In the 1950s bird migration information was sketchy without a good format. Most banding research was done with metal tags as leg bands on waterfowl. Not much information was useful. The leg bands counted birds killed in the field by hunters. Passerine research was provided by field birders who knew the flight songs of Swainsons’s thrush and other more common night migrants. On full moon nights spotting scopes were used to count birds passing through more reflective light arcs.

Mist nets and aluminum bands were used on smaller birds. The problem then is to mist net and equip these birds with transmitters. Today digitized transmitters are used, reducing the size and weight of transmitters. By 1970 radio transmitters weighed only one-third of an ounce. Now tags with microchips are less than two grams and are mounted on a bird’s back.

Often transmitters are solar powered and tied into satellites. Birds are located by GPS, but four to five ground sites are needed for a good fix.

To get tagged, birds are usually captured in mist nets, weighed and feathers taken along with blood samples. All information is digitized. The tags are geolocators, some even have microphones and soundtracks. Information is retrieved at ground stations.

Feather samples are taken to locate where nesting occurred. These are analyzed for DNA to produce a profile of the bird’s movements over time. Warblers have faced the greatest challenge in North America. Due to the five major ice movements over a wide area, over many major movements, warblers had to adjust their routes of travel and nesting areas and eventually turned into separate species.

Old feathers from early museum collections can also be used, helping to develop migration trends over the years.

A feather library is developing. Migration routes of small birds have changed with each of five ice age changes in North America. DNA changes in migration can be traced over the years. This information is processed by Genoscope, a genome sequencing research center, to map improvements.

Your atoms can be traced in the lab through stable isotopes analysis locating where you have been and what you ate over time. Geolocators are more commonplace for use on birds. They are used on uncommon warblers using feathers as locators. As to where the bird goes and what it eats, they also use stable isotopes.

This includes research on deuterium, a water particle molecule signature that is very scarce. This molecule may be eaten by animals and tracked years later. It becomes a locater after it is ingested. It is traced in the lab through stable isotopes analysis indicating where it was found. This locator can also be used on bats, reptiles and insects.

Deuterium is used extensively in North America research. In the environment it begins to fade in the soil as it moves north into Canada. Soil deposits in North America define regions allowing for dating of material a bird has eaten.