Siskin conundrum

This pair of Siskins Carduelis spinus, arrived in our garden on the 3rd April and were seen together until the 13th April. Since then, and up until today, we have seen on a daily basis just a single Siskin. The male is the more yellower one with the black cap and the other one is presumably the female, or though it could be a juvenile as it is quite difficult to distinguish between the two. The single Siskin still visiting the feeders could be the female/juvenile above, or of course a totally different bird altogether.

Update - 3 seen on 18th May - they all look like juveniles.

2008 - 2 Siskins were seen on the 1st and 24th March, and a single one (female/juvenile) on the 12th and 25th March. 3 Siskins were seen on the 18th May (they all look like juveniles).
2007 - No Siskins recorded.
2006 - 2 Siskins were seen on the 16th April.
2005 - No Siskins recorded.
2004 - 1 Siskin on 28th Feb. 5 Siskins on 15th March.
2003 - 2 Siskins on 2nd Jan.
2002 - 2 Siskins on 24th Feb.

Siskins can be seen in the UK all the year round, as around 350,000 pairs breed here. During the winter we get migrants from Scandinavia and the continent coming over, but these don't necessarily return until late April or even early May. Therefore it is difficult to tell whether the Siskins in my garden are resident or migrants. If anyone has any ideas, then please leave a comment.