The Massachusetts Breeding Bird Atlas 2 will use the following codes for describing bird behavior. It is worthwhile to study the codes and know them well – this is what you are looking for in the field. Breeding birds are often short on time, and careful observation of an actively nesting bird will usually uncover one of these behaviors. Remember to try to upgrade a species code, and pay attention to the Safe Dates. Breeding Codes are listed below and you can download
full breeding codes (PDF 27KB), or abbreviated breeding codes (PDF 66KB).
| OBSERVED: (all observations must be within Safe Dates) |
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| O |
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Species known to breed in Mass, but seen "passing through" (e.g. vultures, gulls), or a colonial species observed with no colony found in block, or a bird seen in unsuitable nesting habitat. Only use this code when no further evidence of breeding is uncovered. Work to upgrade these species if you suspect they are breeding in the block! |
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| POSSIBLE: (all observations must be within Safe Dates) |
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| X |
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Male or female seen or heard in suitable nesting habitat but no further evidence of breeding is uncovered. This includes a single drumming woodpecker, although the species must be seen to ID the woodpecker. |
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| PROBABLE: (all observations must be within Safe Dates) |
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| P |
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A pair (male and female together) seen in suitable nesting habitat. |
| S |
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Permanent territory presumed through song, heard at same location on at least two occasions, 7 days (or more) apart. This code can be used for drumming woodpeckers – although the species must be seen to ID the woodpecker. Both observations must be within Safe Dates. |
| T |
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Permanent territory presumed through defense of territory (often one male chasing another). This is a tricky code to use, and if the bird is watched longer, you'll probably find better evidence. |
| A |
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Agitated behavior or anxiety calls from adult. These calls are frequently directed at cats or snakes. Don't use this code if the bird is responding to "pishing". If the call is directed at you, back off. Much like "T" code, watch for better evidence. |
| C |
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(NEW: OK to use outside of the Safe Dates, except for ducks) Courtship behavior seen. Some species have courtship feeding rituals (e.g. cuckoos), some raptors have spectacular courtship displays (Broad-winged and Red-tailed Hawks, falcons), and this is one of the best codes to use for hummingirds. Consult "The Birder's Handbook" for succinct display descriptions. |
| N |
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Visiting probable nest site. Do not approach nests to check contents! Some nests are too high (e.g. the tops of trees) or enclosed (e.g. chimneys) for the contents to be seen. Listen for calls of begging young and watch for food deliveries to upgrade to Confirmed. If neither is seen or heard, the birds may still be on eggs – return a few days later if you can. |
| B |
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Building a nest by a wren, or excavation of holes by woodpeckers. Wrens often build "dummy" nests – a series of nests of which none may be used. Woodpeckers will excavate roost holes as well as nest holes. Don't despair – finding a wren nest means you are very close to a Confirmation. It is usually easy to Confirm wrens with CF, and woodpeckers with CF or NY. |
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| CONFIRMED: (can be use at any time) |
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| ON |
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Occupied nest: adult seen sitting on nest and likely incubating eggs or brooding hatchlings. No eggs or young seen. |
| CN |
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Carrying nesting material, such as sticks, grass, bark, etc. Don't use for wrens, crows, Monk Parakeet, or for colonial species for which you never find a colony (e.g. Great Blue Heron). |
| NB |
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Nest building at the actual nest-site. Don't use for wrens – attempt to upgrade wrens with CF or by the noisy NY. Don't use for Monk Parakeet. |
| PE |
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Physiological evidence of breeding (e.g. highly vascularized brood patch or egg in oviduct, based on bird in hand.). To be used by bird banders. |
| DD |
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Distraction display or injury feigning. Look for this in Killdeer and in many other species – other shorebirds, rails, some ducks, some warblers. |
| UN |
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Used nest or eggshells found. Caution: these must be carefully identified if they are to be accepted. |
| PY |
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Precocial young. Flightless young of precocial species restricted to the natal area by dependence on adults or limited mobility. |
| FL |
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Recently fledged young (either precocial or altricial) incapable of sustained flight, restricted to natal area by dependence on adults or limited mobility. |
| CF |
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Carrying food: adult carrying food for the young. Don't use for crows, Common Raven, raptors, gulls or terns unless you see them go into a nest site. |
| FY |
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Adult feeding recently fledged young. Adults feeding Brown-headed Cowbird young confirms both the host species and the cowbird. |
| FS |
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Adult carrying fecal sac. Fecal sacs, white membranous pellets excreted by the young, are usually carried from the nest then dropped. Occasionally birds drop them in the same place, and they form a spattered whitewash on cars, pavement, decks etc. |
| NE |
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Nest with egg(s). Do not approach nests to check contents! If you have the time to watch a bird through binoculars or with a scope, watch as the incubating bird turns the eggs in the nest. Many birds remove eggshells, and you'll find them on the ground sometimes – they can be difficult to identify! Nests containing Brown-headed Cowbird eggs confirms both the host species and the cowbird. |
| NY |
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Nest with young seen or heard. Frequently used code – young are usually noisy when parents return with food. Learn the sounds of begging young birds, and let that direct you to the general area of the nest where you can identify the parents. |
