Great project! I have wanted to do something similar with my hummingbird feeder to determine what time of day the birds tend to visit most often.
You can piggy back on my object detection api - it can detect birds - just tried with the image => https://images.unsplash.com/photo-1520638023360-6def43369781...
Request example => https://pastebin.com/1Wnyb6PD