The entire population of the California Condor ( Gymnogyps californianus) probably contains fewer than 50 individuals (Wilbur 1976(Wilbur , 1978. Within its recorded history the species has shown a continual decline in numbers. During the past decade there has been an especially alarming decrease in condor recruitment. Between 1968 and 1975 the entire population averaged only 1.5 young fledged per year with a maximum of two produced any single year (Wilbur 1978).Mortality factors which historically have reduccd the condor population (Koford 1953) cannot account for the observed recent decrease in productivity. Lowered reproductive success in numerous other bird species in recent years has been associated with eggshell thinning caused almost exclusively by p,p' DDE, the principal metabolite of DDT (Cooke 1973, Stickel1975, Peakall 1975). In this paper we document thinning and other structural changes in California Condor eggshells, verify the presence of DDE in the thin eggs, and suggest that the "DDT syndrome" has contributed to lowered nesting success. Comparisons are made to the changes induced by the experimental feeding of DDE to the structure of eggshells of another falconiform species, the American Kestrel (F&o sparverius) . MATERIALS AND METHODSDuring the late 1960' s, a former U.S. Fish and Wildlife Service biologist, Fred C. Sibley, regularly visited all condor nests thought to have been used recently in order to monitor reproductive activity. During his visit to each nest, Sibley strained the loose substrate from the floor of the cavity through a fine-meshed screen. Sharp rocks, bone fragments and other debris which might pose a danger to an egg were removed, and all eggshell fragments he found were collected. Between 1966 and 1969, he obtained at least eight samples of eggshell fragments of known year of origin from six different condor nest sites, and he made them available to us for study. In addition, Eben McMillan provided 11s with shell fragments of a broken condor egg that he found in a nest in 1964. Wilbur and John Borneman collected fragments from another nest in 1976, and a party directed by Wilbur secured four more samples in November 1977. In order to detect changes in shell thickness, these fragments and intact California Condor eggshells in the Western Foundation of Vertebrate Zoology collection were measured with a model 35 PS Federal bench comparator thickness gauge, or with a modified Starrett Model 1010 M micrometer. We attempted to measure only specimens that had intact shell membranes tightly affixed to the true shell. However, some samples of fragments totally lacked shell membranes. To the measured thickness of these we added 0.10 mm, the mean thickness of normal California Condor eggshell membranes, as compensation. Whole eggs were measured on the egg equator through the blow-hole near the middle of one side, whereas we couldn' t tell what part of the eggshell the fragments came from. Condor eggshell fragments taken in 1896. 1922. -1964, 1966, 1967 and i969, and those of control...

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Scoping reviews, in which the literature on a given topic is systematically collated and summarized, aid literature searches and highlight knowledge gaps on a given topic, thus hastening scientific progress and informing conservation efforts. Because much research and conservation is targeted at the species level, ornithology and bird conservation would benefit from scoping reviews of individual species. We present and apply a framework for scoping reviews for three disparate raptor species: California Condor Gymnogyps californianus, Harpy Eagle Harpia harpyja and Gyrfalcon Falco rusticolus. We consulted expert panels to develop appropriate search strings and lists of essential literature, i.e. ‘benchmark articles’. We searched Web of Science, Scopus and Google Scholar. Searches for California Condor, Harpy Eagle and Gyrfalcon returned 268, 138 and 343 articles, respectively, that discuss, review or collect empirical data for the focal species. Our searches returned all benchmark articles identified by species experts, indicating that the searches captured the most important work on each species. We coded each study according to the topic addressed, country and month in which data were collected. We also coded threats, stresses and conservation actions addressed by studies, following definitions used by the International Union for the Conservation of Nature (IUCN) during Red List assessments. Literature summaries for each species include the number of studies addressing certain topics, monthly timing of research and global maps of research focus. Our coding scheme revealed important knowledge gaps for each species. Effects of conservation actions on wild individuals were less studied for California Condors. Harpy Eagles were less studied outside of Brazil and Panama, and Gyrfalcons were less studied outside of their breeding season. Scoping reviews of the world's bird species would help to identify critical knowledge gaps, thereby aiding the global effort to assuage the sixth mass extinction.