Canadian Atlas of Bird Banding

Explanation of Species Accounts

4.1 Species name

The first items in each account are the species' common and scientific names, for which we follow the seventh edition of the Check-list of North American Birds (American Ornithologists' Union 1998 and updates through the 50th supplement), and the species number from The North American Bird Banding Manual (Gustafson et al. 1997).

4.2 Encounter maps

The encounter map shows lines joining banding locations with encounter sites for birds encountered more than 100 km from the banding site. The symbol at the end of each line marks the encounter location.

Prior to mapping, data were screened to delete records showing encounters within 100 km of the banding site (the latter being relatively uninteresting for depiction on maps). Encounters with inexact location codes or coordinates were also excluded, except as follows. Records providing degrees of latitude and longitude but lacking the exact 10' block were assigned coordinates at the southeast corner of the 1o block. Some of the older encounters from Mexico report the state but do not give any coordinates; in such cases, we assigned coordinates for the centre of the state. To ensure that scarce longdistance encounters would be mapped, we also assigned coordinates for inexact locations within Central or South American countries, giving coordinates for the centre of the relevant country.

For species with few band encounters, every record of movement greater than 100 km could be mapped individually. However, this was not possible for species with high numbers of encounters, as even maps with as few as 50 lines can appear too cluttered. We therefore reduced the complexity of the maps using several methods. For example, for a few species (noted in the text), we omitted encounters within 200–400 km of the banding site, as opposed to the usual 100 km. A second approach was to produce several maps for a species to allow depiction of more cases.

Most commonly, we used a thinning process. First, groups of records were identified that shared the same banding and encounter coordinates (i.e., all the birds were banded within one 10' latitude-longitude block and encountered within another 10' block). Then a single line was plotted with a larger symbol to indicate the number of encounters represented by that line (see key on each map). If further thinning was required, coordinates were rounded to form larger degree blocks (instead of 10' blocks), and new (larger) groups of records were formed that shared the new banding and encounter coordinates. From each group, a single record was randomly chosen to represent the group on the map, and these lines were plotted using their original coordinates. Again, the size of the symbol at the end of the selected line shows the number of records represented. If the map was still too crowded, the process was repeated with larger block sizes until the maps became clear. Block size in degrees (in decimal format) is shown with each map for which block size was enlarged above 10' of latitude and longitude for the purposes of thinning.

The number of encounters represented by each symbol is consistent across all maps, with only two sets of frequency classes being used: one for large data sets (map symbols are triangles) and one for smaller data sets (map symbols are squares).

The result of the thinning process is a set of lines joining banding and encounter locations that summarizes geographic patterns of movement, rather than showing every encounter separately. The advantage of this system is that sparse or outlier records are not eliminated in the thinning process, whereas dense areas of repetitious records are rigorously weeded to reduce clutter. The disadvantage is that many individual records (sometimes hundreds) are not shown on the maps. When block size is large (over a few degrees), the text draws attention to that fact and notes any distortions of pattern that may result.

4.3 Narrative

Each narrative begins with a clarification of taxonomy if taxa traditionally recognized by banders do not coincide with those in current use by systematists. A short description of the North American breeding distribution and each species' wintering area follows, based mainly on Peterson (1980), the American Ornithologists’ Union (1998 and subsequent supplements), Godfrey (1986), and individual species accounts in the Birds of North America series (Gill and Poole 1991–2001).

The main body of the text discusses movement patterns revealed by the encounters and refers to specific records (by number) that are listed below the text. If there are major published analyses of band encounters for the species, relevant results are summarized briefly in the account, even if published later than the cut-off date for including band encounters (end of 1995). Cited longevity records (from the U.S. Banding Laboratory web site) were current as of 2006.

4.4 List of selected encounter records

The encounter records are listed in a standard format. Each one occupies two lines, the upper containing mostly the banding information, and the lower, the encounter details. The band number is given first. Below it, on the second line, appear either the initials of the bander or, if these cannot be traced, the bander’s permit number or acronym of the permitting organization or the name of the country of banding. (This is the only banding information that appears on the second line rather than the first.) The name of the bander can be displayed by scrolling over the bander’s initials.

