That's great info.
They could have a weight at release anywhere between 110 - 180 grams. Perhaps the heavier birds would be chosen. So I have heard a device that is 5% a birds body weight is the limit.
They are captive bred birds. The intention is to hold the birds over the winter and then release this spring 2022 with trackers.
There are two scenarios.
1. They may not migrate.
If they have been here all winter they may not migrate at all and become a resident population.
A tracker that only did a few miles would suffice. To see where they may nest or if they are predated etc.
2. Come the Autumn they will migrate south.
This data would be better and show that what we are doing (helping the population increase) is working and birds are either coming back or staying resident.
The 5000 km posible migration journey either way could take between 20 to 40 days to complete. The data will tell us which route they take on migration, where they winter and if they rerurn to same breeding grounds.