In the article it states they banded the young eaglets. The band appear to be metal and they appear to be tight and permanent. My question is how does the band not constrict the leg of the eagle as it grows? I’ve seen adult eagles, their legs are pretty thick.
I am far from a bird banding expert, but the bands I have seen start out as a thin, flat metallic strip that is wrapped around the leg. The ends may overlap, but they are not glued or connected. As the bird grows, the wrap merely expands. I suppose if a leg really grew, the strip might fall off, so I imagine the length is chosen for the best outcome.
Not a wild bird, but on some of the veterinarian TV shows I’ve seen episodes where a parrot owner brings their bird in because the band put on by the breeder is too tight and restrictive.
It’s worth noting that Golden eagles reach adult size rapidly (Googling suggests around 9 weeks). I suspect there’s not much growth left to go when banding is done.
Again, not a bird banding/ringing expert, but there are different band types for different purposed- the ones mentioned by GaryM used on pet birds are usually solid rings; they’re intended to be part of the bird’s ID for its whole life, and evidence that the bird is captive bred. The bird may not be legal to sell if they don’t have one. These are solid so they can’t be removed, but this isn’t usually too big a problem; they’re put on young captive bred birds at the optimum time, and there’s someone there to keep an eye on them, in case of problems like getting a loose ring caught on stuff while the bird’s still growing, or the ring getting tight due to a leg problem or unexpected growth.
For wild birds, a non-joined ring is used, as part of projects recording population dynamics and migration and the like. This is partly because it’s obviously more risky for a wild bird to have a non-removable ring, if it gets caught on something or gets a swollen leg there’s no-one going to rescue it or take it to the vet to get it removed. There’s also less need for permanence; while those studying birds would obviously rather the ring stayed on for the whole course of the project, it’s not worth risking a bird’s life for. These can be fitted onto adult birds, which is good for studies, but useless as evidence of captive breeding or permanent ID.
Also of note, rivers bands are used on eagles, and as these are eagle chics that makes sense. I also imagine these people know what they are doing and have performed this many times. Possibly the depth of field in the pictures prevents an accurate depiction of how much room is left around the band.
Birds are typically close to adult size by the time they leave the nest. While I haven’t banded raptors myself, I expect they would have waited to band the chicks until just before fledging, and made any allowance for expected growth in determining the size of the band to use.