The National Audubon Society Christmas Bird Count (CBC) is an early-winter survey of birds. Although counts occur in Central and South America, most CBCs occur in North America. The sample area for a count is a circle that is 15 miles in diameter, and varying numbers of volunteers count all birds they see in the circle during a single day, which is within 2 weeks of 25 December. (Butcher 1990)
Although this analysis only considers the interval 1959 - 1988, the CBC was begun in 1900. The number of circles and participants has changed dramatically since the early years. Butcher (1990) notes that 1,508 circles were surveyed in 1986-1987. Unfortunately, the number of birds counted is a function of effort, and analysis of change over time must incorporate some effort adjustment (Butcher and McCulloch 1990). In this analysis, we standardized the counts to birds/100 party hours, but we acknowledge that more research is needed into methods of adjusting counts.
Each year, American Birds publishes a summary of the previous years count (e.g., American Birds 47(4):1-1026) that notes interesting features of the counts and summarizes birds, effort, and volunteers for each circle. Also, numerous articles have appeared in American Birds that summarize data for individual species and groups of species. Root (1988) has summarized patterns of regional relative abundance for wintering North American birds.
Taxonomic problems with the database
Several species are grouped in the database, and several transcription errors have occurred in collating the data. In Table 1, we note species that are incorrectly grouped in the database. Also, many categories exist for rare or unidentified birds. In Table 2, we list the taxa that we have eliminated because of possible taxonomic problems.
Species with small sample sizes
Because the CBC is an early winter survey, many migrant species appear in the database. Because species seen on few circles could provide misleading views of population trends, we have eliminated species with small sample sizes (fewer than 40) from display.
These species are listed in Table 3.
Literature Cited Butcher, G. S. 1990. Audubon Christmas Bird Counts. Pp. 5-13 in J. R. Sauer and S. Droege, eds. Survey designs and statistical methods for the estimation of avian population trends. U.S. Fish Wildl. Serv. Biol. Rep. 90(1). Butcher, G. S., and C. E. McCulloch 1990. The influence of observer effort on the number of individual birds recorded on Christmas Bird Counts. Pp. 120-129 in J. R. Sauer and S. Droege, eds. Survey designs and statistical methods for the estimation of avian population trends. U.S. Fish Wildl. Serv. Biol. Rep. 90(1). Root, T. 1988. Atlas of wintering North American birds. University of Chicago Press, Chicago, Il.
Table 1. Species that are incorrectly grouped in the database. A '*' indicates that the combined data appears under that name.
Grouped Species 1. Western grebe, Clark's grebe. 2. Red-breasted sapsucker, Yellow-bell. sapsucker, Red-naped sapsucker. 3. Gilded flicker, Yellow-shafted flicker, Red-shafted flicker, Northern Flicker*. 4. Tufted titmouse*, Black-crested titmouse. 5. Canyon towhee, Brown towhee. 6. Great-tailed grackle, Boat-tailed grackle. 7. Myrtle warbler, Audubon's warbler, Yellow-rumped warbler.
Table 2. Taxonomic groups that are found in the CBC database, but are of questionably validity for trend analysis. These groups include birds not identified to species, some species not commonly found in North America during the breeding season, and species with taxonomic changes that have not been consistently identified in the database.
