Recording detection

Singing males are more detectable than females for many species

While the standard BBS counts are the main aim of the survey, as an optional extra volunteers who are interested in trying something new can record how birds were detected. 

The categories are Song, Call and Visual. This can help analysts to work out actual numbers of birds present, as there are differences in detectability between singing males, birds detected by call and birds seen. Read about how these estimates are used, or take a look at

from the 2012 BBS report.

The aim of this new recording is NOT to record evidence of breeding, or how a bird was identified, but to note how your attention was drawn to each bird.

It is important that you do not change the way you carry out the survey in order to collect this additional optional information.


Part of a field sheet with detection types marked


Field methods

•  Record the way you first detected the bird (or group). If a bird is detected by sight, but later starts to sing, record this as a visual detection.

•  Record your data on your field sheets by circling a singing bird, underlining a calling bird or leaving a record unmarked if you detected the bird visually. You can also use the codes S for song, C for call and V for visual.

•  While optional, if you choose to record detection type it should be recorded for ALL birds on a visit.

•  Take care not to spend more than a few seconds recording detection type. There is no need to record whether birds are male or female, since this could add significantly more time to the survey.


Recording detection, not method of identification

It's important to record how your attention was first drawn to a bird, not the method you used to identify it to species.

"I saw a small bird perched on a bush ahead of me but I couldn't identify it because of the angle of the light. When it started to sing I knew it was a Robin"

The bird in the example above should be recorded as detected by sight, not by song.


Defining songs and calls

Male and female woodpeckers can both drum,

so drums should be recorded as calls

The aim of the new methods is to record easy, obvious information, e.g. whether a Chaffinch was detected by song or sight. If you find any sounds very hard to define, just record them as call - detection information for 'non-obvious' species is unlikely to be used for analysis!

For the purposes of recording detection, a song is a sound normally made only by males, while a call is made by both sexes.

In general, sounds made by passerines (songbirds) are easily distinguished as songs or calls, while sounds made by non-passerines (including wildfowl, birds of prey and seabirds) are calls. However, there are many exceptions, and some of the most relevant to the BBS are mentioned below:

  • Non-passerine ‘songs’ that you may hear include the ‘crow’ of a Pheasant, cooing or purring of pigeons or doves, the ‘cuckoo’ of a male Cuckoo, displaying grouse, and display flights by breeding waders including Curlew, Lapwing, Dunlin and Redshank.
  • Most sounds made by corvids (crow family) are calls. Swift screams and Green Woodpecker ‘yaffles’ are calls. While the males of some ducks make different sounds to the females, these should be recorded as calls.
  • Non-vocal noises. Woodpigeons wing clattering and woodpeckers drumming should be recorded as calls, as with most other non-vocal noises. The exception is drumming Snipe, which should be recorded as detected by song.
  • Some songbirds have songs that are simple or rarely heard, e.g. Long-tailed Tit, Bullfinch, House Sparrow and Nuthatch.
  • If in doubt, consult a reference (e.g. Collins Bird Guide or Birds of the Western Palearctic) to see if the sound you heard is defined as call or song. The library of songs and calls at may also be useful. If still in doubt, record as call.
  •  may be of use.

*NEW Detection Type quiz!*

So far, this additional recording method has been very well received, with over 67% of squares recording how birds were first detected. A first look at the data collected so far was discussed in the 2014 BBS report. To get a feel for recording detection type, or to double check you are recording detection type correctly, please download the 

Submitting detection type records

Before you start inputting your data online you will need to specify whether you were recording detection type. If you answer 'yes' the system will require detection type for every bird record. If you answer 'no' you will not be able to start inputting detection type later. It is not possible to switch while entering data from a visit without deleting the whole visit and starting again.

You cannot submit detection type on paper forms. We recommend submitting data online, but if you can't, we may be able to arrange for someone to input your records online. Please speak to your RO. 

Online data entry



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