The cows come when you call them by name. It is true. Just like a dog. These two came because they were called and the rest stayed behind.
Animals are smarter than many people would think. You can do this with birds too. I have a Harris's hawk. It takes one or two months to teach/train a Harris's hawk to fly to your arm after calling. Some birds need more time. But it is possible with time, patience and consistency. It requires a systematic traning every day. At first I called her to my arm by whistling after I put food (meat) on my arm. Later she flied to my arm simply by whistling, without putting the food on it.
You hit the nail on the head. Time and patience. (and consistency) It comes more instinctively in some animals than others.
That is so cool that you have trained your Harris Hawk!
Happy Sunday!