"AOU" Taxon identifier Number of Circles 3333 unidentified_accipiter_ unac 853 12 aechmophorus_spp_______ **** 27 5769 aimophila_spp__________ **** 6 345 alcidae_spp____________ **** 68 5509 ammodramus_spp_________ **** 4 4289 archilochus_spp________ **** 26 3669 asio_spp_______________ **** 23 51830 nanday_(black-hooded)_p **** 22 930 black-vented_shearwater bvsh 15 4989 emberizidae/blackbird_s bkbd 487 5971 blue_bunting___________ blbu 4 7669 sialia/bluebird_spp____ **** 14 4832 brown_jay______________ brja 4 3822 budgerigar_____________ budg 26 3451 unidentified_buteo_spp_ bute 687 1326 anus/black_x_mallard_sp **** 134 5911 california_towhee______ calt 111 2211 caribbean_coot_________ cact 16 5169 carpodacus_spp_________ **** 66 7559 catharus_spp___________ **** 15 64239 chaetura_spp___________ **** 6 7351 chickadee_species______ chic 94 7621 clay-colored_robin_____ ccro 3 3095 common_peafowl_________ cope 4 1207 phalacrocorax/cormor_sp corm 139 4879 corvus_spp_____________ **** 6 5219 loxia/crossbill_spp____ **** 33 4889 corvus/crow_spp________ **** 116 4689 empidonaz/d_or_h_flycat **** 15 1339 anatidae/dabbling_duck_ **** 3 909 procellariidae/d-backed **** 29 1639 melanitta/d-winged_scot **** 4 6509 dendroica_spp__________ **** 21 1499 anatidae/diving_duck_sp **** 6 2327 limnodromus/dowitcher_s dowi 191 1327 unidentified_duck______ duck 581 3499 accipitridae/eagle_spp_ **** 121 1579 anatidae/eider_spp_____ **** 18 4679 empidonax_spp__________ empi 131 3154 european_collared_dove_ **** 8 5099 euphagus_spp___________ **** 8 3559 falco/falcon_spp_______ **** 302 5189 emberizidae/finch_spp__ **** 64 5742 five-striped_sparrow___ fssp 2 4449 tyrannidae/flycatcher_s **** 12 7519 polioptila/gnat-catch_s **** 23 4169 caprimulgidae/goatsucke **** 12 1519 bucephala/goldeneye_spp **** 52 5299 carduelis/goldfinch_spp **** 26 1697 unidentified_goose_____ goos 69 37 podicipedidae/grebe_spp greb 74 11230 green_parakeet_________ **** 8 2979 phasianidae/grouse_spp_ **** 16 534 larus/gull_spp_________ gull 578 3333 accipitridae/hawk_spp__ hawk 853 6224 hawaii_oo______________ haoo 33 17520 hill_mynah_____________ himy 6 3271 hook-billed_kite_______ hbki 3 4401 unidentified_hummingbir humm 114 4123 hybrid_flicker_________ **** 8 1326 hybrid_mallard_________ hybm 134 1861 threskiornithidae_spp__ **** 25 387 stercorarius/jaeger_spp jaeg 65 4779 corvidae/jay_SPP_______ **** 9 5677 junco/junco_spp________ junc 97 7489 regulus/kinglet_spp____ **** 25 3333 accipiter/large_spp____ **** 853 349 alcidae/large_spp______ **** 11 3559 falco/large_spp________ **** 302 534 larus/large_spp________ **** 578 3669 strigiformes/large_spp_ **** 23 2089 rallus/large_spp_______ **** 28 909 procellariidae/l-backed **** 29 5387 calcarius/longspur_spp_ long 74 77 gavia/loon_spp_________ loon 128 5012 unident._meadowlark____ unme 326 1299 