Judith Swan, of Dunedin, asks :-
We provide fat and seeds for birds over winter. Often in a group of silvereyes, there will be one bird that will sit on a branch near the food or on the feeder and ruffle its wings at the other birds as if to say "go away this is my food source!" We've also observed this bird sometimes fly at and chase other silvereyes away from the food. Sometimes they will also try the wing ruffling at Greenfinchs, who ignore it! What does this ruffling signify?
Laura Molles, a bird ecologist at Lincoln University, responded.
Wing fluttering is one of several signals in the silvereye’s aggressive arsenal. While it appears in different contexts (such as mating and begging), in this instance it’s meant to warn other silvereyes that they’re likely to be attacked if they come much closer. If the warning isn’t heeded, two silvereyes may end up stretched tall, beak-to-beak with gaping mouths, screaming at one another, or even in an all-out fight. Cute little birds can be ferocious!
Fortunately, it rarely comes to this. Within a flock of silvereyes, individuals almost certainly recognize one another (even though we can’t), and know where they sit in the pecking order. Who is dominant can depend on a variety of factors, including sex (males are generally dominant over females), age (juveniles are generally subordinate), testosterone levels and body condition. These characteristics may not be immediately obvious to new birds joining a flock, and they have to learn their place through experience.
Interestingly, it’s not all bad news for birds below the top tier. While the most dominant individuals may get first dibs on food, they can spend so much time and effort chasing others away that they don’t maintain their weight as well as those in the middle ranks. Birds at the bottom of the heap have to wait their turn, but don’t waste energy on constant squabbling. And subordinates don’t always miss out: the effects of the hierarchy will be most pronounced when access to food is limited, as it is at a small bird feeder. The flock’s rowdy behaviour can be instantly improved by dividing the food between multiple feeders. Even the most determined top-ranking bully can’t be in two places at once, and the end result may be that everyone, even the top bird, gets more to eat.