Red-winged Blackbirds make the northwest corner of the park their party den and nursery in the spring. Then, around the Summer Solstice, the parents and their offspring take off and disappear to parts unknown. Now in late September, a number of them are back in the park. Not just a handful, but flocks of dozens. The males tend to perch on top of the bushes and flash their crimson epaulets and voice their mating call. And there are females present. But whether anything in the way of reproduction happens this time of year is doubtful. The main agenda item appears to be the fennel seed. Most of the fennel is done blooming. Some of the seeds are still green and tightly attached to their radial stems. Others are dark, and human fingers can collect a handful with a gentle pinch. For the birds, this is a cornucopia. Fennel seeds are rich in nutrients. Maybe these birds are building up their reserves for migration. Or maybe they’re just pigging out because it’s there and it’s easy pickings. Fennel is not a native plant, and not every human cherishes it. But like many immigrants, it’s become an integral part of the local ecology, providing services on which many legacy species, as well as other more recent arrivals, depend.