anatidae/merganser_spp_ **** 168 4891 mexican_crow___________ tacr 6 3824 monk_parakeet__________ mopa 72 309 uria/murre_spp_________ **** 23 219 alcidae/murrelet_spp___ **** 20 10210 muscovy_duck___________ mudu 3 4529 myiarchus_spp__________ **** 15 2029 nycticorax/night_heron_ **** 12 4207 chordeiles/nighthawk_sp nigh 14 7279 sitta/nuthatch_spp_____ **** 16 6799 oporornis_spp__________ **** 21 11290 orange-fronted_parakeet ofpa 6 5039 emberizidae/oriole_spp_ **** 9 3687 strigiformes/owl_spp___ owl. 308 3829 psittacideae/parakeet_s **** 17 3829 psittacidaee/parrot_spp **** 17 2477 scolopacidae/peep_spp__ peep 216 2247 phalaropus_spp_________ phal 22 5959 pheucticus_spp_________ **** 12 1861 plegadis_spp___________ **** 25 2709 charadriidae/plover_spp **** 13 2929 phasianidae/quail_spp__ **** 15 2089 rallus/rail_spp________ **** 28 2089 rallus_spp_____________ **** 28 4869 corvus/raven_spp_______ **** 33 5279 carduelis/redpole_spp__ **** 37 11580 red-lored_parrot_______ **** 4 3823 rose-ringed_parakeet___ rrpa 17 7622 rufous-backed_robin____ rbro 11 4123 redxyellow_shafted_flic **** 8 2567 scolopacidae/sandpiper_ spip 166 4022 sphyrapicus/sapsucker_s **** 27 1489 aythya/scaup_spp_______ scau 472 1657 melanitta/scoter_spp___ scot 189 3737 otus/screech-owl_spp___ sowl 981 4329 selasphorus_spp________ **** 61 909 charadriiformes/shorebi **** 29 6227 lanius/shrike_spp______ shri 92 3333 accipiter/small________ **** 853 3559 falco/small____________ **** 302 3669 strigidae/small________ **** 23 634 sterna/small___________ **** 85 5409 sparrow_spp____________ **** 400 5599 spizella_spp___________ **** 9 634 sterna_spp_____________ ster 85 6101 stripe-headed_tanager__ shta 3 6149 hirundinidae/swallow_sp **** 83 1799 cygnus/swan_spp________ **** 35 4229 apodidae/swift_________ **** 6 6099 emberizidae/tanager_spp **** 4 1389 anas/teal_spp__________ **** 60 634 sterna/tern_spp________ tern 85 431 thayer's_gull__________ thgu 195 7029 mimidae/thrasher_spp___ **** 13 7599 muscicapidae/thrush____ **** 65 7319 parus/titmouse_spp_____ **** 6 7029 toxostoma_spp__________ **** 13 1491 tufted_duck____________ tudu 22 4459 tyrannus_spp___________ **** 3 6409 vermivora_spp__________ **** 5 6249 vireo_spp______________ **** 9 3269 cathartidae_spp________ **** 6 6399 emberizidae/warbler_spp **** 105 6199 bombycilla/waxwing_spp_ **** 30 4642 w._flycatcher_complex__ wefl 48 0011 clarks_grebe___________ clgr -- 12 western_grebe__________ **** 27 4401 unident._hummingbird___ unhu 114 534 larus/white-winged_gull **** 578 4660 traill's_flycatcher____ trfl 4 4089 woodpecker_spp_________ **** 83 7139 troglodytidae/wren_spp_ **** 66 11600 yellow-headed_parrot___ **** 9 2549 yellow_leg_spp_________ **** 87 2549 tringa/yellowlegs_spp__ **** 87 3131 rock_dove______________ rodo 1709
Table 3. Species seen on fewer than 40 CBC circles.
