Crest calls
AS we get older, the general rule is that our hearing becomes less sensitive, especially to higher-pitched sounds. Given that they have remarkably high, thin calls and songs, Goldcrest and Firecrest are particularly likely to be overlooked in the soundscape of a large woodland. Recently, even breeding bird census data has been questioned because of a potential bias in older observers, as such birds may not be heard so well at a distance from the transect line.
Listen in conifer woods and oakwoods where columns of ivy go high into the canopy and there is a mix of old holly. The calls of these two can be more or less impossible to distinguish for sure, but there are some that may be distinctive. Goldcrests tend to have a three- or fournote call, like zree-zree-zree, or a harder, single note. The song is more distinctive, a high-pitched, rhythmic phrase with a slight terminal flourish, si-sissi si-sissi si-sissi sissi-siswee-it.
A singing Firecrest has a call of two or three notes, the first a little longer, like zee-zi-zi. However, it may be much like that of a Goldcrest. The song is a better bet: an accelerating trill, but without the repetitive rhythm or flourish of a Goldcrest: zi-zi-zizizizizizi.