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We compared the pronounced geographic pattern in the recolonization of Britain by the Eurasian Sparrowhawk (Accipiter nisus) from 1970 onward with the spatiotemporal pattern among House Sparrow (Passer domesticus) populations over the same period, using data on the occurrence of both species at garden feeding stations. Using a simulation of House Sparrow population trends based on a logistic model that incorporated a predation index derived from Eurasian Sparrowhawk incidence functions, we generated a close approximation to the unique trajectories among House Sparrow populations in rural and urban sites in different regions of Britain. We carried out further comparisons using two contrasting methods that focused solely on temporal patterns. We used estimates of the varying date of Eurasian Sparrowhawk recolonization at different sites to derive time variables in relation to recolonization date. One such relative time variable proved to be a better predictor of House Sparrow numbers than chronological time; ir indicated that House Sparrow numbers were generally stable or increasing prior to recolonization by Eurasian Sparrowhawks but declined continuously afterward. We also detected a significantly greater decrease in House Sparrow numbers when Eurasian Sparrowhawks were present using a method that compared annual changes in the abundance of prey species in the presence or absence of a predator. On the basis of these results, we argue that predation by Eurasian Sparrowhawks may be a sufficient explanation for the decline in House Sparrows in Britain. We also argue that urban House Sparrow populations' long-term release from predator pressure made them especially vulnerable when urban habitats were colonized by Eurasian Sparrowhawks. Received 3 April 2009, accepted 31 October 2009. Key words: Accipiter nisus, blitzkrieg hypothesis, Eurasian Sparrowhawk, House Sparrow, Passer domesticus, population limitation, predator--prey interaction, songbird declines, urban ecology. Nous avons compare le patron geographique de la recolonisation de la Grande-Bretagne par Accipiter nisus depuis 1970 et le patron spatiotemporel des populations de Passer domesticus au cours de la meme periode, a partir de donnees sur la presence des deux especes a des mangeoires. A l'aide d'une simulation des tendances des populations de P. domesticus basee sur un modele logistique incorporant un indice de predation derive de fonctions d'incidence de A. nisus, nous avons genere une bonne approximation des trajectoires uniques des populations de P. domesticus dans des sites ruraux et urbains de differentes regions de Grande-Bretagne. Nous avons effectue des comparaisons plus poussees a l'aide de deux methodes opposees qui portaient uniquement sur les patrons temporels. Nous avons utilise des estimations de la date de recolonisation d'A. nisus a differents sites pour deriver des variables temporelles. L'une de ces variables s'est averee etre un meilleur indice de l'abondance de P. domesticus que le temps chronologique; elle a indique que le nombre de P. domesticus etait generalement stable ou augmentait avant la recolonisation par A. nisus mais diminuait regulierement par la suite. Nous avons aussi detecte une baisse signincativement plus importante du nombre de P. domesticus lorsque A. nisus etait present, en utilisant une methode qui comparait les variations annuelles de l'abondance de l'espece-proie en presence ou en l'absence d'un predateur. Sur la base de ces resultats, nous croyons que la predation par A. nisus peut expliquer le declin de P. domesticus en Grande-Bretagne. Nous soutenons egalement que le relachement a long terme de la pression de predation sur les populations urbaines de P. domesticus les a rendues particulierement vulnerables lorsque les habitats urbains etaient colonises par A. nisus. DOI: 10.1525/auk.2009.09108

Because of their smaller size and isolation, island populations tend to be more divergent and less genetically variable than mainland populations. We collected DNA samples from nine Galapagos Hawk (Buteo galapagoensis) island populations, covering the species' entire range. Neutral minisatellite DNA markers were used to calculate within-island genetic diversity and between-island genetic differentiation ([F.sub.ST]). Typically, these markers mutate too quickly to be informative in such studies. However, in very small, isolated populations, concerns about high mutational rate are obviated by the relative force of genetic drift. Individuals within islands had the highest levels of reported genetic uniformity of any natural bird population, with mean within-population band-sharing similarity values ranging from 0.693 to 0.956, increasing with decreasing island size. Galapagos Hawks exhibit cooperative polyandry to varying degrees across islands; however, we did not find an association between degree of polyandry and genetic variability. Between-island [F.sub.ST] values ranged from 0.017 to 0.896, with an overall archipelago value of 0.538; thus, most populations were genetically distinct. Also, we documented higher levels of genetic similarity between nearby populations. Our results indicated negligible gene flow among most Galapagos Hawk populations, and genetic drift has played a strong role in determining structure at these minisatellite loci. Received 16 April 2004, accepted 5 April 2005. Key words: Buteo galapagoensis, cooperative polyandry, Galapagos Hawk, Galapagos Islands, genetic drift, minisatellites.

Previous interspecific studies have shown that migratory birds have a higher prevalence of blood parasites than nonmigratory birds. It is thought that birds that move greater distances are exposed to a larger parasite fauna, because of uneven distribution of vectors that carry such parasites. Current hypotheses also suggest that the stress of migration may allow parasites to persist, by weakening the immune system and allowing latent infections to recur. We captured migrating hatching-year Sharp-shinned Hawks (Accipiter striatus) in New Mexico and estimated natal latitudes of each individual by analyzing stable-hydrogen isotope ratios of feathers. That enabled us to estimate distances traveled up to point of capture. We also collected blood to quantify hematozoan infection prevalence and intensity. We related distance traveled to prevalence and intensity of hematozoan infections. Contrary to previous hypotheses, our results show no relationship between distance traveled by migrants and prevalence and intensity of hematozoan infections. Of 75 individuals examined, 24% were infected with Leucocytozoon toddi, 37% with Haemoproteus elani, and 5% with H. janovyi. To our knowledge, this is the first documented occurrence of H. janovyi in North America and in Sharp-shinned Hawks. Our stable-hydrogen isotope analyses indicated that H. janovyi was detected only in birds that originated in southwestern North America, which may be of significance in regard to biogeography of that parasite species.

Age-related trends in breeding performance of female Eurasian Sparrowhawks (Accipiter nisus) were examined in south Scotland. Over a 22 year period, most individuals were banded and of known age. Previous analyses had shown that average number of young raised per breeding attempt (or year) increased progressively in successive age-groups to midlife (around five years) and declined thereafter. Here we analyze different components of breeding performance (such as clutch-size, hatching and fledging success) to find which components contribute most importantly to the overall age-related trend in productivity. Most aspects of breeding showed a similar upward-downward trend through the life span, but the downward trend in productivity in later life could be attributed mainly to poorer nestling survival. In general, in each aspect of breeding, the mean trend of the population as a whole was followed by individuals studied at different ages. Such individual trends were sufficient to account for the overall mean trend, and there was no need to postulate that high-performance or low-performance birds entered and left the breeding population at different ages. Only one aspect of breeding showed no trend with age, namely proportion of birds that laid having built a nest, but that type of failure affected only a small proportion of individuals. Received 23 August 2001, accepted 10 April 2002.

Nonrandom pairings of Wisconsin Cooper's Hawks with respect to body mass have been observed. The behavior, which include findings of a disproportionate share in the subsequent breeding population from breeding adults of higher mass, indicate a direct correlation between nonrandom pairing and recruitment among falconiform species. The breeding behavior is explained through such factors as territory quality and the differential timing of migration patterns.

The offspring sex ratios for Cooper's Hawk were determined at 372 nests throughout Wisconsin from 1980 to 1995. The results revealed no significant differences in sex ratios at fertilization and at the nestling stage. However, the males were significantly more numerous at both stages, indicating that sex ratios at the fertilization and nestling stages were skewed toward males.