Breeding Codes

(O) Species observed in a block during its breeding season, but no evidence of breeding. Use this code for species not in suitable nesting habitat. This code could apply to vultures or raptors flying over, herons or egrets foraging with no indication of a rookery, or ducks summering on an urban pond.

(X) Species encountered in suitable nesting habitat during its breeding season, such as a Virginia Rail in a marsh or Scarlet Tanager feeding in an oak woodlot in June. Also use this code for a male singing in a likely nesting area on only one occasion. If heard on a second trip in the same place, it may qualify as Probable (S).

(M) Multiple singing or territorial birds of a species detected within block on one day. This code is the lowest level of evidence that a species is probably nesting in the block. Seven singing individuals is an appropriate level of abundance. Most species listed as (M) can be upgraded to (S) during a later visit.

(S) Singing male present at same location on at least two occasions 7 or more days apart. This behavior presumes a permanent territory.

(P) Pair observed in suitable nesting habitat during the breeding season. This code is used when it is fairly certain that a mated pair of birds has been observed.

(T) Permanent Territory presumed through defense of breeding territory by fighting or chasing individuals of same species. Because territoriality involves the defense of a fixed area, it is useful to map locations of individuals to determine if they are singing or defending the same general area when surveying the block a week or more later.

(C) Courtship behavior or copulation between a male and female. Courtship behavior includes transfer of food, displays, and grooming between a pair of birds.

(N) This code applies when a bird is observed visiting the same likely nest site repeatedly, but which provides insufficient behavior for upgrading to Confirmed. This is especially useful for cavity nesters or for a shrub-nesting species that flies into the same thicket and disappears on several occasions.

(A) Agitated behavior or anxiety calls from adults usually indicate a nest site or young in the vicinity. This does not include agitation induced by "spishing", predators, or using taped calls.

(B) Nest building by wrens or excavation of cavities by woodpeckers. Wrens may build "dummy" nests before the female selects a nest. Woodpeckers will drill holes for roosting.

(PE) Physiological Evidence of breeding based on bird in the hand. This code is used primarily by bird banders and includes such evidences as a highly vascularized swollen incubation (brood) patch or an egg in the oviduct.

(CN) Bird seen carrying nesting material such as sticks, grass, mud, cobwebs, etc.

(NB) Nest building seen at the actual nest site, excluding wrens and woodpeckers.

(DD) Distraction Displays, defense of unknown nest or young, or injury feigning. Killdeers may give a "broken wing" act, a Cooper's Hawk may dive at you near the nest site, or an Ovenbird may run about with wings fluttering. A good way to differentiate between (A) and (DD) is to remember that when an adult performs a distraction display, it puts its own life in danger.

(UN) Used nest or eggshells found. Unless carefully identified, use this only for unmistakable eggshells and nests that were used during the Atlas period. If identification is unsure, forget it. Do not collect a nest.

(ON) Occupied nest indicated by adult entering or leaving nest site in circumstances indicating an occupied nest, including those in high trees, cliffs, cavities, and chimneys where the contents of the nest and incubating or brooding adult cannot be seen.

(FL) Recently fledged young or downy young. This includes dependent young only. Be cautious of species that range widely soon after fledging. One of the best features to look for is the length of the tail feathers. If shorter than the adults, the young probably originated locally. Young cowbirds begging for food confirm both the cowbird and the host species. Please make a note in the "comments" area of the Field Card when the host species is confirmed on the basis of only cowbird eggs or fledglings.

(FY) Adult bird carrying food for young or feeding recently fledged young. Use this code with caution. Some adults carry food a long distance or may be engaged in courtship feeding. Others such as the Common Grackle or Blue Jay may carry food away to consume it themselves. One of the best signs to look for is the repeated carrying of food in the same direction.

(FS) Adult bird seen carrying fecal sac. Many passerine adults keep their nests clean by carrying membranous, white fecal sacs away from the nest.

(NE) Nest with eggs or eggshells on ground. Nest and eggs must be accurately identified. If a cowbird is found in nest, use (NE) code for both the cowbird and the host species. Be careful not to disturb the vicinity of the nest.

(NY) Nest with young seen or heard. Take care not to cause premature flushing of nestlings from nest. Presence of cowbird young confirms both the cowbird and the host species.

Examples of Breeding Code Use

The following are examples of situations that may be encountered during atlasing to serve as guidelines in assigning breeding codes.

  • Immature loons, cormorants, gulls, or waterfowl (or cripples) summering on lake without suitable breeding habitat: Species Observed (O).
  • Common Loon, cormorants, or ducks in adult plumage summering on a lake with suitable breeding habitat, but no display or broods: Possible (X).
  • Herons or egrets (colonially nesting species) observed in marshes or along waterways away from nesting colony: Observed (O).
  • Green Heron or bitterns (non-colonial nesting species) observed in appropriate nesting habitat: Possible, Probable, or Confirmed, depending on breeding evidence obtained.
  • Black-crowned Night-Heron in subadult plumage during early summer: Observed (O).
  • Woodcock or Common Snipe nuptial flights and Ruffed Grouse heard drumming: Possible (X) if seen or heard only once (after departure of transient birds) Probable (S) if seen or heard 7 or more days apart at that location Probable (C) if courtship and display to female observed.
  • Shorebirds that normally breed in tundra areas summering in marshes or on a mud flat: Observed (O).
  • Rails heard in a marsh early in breeding season but not relocated on subsequent visits: Possible (X) because of their elusive nature.
  • Gulls frequenting dumps, plowed fields, lawns, etc. throughout the summer in unsuitable breeding habitat: Observed (O).
  • Woodpeckers drumming: Possible (X) if heard in breeding season Probable (S) if heard a week or more apart in same location in breeding season. Note: only Pileated Woodpeckers and Yellow-bellied Sapsuckers can be reliably identified by their drumming sound.
  • An unmated female bird builds a nest and lays eggs, but no male is ever seen or heard, and the eggs do not hatch: Probable (B). Generally, a nest with eggs would be Confirmed (NE), but in this instance, evidence would force a downgrading.
  • Killdeer doing broken-wing distraction display along roadside but young not seen; Confirmed (DD).
  • Male and female Scarlet Tanager observed together several times in same area but no nest ever seen: Probable (P).
  • Male House Wren sings all summer and stuffs nesting boxes with sticks but no evidence of a mate or fledglings: Possible (X).
  • Song Sparrow seen carrying nesting material: Confirmed (CN).
  • Wood Thrush seen on nest for an extended period of time but nest too high to see contents: Confirmed (ON).
  • Lark Sparrow observed once in late May in abandoned field: Possible (X).
  • Normal winter or typical spring migrants lingering beyond normal departure dates but no breeding evidence observed: Observed (O).
  • Second year male American Redstart singing abnormal song in hedgerow in early June: Possible (X).
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