story identification - Paperback novel about a man who kills a birdlike alien on his balcony with a watering can

This is probably Kevin O'Donnell's ORA:CLE.

It takes place in a fairly far-future where global warming has forced the entire (surviving) population of earth into living completely indoors in large apartment/office towers. There are matter transporters that can only send non-living items (it kills living things). Some time after everyone moves into these towers the Earth is invaded by winged aliens called Dacs (short for pteradactyls). The Dacs don't seem to care about taking over in any usual sense, they just keep us from developing space travel and hunt us for sport - but only if we go outside.

Here's part of the scene with the watering-can and the winged alien:

    He moved. Whirling to his right, he swung the
watering-can like a tennis racket, wristing it up and into an overhead
backhand shot. He had plenty of time because time had slowed. A sub
broke water in New Haven harbor. The wrought-iron railing cast a
short, slanted shadow. The Dac mothership drifted three klicks
overhead. His lungs were already
laboring.
    To his right, great bat-wings
fluttered as the Dac tried to balance itself. The five-centimeter
claws of its knobbly eagle’s feet skidded slightly on the flagstones.
Its carrot-colored beak snapped in frustration, flashing razor-sharp
teeth and a predator’s hook to the upper jaw. Its huge head bounced on
its child-sized torso. Its hand—with a thumb, three fingers, and
retractable claws—wavered as it tried to aim the gun that gleamed like
silver.
    Ale had spun nearly a hundred and
eighty degrees. Thinking, But the damn alarm was guaranteed! he
hurled the watering-can.

After killing the alien, other aliens (of the same species) come to investigate and apparently decide that this was a "fair killing". The cut off the dead one's beak and give it to the main character as a trophy.