"AOU" Species name Number of Circles 5920 abert's_towhee_________ abto 35 4650 acadian_flycatcher_____ acfl 2 4340 allen's_hummingbird____ alhu 24 5031 altamira_oriole________ alor 7 1820 greater_flamingo_______ gflm 10 3980 strickland's_woodpecker stwo 12 1080 ashy_storm-petrel______ aspe 5 1080 ashy_storm-petrel______ aspe 5 130 atlantic_puffin________ atpu 19 5030 audubon's_oriole_______ auor 7 920 audubon's_shearwater___ aush 3 2410 baird's_sandpiper______ basa 26 5450 baird's_sparrow________ brds 34 6160 bank_swallow___________ bnks 24 1770 black-bell._whist._duck bbwd 37 1770 black-bell._whist._duck bbwd 37 4720 n._beardless-tyrannulet nbty 9 6330 bell's_vireo___________ bevi 26 7080 bendire's_thrasher_____ beth 33 1140 masked_booby___________ mabo 5 3880 black-billed_cuckoo____ bbcu 4 6620 blackburnian_warbler___ blbw 18 810 black-foot._albatross__ bfal 5 5030 audubon's_oriole_______ auor 7 6610 blackpoll_warbler______ bplw 10 1070 black_storm-petrel_____ bspe 5 3450 common_black-hawk______ cbha 9 770 black_tern_____________ blte 23 4530 brown-crest._flycatcher bcfl 15 4940 bobolink_______________ bobo 16 3710 boreal_owl_____________ boow 18 5760 botteri's_sparrow______ bosp 3 4410 broad-bill._hummingbird brbh 16 7340 bridled_titmouse_______ brti 26 1150 brown_booby____________ brbo 9 4320 broad-tail._hummingbird btlh 13 4390 buff-bel._hummingbird__ bubh 22 4270 blue-thr._hummingbird__ bthh 4 6410 blue-winged_warbler____ bwwa 8 3240 california_condor______ caco 2 6860 canada_warbler_________ cawa 11 6121 cave_swallow___________ casw 5 3825 canary-winged_parakeet_ cwpa 14 3110 plain_chachalaca_______ plch 10 4230 chimney_swift__________ chsw 4 6590 chestnut-sided_warbler_ cswa 24 6120 cliff_swallow__________ clsw 15 3450 common_black-hawk______ cbha 9 4200 common_nighthawk_______ coni 32 4190 common_pauraque________ copa 21 130 atlantic_puffin________ atpu 19 6780 connecticut_warbler____ conw 8 4600 greater_pewee__________ grpe 15 4461 couch's_kingbird_______ coki 25 4931 crested_mynah__________ crmy 7 4550 dusky-capped_flycatcher dcfl 8 4690 dusky_flycatcher_______ dufl 17 4610 eastern_wood-pewee_____ ewpe 33 660 elegant_tern___________ elte 10 3890 elegant_trogon_________ eltr 4 3810 elf_owl________________ elow 2 1760 emperor_goose__________ emgo 13 5261 european_goldfinch_____ eugo 6 4730 eurasian_skylark_______ eusk 6 6883 eurasian_tree_sparrow__ etsp 26 3300 snail_kite_____________ snki 10 3800 ferruginous_pygmy-owl__ fpow 5 3800 ferruginous_pygmy-owl__ fpow 5 951 flesh-footed_shearwater flfs 6 1050 fork-tail._storm-petrel ftsp 3 1050 fork-tail._storm-petrel ftsp 3 4110 gila_woodpecker________ giwo 37 1820 greater_flamingo_______ gflm 10 4490 great_kiskadee_________ gkis 20 4600 greater_pewee__________ grpe 15 890 greater_shearwater_____ grsh 6 4830 green_jay______________ grnj 14 3910 green_kingfisher_______ gkgf 27 3092 green_pheasant_________ **** 2 3460 gray_hawk______________ grha 8 4450 gray_kingbird__________ gknb 8 6340 gray_vireo_____________ grvi 8 4820 gray-breasted_jay______ gbja 22 4680 hammond's_flycatcher___ hafl 17 6090 hepatic_tanager________ heta 13 6840 hooded_warbler_________ howa 15 390 ivory_gull_____________ ivgu 12 2880 northern_jacana________ noja 4 6770 kentucky_warbler_______ kewa 13 4490 great_kiskadee_________ gkis 20 5990 lazuli_bunting_________ lazb 19 4670 least_flycatcher_______ lefl 30 50 least_grebe____________ legr 34 740 least_tern_____________ lete 29 7110 le_conte's_thrasher____ lcth 18 3070 lesser_prairie_chicken_ lpch 6 4210 lesser_nighthawk_______ leni 22 5031 altamira_oriole________ alor 7 7060 long-billed_thrasher___ lbth 27 6760 louisiana_waterthrush__ lowa 26 6430 lucy's_warbler_________ luwa 8 6800 macgillivray's_warbler_ macw 31 4260 magnificent_hummingbird mahu 7 3860 mangrove_cuckoo________ macu 7 900 manx_shearwater________ mash 22 1140 masked_booby___________ mabo 5 1680 masked_duck____________ madu 9 4820 gray-breasted_jay______ gbja 22 5700 yellow-eyed_junco______ yeju 13 3290 mississippi_kite_______ miki 4 2960 montezuma_quail________ mtzq 20 2810 mountain_plover________ moup 38 6790 mourning_warbler_______ mowa 3 4720 n._beardless-tyrannulet nbty 9 2880 northern_jacana________ noja 4 2230 red-necked_phalarope___ rpha 37 6490 tropical_parula________ trpa 5 5860 olive_sparrow__________ olsp 20 6510 olive_warbler__________ olwa 11 4590 olive-sided_flycatcher_ osfl 10 5060 orchard_oriole_________ oror 35 951 flesh-footed_shearwater flfs 6 6880 painted_redstart_______ pare 15 4190 common_pauraque________ copa 21 6260 philadelphia_vireo_____ phvi 15 910 pink-footed_shearwater_ pkfs 15 3110 plain_chachalaca_______ plch 10 6370 prothonotary_warbler___ prow 30 6110 purple_martin__________ puma 26 3130 red-billed_pigeon______ rbpi 3 3826 red-crowned_parrot_____ rcpa 16 6240 red-eyed_vireo_________ revi 22 2230 red-necked_phalarope___ rpha 37 3901 ringed_kingfisher______ riki 17 4260 magnificent_hummingbird mahu 7 2356 rock_sandpiper_________ rosa 34 720 roseate_tern___________ rost 6 4411 rose-throated_becard___ rtbe 4 2600 ruff___________________ ruff 15 5790 rufous-winged_sparrow__ rwsp 24 3090 sage_grouse____________ sagr 39 1850 scarlet_ibis___________ scib 4 6080 scarlet_tanager________ scta 10 5040 scott's_oriole_________ scor 36 3440 short-tailed_hawk______ stha 19 960 short-tailed_shearwater stsh 27 4730 eurasian_skylark_______ eusk 6 960 short-tailed_shearwater sbsh 27 3830 smooth-billed_ani______ sban 27 5370 smith's_longspur_______ smlo 37 3300 snail_kite_____________ snki 10 950 sooty_shearwater_______ sosh 34 5032 spot-breasted_oriole___ sbor 5 3151 spotted_dove___________ spdo 32 3980 strickland's_woodpecker stwo 12 4451 thick-billed_kingbird__ tbki 7 4460 tropical_kingbird______ trki 26 6490 tropical_parula________ trpa 5 120 tufted_puffin__________ tupu 12 6000 varied_bunting_________ vabu 2 4240 vaux's_swift___________ vasw 17 7560 veery__________________ veer 28 6440 virginia's_warbler_____ viwa 9 2590 wandering_tattler______ wata 39 6270 warbling_vireo_________ wavi 17 4620 western_wood-pewee_____ wwpe 12 3140 white-crowned_pigeon___ wcpi 7 6020 white-collar._seedeater wcse 4 3180 white-tipped_dove______ wtdo 10 3731 whiskered_screech-owl__ whso 6 2040 whooping_crane_________ whcr 5 2400 white-rumped_sandpiper_ wrsa 25 3731 whiskered_screech-owl__ whso 6 3180 white-tipped_dove______ wtdo 10 3410 white-tailed_hawk______ wtha 31 3040 white-tailed_ptarmigan_ wtpt 7 4530 brown-crest._flycatcher bcfl 15 3010 willow_ptarmigan_______ wipt 12 6390 worm-eating_warbler____ wewa 24 250 xantus'_murrelet_______ xamu 9 4630 yellow-bell._flycatcher ybfl 4 80 yellow-billed_loon_____ yblo 38 5700 yellow-eyed_junco______ yeju 13 491 yellow-footed_gull_____ yfgu 2 2150 yellow_rail____________ yera 24 3400 zone-tailed_hawk_______ ztha 8