Divorce in the long-lived and monogamous oystercatcher, <i>Haematopus ostralegus</i>:Incompatibility or choosing the better option?

Oystercatchers breeding on Schiermonnikoog divorced, because one of the mates deserted (leaving the partner as a victim of its choice), or because one or both mates were chased from the territory by usurpers. Though the majority of divorced birds were classified as victims, among birds that retained breeding status females more often chose to divorce than did males. Females changing mates were also more likely to move between territories than were males. A much larger database from Skokholm showed that the reproductive success of new pairs, which depended on the breeding history of the female only, was lower than that of old pairs. The suggestion that females benefited from divorce depended on the interpretation of the decrease in reproductive success with the new mate for widowed birds as an efficiency cost of mate change. However, the increase in reproductive success with duration of the pair bond for female first-time breeders and divorced females (but not for widowed females) may be linked to an increase in breeding age of the female, instead of a re-bound from initial inefficiency in reproduction with the new mate. Hence, competition for good mates and/or good territories appears the primary constraint on options for mate change for both males and females. The role of active choice and competition for good mates and/or good territories has been neglected in previous studies of divorce. The better option hypothesis takes account of both.<br/

Population consequences of winter habitat loss in a migratory shorebird: I. Estimating model parameters

1. In order to construct a model to predict the effect of winter habitat loss on the migratory population of the European subspecies of the oystercatcher, Haematopus ostralegus ostralegus, data on the reproductive and mortality rates collected throughout Europe over the last 60 years are reviewed. Within the Continental and Atlantic regions, inland-breeding and coastal-breeding subpopulations use the same coastal areas in winter. 2. Census and experimental data suggest pairs compete for territories and that an increasing proportion is excluded from breeding altogether, or nest in poor quality habitats, as the number of pairs attempting to breed increases. This provides a main source of density dependence in the basic model. 3. Mean clutch size, hatching success and fledging success were estimated for each subpopulation in each region. Data from one site suggested that the numbers fledged per breeding pair decreases as the total numbers of territories occupied increases, probably because of a reduction in chick survival. This additional source of density dependence was included in some versions of the model. 4. Most post-hedging mortality occurs in winter. Annual mortality was measured from the annual return rates of adults to the breeding areas and probably gives over-estimates. An additional 7-15% of adults die in severe winters once in 7 years in the Continental region but not in the milder Atlantic region. Oystercatchers in their first and second winter have a 20% higher winter mortality rate than adults. 5. The sometimes quite substantial annual fluctuations in the main production and mortality parameters were generally not correlated across sites within a subpopulation. This allowed the standard deviations of the annual variations in these parameters to be estimated for both subpopulations in each region so that realistic annual variations could also be included in the model

Peak morphological diversity in an ecotone unveiled in the chukar partridge by a novel Estimator in a Dependent Sample (EDS)

1. Areas of environmental transition (i.e. ecotones) have recently been shown to play an important role in the maintenance of genetic diversity, divergence and in speciation processes. We test the hypothesis that ecotone populations maintain high phenotypic diversity compared to other populations across the distribution range

The Messinian reef complex of the Salento Peninsula (Southern Italy): Stratigraphy, facies and paleoenvironmental interpretation

An integrated study of the early Messinian reef complex cropping out along the eastern coast of the Salento Peninsula (southern Italy), including stratigraphy, facies analysis and paleoecological aspects, is here presented. Fourteen facies types belonging to three main facies associations (back reef and shelf, shelf-edge, slope) have been recognized. They document a wide spectrum of depositional environments, reef building organisms and growth fabrics, in response to depth and other environmental factors in different parts of the reef complex. The biotic structure of the reef is also described and discussed in detail. It consists of different types of reef building organisms and of their bioconstructions (mainly Porites coral reefs, Halimeda bioherms and vermetidmicrobial trottoirs), that differ in composition and structure according to their position on the shelf edge-to-slope profile. Results indicate that the reef complex of the Salento Peninsula has strong similarities with the typical early Messinian reefs of the Mediterranean region. However, the recognition of some peculiar features, i.e. the remarkable occurrence of Halimeda bioherms and of vermetid-microbial trottoirs, gives new insights for better understanding reef patterns and development of the reef belt during the Late Miocene in the Mediterranean