All codes in the encounter listings are from The North American Bird Banding Manual (Gustafson et al. 1997). The meaning of the codes can be displayed by scrolling over the code. These codes are used in preference to the “international” symbols because they contain more information (Brewer and Salvadori 1978). Following the band number and the initials or permit number of the bander or country of banding are two sets of codes: on the upper line, the alphabetic versions of the codes for age (first) and sex (second) of the bird at banding; on the lower line, the numeric codes for “present status of bird and band” and “how obtained” from the encounter data. Together, the latter two codes give some indication of the completeness of information for the particular record.

Next are the dates of banding (above) and encounter (below). Note that these are in the order day/month/year (not month/day/year as they are in the computer files), to conform with common Canadian usage. Special codes indicate inexact dates of encounter (an explanation is provided by scrolling over the code).

Dates are followed by the names of the places of banding (above) and encounter (below). Most place names were obtained from the gazetteer of banding and encounter localities on file at the U.S. Bird Banding Laboratory. The location names in the gazetteer were assigned by Laboratory personnel and frequently differ from the names that banders assign to their own sites. We have changed site names to those more recognizable by banders in the few cases where we knew which names were more appropriate, but in many cases we were not able to do so. When locations were not given in the gazetteer, we used atlases to find nearby place names.

The next data in the encounter records are the latitude and longitude of banding (upper line) and encounter (lower line), expressed as the coordinates of the southeast corner of the appropriate 10′ geographic block (Gustafson et al. 1997). Question marks indicate inexact locations. Where we assigned coordinates (see notes in section 4.2), the distance travelled (see below) is given as approximate. In a few specific cases for which revelation of the breeding locations might be deleterious to the bird, precise banding locations have been omitted. In these cases, we have identified only the province or state and rounded the geographic coordinates and the distances travelled.

The last data given are not extracted from the standard computer files but have been calculated separately. On the upper line is the time elapsed between banding and encounter (omitted when date of actual encounter was ambiguous or the bird was long dead at the time it was found), and on the lower is the calculated distance and direction between banding and encounter locations (see Additional details on data coding and analyses). The latter is blank when locations are inexact or where approximate locations were assigned (see section 4.2), in which case approximate distance and direction were calculated. Most encounters listed in detail are specifically cited in the text, but often the bird with the longest period between banding and encounter is listed at the end without any comment.

4.5 Summary of banding statistics

A summary of banding statistics is provided for each species with bandings in Canada. Data are arranged in three columns: birds banded in their first calendar year of life (Hatch Year), those banded in their second or subsequent calendar year of life (After Hatch Year), and the total banded regardless of age (including birds of unknown age when banded). An explanation of each line in the summary table is given below.

No. of Canadian bandings (1955-1995):

Banding numbers were not handled by computer prior to 1955, so this item and the next ("No. encountered per 1000 banded") are restricted to the 1955–1995 period. These two lines are italicized in the table to emphasize that they are a restricted subset of the numbers appearing in the remainder of the table. The term Hatching Year refers to birds banded in the calendar year of hatching; After Hatch Year includes all older birds. Note that the Total also includes birds of unknown age.

No. encountered per 1000 banded (1955-1995):

((No. encounters of birds banded in Canada, 1955-1995) x 1000) / (Total no. banded in Canada, 1955-1995)

The number of encounters includes birds killed, found dead, or captured alive, as well as sight records (i.e., bands read from a distance). If a single bird was encountered multiple times, it was tallied only once.

The encounter rate is influenced by such factors as the size and conspicuousness of a species, density of human population, and whether the species is hunted, as well as by the geographic distribution of bird banders and the number of individuals of the species they handle. The encounter rate is also affected by the number of reports of birds encountered in the same 10′ block in which they were banded. Prior to 1958, encounters within 90 days at the site of banding were incorporated into the database (although the numbers are not large); in 1958, however, this practice was discontinued. Encounters at the site of banding more than 90 days after banding can still be submitted to the banding office; however, some banders do not submit such encounters, and not all of those sent in are actually entered into the database (L. Métras, pers. commun.).

