Keeeeah, keeeeah, keeeeah. Grabbing my Nikon SLR, I stopped and looked across the fields. There, on top of a nearly leafless tree sat a solitary hawk on a branch about 20 feet up. I could not see him very well and so I looked through my camera, zoomed in and focused. Through my viewfinder I could see a gorgeous creature with speckled dark brown and white wings, a lightly patterned white and orange-tan breast, and a black and white striped tail. He turned his head to subtly eye the runners taking their morning jogs on the outer loop. After sitting for a few minutes he flew off towards the north part of campus, his red-shouldered wings flames against the light sky. What a beautiful, painted bird – truly a work of art. As I walked closer to the trees something caught my eye – a hawk feather. I picked it up and started heading back the way I came.
While walking back I wondered what this bird could be doing at Rice University, a tree-strewn campus but nonetheless a campus inside one of America’s largest cities. As I searched Web of Science for some articles about Buteo lineatus, more commonly known as the red-shouldered hawk, I found that many of the studies were done in Ohio by the same scientist, Cheryl Dykstra, and her team. Outside of school, Northern Ohio has been my home for the past 8 years – I have seen many red-tailed hawks (one actually hunts in my backyard) but I have yet to see a red-shouldered hawk in the buckeye state. I wonder what kinds of areas I would have to hang around to be able to see one back home. What do red-shouldered hawks look for in habitats and chosen nesting sites? Are these different across states? Why has this particular one chosen to live in the hustle and bustle of the area around Rice University, situated in Houston?
A study by Strobel and Boal published in the Wilson Journal of Ornithology compared regional variations in diets of breeding red-shouldered hawks and found that those that lived in northern regions of the United States preferred mammalian prey over amphibian, reptiles or invertebrates and vice versa for those hawks inhabiting southern states (graph from study can be seen below). Another study done in suburban southwest Ohio observed 21 nests for 256 hours to see what kinds of prey were brought back. It turns out that small mammals made up the largest percentage (31.5%), followed by reptiles (22.7%), invertebrates (18.8%), amphibians (17.7%), other birds (6.9%), and finally fish (2.5%). This just goes to show how diverse the hawks’ diets are – I suppose anything really goes, especially the nice, fat squirrels that tend to swarm Rice’s campus or the slow pigeons that strut around the ponds at Hermann Park.
It would be interesting to see how the homes and foraging territories that red-shouldered hawks picked and used vary across different states. I found a set of four studies dealing with home ranges and habitat selection of the red-shouldered hawk, each one done in a different state (Southern California, Southwestern Ohio, Georgia, and Northern New Jersey). For the study done in Georgia, they radio tracked five male and two female red-shouldered hawks between the 14th of April and the 22nd of August. Monitoring periods ranged from 59 to 102 days (average 88), totaling 656 hours of continuous observation. They found that forested habitats comprised 91% of the hawks’ home ranges. Of the forested habitats, bottomland (32.1%) and upland (21.4%) hardwoods were the most common. Stands of old sawtimber, regeneration, and pulpwood/sawtimber represented 19.6%, 16.3%, and 2.2% of home ranges, respectively. The non-forested habitats, pasture (4.5%) and clearcut (3.9%), were relatively rare in hawk home ranges. In addition, results from the NJ study by Bosakowski et al. stated that wetlands, stream bottomlands, small forest openings due to wetlands, and mixed forest habitats were preferred, while suburban and open water habitats were altogether avoided. 13 nests of the 12 they observed had no houses within the 300-m radius circles
The study done in Ohio by Dykstra et al. specifically concluded that red-shouldered hawks tended to use areas on the banks of rivers and streams, also known as riparian zones, and pond edges more than expected. Four of five birds they observed used wet areas in greater proportion than availability, and all birds used suburban habitats less than (n = 3 birds) availability. Rice University is not exactly pond central and the area around us is very suburban. However, Hermann Park has a huge pond and it’s only a flip flap of a wing away! Besides this, Bloom et al. in California found that four of the 18 hawks they banded and observed “showed a high degree of adaptability to human-altered habitats and human disturbance.” Looks like we have ourselves a unique city hawk! He came, he saw, he adapted! Or maybe he just thought those squirrels looked too delicious to pass up.
The last two articles I read looked at habitat selection and productivity of red-shouldered hawk’s nests. Does a certain type of environment allow for better success in raising young? Both of these studies, one done in central California and the other in southern Ohio, surprisingly found that reproductive success for nests in suburban environments were as successive as those in rural settings. In California they discovered that some trees supporting unsuccessful nests were located as little as 2 m from a building and 1 m from the nearest road. In Ohio, they looked at 48 active nests in a forested area near streams and 39 active nests in suburban development surrounding the city of Cincinnati, Ohio. They found that the success rates of both sites were very similar: 55%-63% in suburbia and 66%-67% in the forests. This can let us come to two conclusions: 1) that reproductive success is not affected by degree of urbanization and, 2) that red-shouldered hawks easily adapt to their environments. No wonder I was able to find one right here in the middle of Houston, albeit on a campus full of trees and right next to a large park with multiple ponds. Taking everything into consideration, we can assume these are truly versatile raptors.
In the end, I was not able to get pictures of those beautiful, flamed wings in motion – my maximum zoom was 100 mm. Not to mention the fact that I had a roll of black and white film in my camera. But who knows? Considering its adaptability, I might just hear a repeated “keeeah, keeeah” sometime in the very near future. And next time…I’ll be ready.
References (papers I used for my little research project)
– Looks into space (home range size) and habitat use patterns for adult red-shouldered hawks in southern California
– Compared macrohabitats of 14 red-shouldered hawk nest sites to 64 unused sites to reveal nesting location preferences
– Measured nest site selection and reproductive success of suburban-nesting red-shouldered hawks in southern Ohio and rural-nesting red-shouldered hawks in south-central Ohio
– Direct observations are used to quantify prey types, prey delivery rates, and adults and nestling behavior at nests of red-shouldered hawk s in suburban southwestern Ohio
– Measures the home ranges and habitat use of 11 red-shouldered hawks during the breeding season and 9 during the non-breeding season in suburban Ohio
– Studied home range and habitat use of red-shouldered hawks within a managed pine forest in the Georgia Piedmont during the breeding season of 1994
– Determined fledging success at nests of urban red-shouldered hawks in both native and exotic trees in central California
– Collected data on breeding season diet composition of red-shouldered hawks in south Texas and compared these data, and those reported from studies elsewhere to examine large scale spatial variation in prey use in eastern North America