At one point the speaker pointed out that the hawk was checking out the few gulls flying by. And then people began noticing there were a lot more gulls. And then a couple dove at the hawk - breaking their dive still pretty well above it.
At this point, I figured the still picture didn't cut it and I switched to video. It starts out with a very brief shot of the woman holding the hawk, then goes up to the sky where we see and hear the gulls swarming about and making lots of noise - presumably a danger call, that a predator is in the area.
Then we go back to the platform as the speaker decides it's a good idea to put the red tailed hawk back into her carrying case, and then back up to the gulls (which is the thumbnail that's on the video.)
The representative of the library explained that normally these sorts of demonstrations take place indoors, but due to the renovations, the Marsden Auditorium wasn't available. Actually, this made for a much more natural and interesting lesson in bird behavior.
Here's an overview of a Stanford study on gull-predator behavior:
"When a weasel, fox, or other predator enters a breeding colony of gulls, numerous birds gather in the air above the intruder, making it very conspicuous. Gulls come from a considerable distance and circle or hover over the predator for quite a while, sometimes even landing in its vicinity before returning to their territories. With the exception of those whose nests are immediately threatened, the gulls show little inclination to attack. Instead they appear nervous and ready to flee.
Experiments using models of predators show that breeding Herring and Lesser Black-backed Gulls are more attracted to models that have a dead gull placed close to them than they are to the models alone. Furthermore, once gulls have seen a predator model with a dead gull, they are more attracted to it if experimenters place it within the colony again on the same day, even without the dead gull. Indeed, there is some evidence that the heightened reaction to the predator lasts at least a day after it is seen with the dead bird. This heightened reaction is specific to the predator model seen with the corpse -- there is no increased reaction to a model of a different predator subsequently presented in the same place. After seeing a predator model with a dead gull, the live gulls alight farther from the model on subsequent encounters. They remain attracted, but are more cautious.
These results indicate that the attraction of the gulls to their enemies is a method of learning about them. Apparently they can generalize -- they draw conclusions about the predator after another gull has had a lethal encounter with it. This is a beneficial reaction, since mammalian predators such as weasels and foxes may engage in "surplus killing -- dispatching more victims than they can consume. Also these hunters can specialize for a period of time on one group of prey. An animal that has killed one gull may be more likely to kill others; individual foxes have been observed habitually killing gulls in breeding colonies. It requires little imagination, then, to see the potential adaptive advantage for gulls of investigating predators."
And here's a view of the front of the library as of June 1, 2016. You can see some March 23 and May 11 pictures here.