Tagging of monarchs in New Zealand began in 2005-06 as a trial. From 2007 widespread tagging took place. Each tag had a discrete “code number” prefixed by two or three letters which related to a particular year (e.g. T series = 2020)
When participants ordered tags, their postal details were recorded on the tagging database online. As they released their butterflies, they would enter other information such as the weather, time of day etc. When a tagged butterfly was recovered, the person would enter the number from the tag there along with the postal location of where it was recovered, a description of the site and other important information as to weather etc.
The tagging programme was established to determine any migration patterns within the NZ monarch population. Based on the analysed data there appeared to be no pattern of migration or any common destination. Most recoveries were made within the general area in which they were released.
Anecdotal records, plus the tagging data, indicated that most monarchs overwintered in the area around where they eclosed.
Future investigation could be to identify the overwintering sites (some are already known) and having volunteers living in the vicinity monitor the populations. It is assumed that these populations go into diapause. A methodology could be established to enable those population counts to be undertaken. There could be observations made of flight patterns on warm, sunny winter days and any evidence of mating behaviour. This could be backed up with monitoring of swan plants for evidence of eggs and establishing whether they are fertile.