Abberant (?) Goldcrest

The 16th of march a friend invited Jesse and me to his birthday party in Geldrop, we could stay there and we were planning to go bird watching the day after on the Strabrechtse Heide (heather). After a nice party, it reminded me of parties before I went studying, we went off late to the heather, as Marijn had quite a hangover. It was clouded, but not cold at all and almost wind still. We decided to check the place where Marijn had found a Rustic Bunting two years ago. It was stuffed with birds and a good place to relax. My memory let me down for a moment when I heard a Firecrest (Regulus ignicapilla) calling. Jesse and Marijn weren't that sharp either, so we waited to be sure. Firecrests aren't that common in this part of the Netherlands, later we found out that this was the first sighting in two years for the Strabrechtse Heide (according to waarneming.nl). Two birds were present and the male was singing frequently. The call of Firecrest looks a bit like Goldcrest (Regulus regulus), but I would describe the call of the Firecrest as a high pitched sharp 'ti-ti-ti-ti' and that of the Goldcrest as a high pitched 'sri-sri-sri-sri', recognisable for the better listener. The song of Firecrest is also a high pitched 'ti-ti-ti-ti-ti', but raises slowly in pitch during the phrase. On the other hand, Goldcrest varies in pitch during the song phrase 'tí-tidelí-tidelí-tidelí-tidelilili' with a little 'r', but I will come back to that later in this post.
I made a decent recording of the singing Firecrest:


Back to the song of Goldcrest: on 18 january 2012, Bert Haamberg recorded a strange song of Goldcrest (recording can be found here). A lot of imitations and low pitched notes, amazing! Some other observers mentioned this kind of subsong as well, but never common. 14 march, Teus Luijendijk also put a recording on Xeno-canto of subsong of Goldcrest. The 17th of march, I recorded a Goldcrest which was also imitating other species (like Long-tailed Tit). It seams to be not that uncommon, but a few have paid attention to it. Proof that there is a lot to discover in the world of sounds!

Subsong Goldcrest by Teus Luijendijk:

Subsong Goldcrest by me: