16 



Birds — Our Liviiii^ Rtwoiirctw 



Hestbeck's "Canada Geese," Hupp et al., all this 

 section) have shown some impressive gains 

 over the past decades, but most gains have been 

 registered by large-bodied geese, with several 

 smaller species and smaller subspecies of the 

 highly variable Canada goose {Branta caiuulcii- 

 sis) having depressed populations. 



Censusing and determining the status of nat- 

 ural Canada goose populations are made more 

 difficult by the widespread introduction and 

 establishment of resident goose populations, 

 which breed outside the traditional Arctic nest- 

 ing areas and mix with migratory populations 

 on the wintering grounds. 



Duck surveys address more than 30 species 

 that might be legally hunted. Even though some 

 species are stable or even increasing, many 

 duck populations have declined in the past 

 decade (Caithamer and Smith, this section). 

 Biologists attribute these declines to losses of 

 breeding and wintering habitats and a long peri- 

 od of drought in breeding areas. Among species 

 receiving special emphasis, canvasbacks 

 (,4\t/Mfl valisineria: Hohman et al., this section) 

 showed a complex pattern with regional 

 changes in distribution and abundance, and pin- 

 tails [Anns acuta: Hestbeck"s "Decline of 

 Northern Pintails," this section) showed a wide- 

 spread and nearly consistent pattern of decline. 



Results are preliminary, but two new census 

 programs, the MAPS and BBIRD programs 

 (Martin et al., this section), promise to provide 

 much higher quality information on status and 

 trends by measuring not only the presence of 

 bird populations in breeding areas, but also their 

 success. When fully operational, this approach 

 may offer important clues regarding the causes 

 of observed population changes. 



Shorebirds are highly migratory, and status 

 and trends of their populations are largely deter- 

 mined from observations made during periods 

 in their life cycles in which birds congregate in 

 limited breeding, staging, or migratory stopover 

 areas. Populations of eastern (Harrington, this 

 section) and western (Gill et al., this section) 

 species show general patterns of decline, 

 although soine species, including those using 

 inland areas, are too poorly studied to detect 

 trends. Apparent dependence on critical breed- 

 ing and staging areas suggests that populations 

 of many species are vulnerable to habitat loss 

 and disturbance, 



Seabirds in the Pacific region (Carter et al.. 

 Hatch and Piatt, both this section) include many 

 diverse species that respond differently to fac- 

 tors such as human proximity to nesting areas, 

 oil spills, introduction of predators, depletion of 

 fishery stocks, and availability of human refuse 

 as food. Some species, including certain gulls, 

 brown pelicans {Pelecanus occidciiuilis), and 

 double-crested cormorants {Phalacrocurax 



aiiritus), have responded positively to recent 

 changes in some areas, whereas others, includ- 

 ing munelets and munes (Family Alcidae) and 

 kittiwakes (Genus Ri.ssa). have shown declining 

 trends. Populations of other species appear to 

 fluctuate widely, and information for many 

 species is insufficient to determine long-term 

 trends. 



Colonial waterbirds of the continental and 

 east coast regions of the United States (Erwin, 

 this section) show trends related to many of the 

 same factors operating in the Pacific region, 

 with some species recovering from past losses 

 from pesticides while some other species that 

 exploit human refuse are increasing dramatical- 

 ly. Populations of other species, especially cer- 

 tain terns, are declining, probably as a result of 

 habitat loss and degradation or other kinds of 

 human disturbance. Special efforts have been 

 made to determine status and trends of the pip- 

 ing plover (Chanuhius inclodiis: Haig and 

 Plissner. this section), a species listed as endan- 

 gered in certain parts of its range and as threat- 

 ened in others. 



Populations of raptors (Fuller et al., this sec- 

 tion) are difficult to census, but ospreys 

 (Puiuliou haliaeliis). bald eagles {Haliaeetiis 

 leucocephalits). and peregrine falcons (Falco 

 pcregrimis) have increased in numbers as they 

 recover from past effects of pesticides. 

 Populations of most vultures, hawks, and owls 

 are either poorly known or believed to be stable. 

 Notable exceptions are California condors 

 (Gymnogyps califaniiamis: Pattee and Mesta, 

 this section), the crested caracara {Caracara 

 plancus: Layne. this section), and spotted owls 

 (Stri.x occidentalis), all of which enjoy or have 

 been considered for additional protection. 

 Mortality factors of eagles (Franson et al., this 

 section) have been monitored and, although 

 these data do not directly measure population 

 status, they do indicate trends in the kinds of 

 factors that tend to depress population growth. 



The wild turkey (Meleagris gallopavo; 

 Dickson, this section) has shown dramatic 

 increases in distribution and abundance in 

 recent decades because of translocations, habi- 

 tat restoration, and harvest control. Mourning 

 doves {Zenaida macroiira: Dolton. this section) 

 have shown generally stable populations, 

 although recent population declines in the west- 

 em states are disturbing. Regional increases of 

 ravens (Corviis corax) in the southwest 

 (Boarman and Berry, this section) are primarily 

 of concern because of their potential effects as 

 predators on eggs and young of the desert tor- 

 toise (Gophenis agassizu)- 



Populations of severely endangered species, 

 like the California condor (Pattee and Mesta, 

 this section), the Mississippi sandhill crane 

 (Gnis canadensis piilla: Gee and Hereford, this 