Total no. encountered (1921-1995):

No. of encounters of birds banded in Canada (1921–1995) + no. of Canadian encounters of birds banded elsewhere (1921–1995)

All further calculations in this table are based on this set of encounters. Duplicate encounters of the same bird were excluded.

No. encountered from foreign bandings:

No. of the above encounters (1921-1995) that involved birds banded in another country but encountered in Canada

Maximum period from banding to encounter (mo.):

Maximum for any individual, rounded to the nearest month

This information is provided as an indicator of a bird's minimum age, so is not provided when date of encounter or actual date of death is highly uncertain. Note also that this figure does not represent longevity, except for birds banded as very young chicks, as no attempt was made to estimate the true age of the bird by guessing at its age when banded.

No. of Canadian-banded birds moving > 0 km:

This number gives the sample size for the calculation below.

Mean movement > 0 km of Canadian-banded birds:

(Sum of km moved for all encounters of Canadian-banded birds that moved > 0 km)
/ (No. of Canadian-banded birds moving > 0 km)

The distance between the banding and encounter locations of each record was computed using a great-circle distance — that is, the shortest distance that could be travelled between the two coordinates allowing for the curvature of the earth (Cowardin 1977; Additional details on data coding and analyses). Although the maps show straight lines connecting points of banding and encounter, no birds are likely to fly in an exact straight line, least of all seabirds, most of which will not overfly land and hence are constrained by the shape of coastlines. This is particularly important to bear in mind when considering birds banded in Hudson Bay or the Gulf of St. Lawrence and encountered on the U.S. east coast. These individuals must have travelled much farther than the straight-line distances suggest. Hence, mean movement should be treated as the absolute minimum distance that individuals had travelled between banding and encounter. Distance travelled is shown as approximate in records for which we assigned encounter coordinates (see explanation in section 4.2).

Maximum movement from all encounters (km):

Maximum calculated distance moved for any individual

Unlike the calculation for mean movement of Canadian-banded birds (above), the maximum distance is given for any encounter in the database, regardless of banding location.

% recovered (encountered dead):

((Total no. encountered dead) x 100) / (Total no. encountered)

Birds with "unknown" present condition codes were treated as dead for this calculation and the next one ("% direct recoveries"), as were birds banded in their Hatch Year and encountered in the same 10' block within three months of banding.

Birds encountered before 1965 and birds banded outside the North American banding scheme (mainly in Europe and Greenland) did not have true "present condition" codes to indicate whether the encountered bird was alive or dead. We assigned codes to these records based on available information to enable their inclusion in this calculation.

% direct recoveries:

((Total no. of direct recoveries) x 100) / (Total no. of encounters)

A direct recovery is an encounter with a bird "killed or found dead before, during, or immediately after the first period of migratory movement following banding and before return migration would be likely to have occurred" (Gustafson et al. 1997). Additional details on data coding and analyses shows how this designation was assigned; see also notes above on "% recovered."

The "% direct recoveries" is used chiefly as a measure of the hunting pressure on species in which most of the mortality is inflicted by hunters. In species that are not hunted, this figure is a rough guide to the magnitude of annual mortality. In the majority of species, this figure will be much higher for birds banded in their Hatch Year than for those banded in later years, reflecting the high mortality of juveniles typical of most birds.

% encountered during banding operations:

((Total no. encountered in banding operations) x 100) / (Total no. of encounters)

The number of birds encountered during banding operations was the sum of birds with "how obtained" codes of 89 or 99.

4.6 Banding effort map

The banding effort map shows the numbers of individuals for each species that were banded in Canada from 1955 to 1995 in each location (compiled by 10′ block, with blocks combined if too close to be shown separately on the map). This map helps the reader interpret the distribution of encounters, because it shows where banding effort has been concentrated. Under each map is a list of up to five of the master Canadian permit holders responsible for the most bandings of the species in Canada from 1955 to 1995 (listed in descending order). One to many individuals may band under a single master permit, so this listing does not necessarily identify the most prolific individual banders.

Date Modified: