lead author Peter Coates.

“Our study shows that in addition to habitat fragmentation, the addition of human-made structures benefit ravens, whereas some species of raptors like the ferruginous hawk have been impacted and limited in nesting areas.”

Why the difference in nest selection between ravens and large hawks? The answer may be linked to the availability of preferred prey.

“Ravens are opportunistic foragers, eating just about anything, including carrion,” said co-author and USGS ecologist Kristy Howe.

“In addition, they tend to be highly intelligent birds that adapt quickly to changing environments and have been shown to transmit learned behaviours from one generation to the next.

“Conversely, hawks tend to be strongly territorial, intolerant of human disturbance, and prefer prey like jackrabbits that occupy similar habitats.”

Ravens were classed as an uncommon breeder within this area as recently as 1986. They are now the most pervasive predatory species nesting in this area, accounting for 46 per cent of nests among the four.

Transmission towers are the tallest objects in the study area. Nesting on or near them may afford ravens myriad advantages, including a wider range of vision, greater attack speed, and greater security from predators, range fires, and heat stress.

While this is good news for ravens, it could be bad news for sensitive prey species, including the greater sage-grouse.

Howe speculates on the study’s other implications and directions for future research: “Since ravens are important predators of young birds and eggs, and hawks are predominantly predators of adults, these landscape changes could shift ecosystem dynamics.

“Predation risk would now likely be greater for sage-grouse eggs and young, and correspondingly lower for adult sage-grouse and other prey species.

“This adds new insights for ecosystem managers who seek to understand the complex relationships between ravens, hawks, sage-grouse populations, and habitat changes.”

“Industrial development, wildfires, invasive plant species, and other disturbances are changing sagebrush landscapes throughout the western United States,” concluded Peter Coates.

“Our results shed light on how these avian predators might change with them.”