The most extreme example I've come across
No interactions present.
I wonder how it feeds with a beak like that. Perhaps with just eating softer, looser foods (for example, NOT peanuts)?
Significantly, it was near a very busy feeding station, but did not go anywhere near it. Instead it preferred to hop around some picnic tables where it was presumably picking crumbs. If only its huge mandibles were straight, then it could reach those peanuts other tits couldn't!
Deformed bills like these seem to be seen fairly regularly and the birds can reach adulthood so presumably can feed well enough. Many records are from garden feeders but whether that's because the birds need the supplementary feeding or because that's where people are to see them I don't know (maybe both). Indicentally, there's been quite a bit of research into the causes of this (work done on chickadees in Alaska) i.e. whether it's due to contaminants such as selenium and various organic pollutants. Interestingly, birds with deformed beaks not only showed reduced breeding success (which might be expected due to difficulty in finding food for chicks), but also aberrant incubation behaviour. Anyhow, if you are interested and fancy a longish read, the paper is at www.fws.gov/contaminants/OtherDocuments/Handel_et_al_2006_final_report_s...
I understand that when a bill overgrows like this the end eventually breaks off and a more normal bill is restored.
I got sent a photo at work of a Great Tit with only an upper mandible, which had grown so long and thin it looked like a Treecreeper's. Normally the two mandibles keep each other in check, but if one is lost, the other tends to grow. This bird was seen at a feeder behaving normally. I asked the sender to submit it to iSpot so hopefully the photo will turn up.
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Lat/Lng: 50.6, -2.1
OS grid ref: SY9787