Basically low cut filters reduce or eliminate noise below the selected frequency. Filters can be good at reducing low frequency noise from mic handling and wind.
Most birds vocalise well above 220hz, so the choice of filter will not directly impact the bird recording - that is unless you are trying to record something extremely unusual, such as a Southern Cassowary, which can produce very low frequency sounds.
The problem is that filters can create a slightly unnatural sounding recordings, with low frequency noise cut-out but higher frequency noise remaining. I would therefore suggest that you apply a filter when facing problems with unwanted noise - if you have the mic tripod mounted (so no handling noise) and there is little wind or other noise, then perhaps you can get away without a filter - the more low level frequency noise you are hearing during monitoring, the higher the value of filter you can try.
It is also worth mentioning that a low cut filter applied in the field (mics and recorders can both have inbuilt filters) cannot ever be undone. Alternatively, you can create a substantially similar effect in many sound software packages, by using noise gates or equalizer effects. By altering the levels post production, you have the ability to 'undo' applied effects or vary effects until you have the sound you are most happy with.
Regards
Jon Bryant