Winterthur Garden Blog

Jim Pirhalla, horticulturist for the Sundial Garden and the Pinetum writes: 

This year is the first year, at least that I am aware of, that a pair of hawks has nested in Winterthur’s Pinetum during the decade or so that it has been under my care; the particular breed of hawk being the Cooper’s hawk. The females of the species are slightly larger than the size of a crow whereas the males are slightly smaller than one. These hawks have long, streamline bodies and are quick fliers.  They closely resemble the sharp-shinned hawk but the Cooper’s is the larger of the two species. Most references that I’ve come across have noted that the Cooper’s is far less common than the sharp-shinned as well.

This spring while I was working in the Pinetum, I noticed the pair building their nest about 40’-50’ up in one of the tall conifers. I believe that the nest was originally built by a pair of crows last season and the hawks simply added some new nesting material on top, which is commonly done. One of the reasons that I think that this may be the first time that a pair of Cooper’s has nested in the Pinetum is that they were surprisingly noisy! During their nest building phase the female would loiter close by in a tree and whenever the male would arrive from hunting, they would greet one another with some squawking. The noise was somewhat of a cross between a chicken’s cluck and a duck’s quack with perhaps a touch of seagull thrown in for good measure. I also observed the hawks gathering nesting material from within the Pinetum itself, sometimes even from the tree next to it. Interestingly, the pair did not seem to mind people walking within their nesting territory, for they were not easily startled or disturbed.

Another observation that I made was the fact that a pair of common crows set up house keeping in another conifer not more than 50’ from the Cooper’s nest. Crows normally pester the larger hawk species but the Cooper’s are fast enough that they were the ones that kept the crows on their toes, so-to-speak. Whenever one of the crows would leave its nest, one of the hawks would be right on its tail, chasing it out of the Pinetum. I noticed that the nesting pair of crows successfully raised at least one offspring though I did find the remains of another youngster close by, presumably a nest mate. I also found the remains of an adult earlier in the spring, possibly last years offspring, which often remain with the breeding pair, acting as centurions as well as helping with feeding the young.  I don’t know if the hawks were responsible for their demise but it’s certainly feasible.

Although I would see or hear the hawks from time to time in the Pinetum, I was never quite sure how their family matters were progressing. As I mentioned before, the crows had one offspring, which had been out of the nest and flying around for a quite a while already but I had no clear indications if the hawks were successful in raising their offspring. It wasn’t until the first week in July when I saw a youngster out on the end of a branch in the nesting tree that I realized that they had raised at least one. The following week I noticed, in fact, three youngsters, all perched in one of our Blue Atlas Cedars. They all seemed to be staying within the Pinetum for the time being, even flying back to the nest on occasion. I suspect that soon they will be venturing further out for they are flying around pretty well at this point. It will be interesting to see if the mating pair returns in the years ahead to raise another family in the Pinetum!