The following are codes that may be referred to on the website or in the biennial reports.
Ringing Schemes
Country codes are only shown if the bird was not ringed with a BTO ring.
| BLB | Belgium, Bruxelles |
| CIJ | Channel Islands, Jersey |
| DDH | Germany, Hiddensee |
| DEH | Germany, Hiddensee |
| DEW | Germany, Wilhelmshaven (Helgoland) |
| DFH | Germany, Wilhelmshaven (Helgoland) |
| DKC | Denmark, Copenhagen |
| ESI | Spain, Madrid |
| FRP | France, Paris |
| HES | Switzerland, Sempach |
| ISR | Iceland, Reykjavik |
| NAW | USA, Washington |
| NLA | the Netherlands, Arnhem |
| NOO | Norway, Zoological Museum (Oslo) |
| NOS | Norway, Stavanger |
| PLG | Poland, Gdansk |
| POL | Portugal, Lisbon |
| SFH | Finland, Helsinki |
| SVS | Sweden, Stockholm |
Age at ringing
| 1 | pullus (nestling or chick) |
| 2 | fully grown, year of hatching unknown |
| 3 | hatched during calendar year of ringing |
| 4 | hatched before caledar year of ringing, exact year unknown |
| 5 | hatched during previous calendar year |
| 6 | hatched before previous calendar year, exact year unknown |
| 7 | definitely hatched two calendar years before ringing |
| 8 | hatched more than two calendar years before year of ringing |
Condition at recovery
| X | pullus (nestling or chick) |
| XF | fully grown, year of hatching unknown |
| XL | hatched during calendar year of ringing |
| + | hatched before caledar year of ringing, exact year unknown |
| +F | hatched during previous calendar year |
| S | hatched before previous calendar year, exact year unknown |
| V | definitely hatched two calendar years before ringing |
| VV | hatched more than two calendar years before year of ringing |
| R | pullus (nestling or chick) |
| RR | pullus (nestling or chick) |
| // | pullus (nestling or chick) |