Summary 0[ Breeding sites of raptors were studied in relation to land!use and edge habitat using two di}erent scales in semi!arid Mediterranean landscapes in south!eastern Spain[ Habitat relationships were analysed using Generalized Linear Models[ 1[ The proportion of forest cover at a small scale was the best predictor for all species[ At a larger scale\ the proportion of forest cover was also a good predictor\ and the amount of edge habitat between forest and extensive agriculture was a very good predictor of booted and short!toed eagle densities[ 2[ Models for sedentary species of raptor were similar using both scales whereas trans!

Although metapopulation dynamics have become the focus of considerable theoretical research, little attention has been paid to its role when examining the coexistence of species. When two or more species live in the same patch network, interspecific interactions may affect their dispersal, colonization and extinction rates, and it may be possible to incorporate competition affecting these parameters in metapopulation models. Here, we extend the territorial occupancy model proposed by Lande to competing species. Our model estimates an equilibrium proportion of habitat occupancy as a function of life-history parameters, dispersal behavior, habitat suitability and interspecific interactions. Moreover, it could prove to be useful as a tool in the assessment of potential management decisions. We apply the model to the golden Aquila chrysaetos and the Bonelli's eagle Hieraaetus fasciatus, two territorial raptors that coexist in the Mediterranean region, sharing food and nesting habitats. Over the last twenty years, while the golden eagle has maintained and, in some cases, increased its breeding numbers, Bonelli's eagle has suffered a marked decline, with many territories abandoned by the latter now occupied by the former. This suggests that the dynamics of these species could be influenced by interspecific competition. The model identified the relative importance of competition (stable equilibrium that allows longterm coexistence) and predicted that, when habitat overlap is slight as in the study area, intraspecific dynamics are much more important for the persistence of each species than interspecific ones. Our results suggest that the improvement of territorial bird survival and productivity are the most urgently needed actions to be undertaken in the case of the golden eagle, while for Bonelli's eagle efforts should be focused on improving territorial and non-territorial bird survival. As habitat conservation measures, the proportion of suitable exclusive habitat should be increased for both species.

Fluid secretion by interlobular pancreatic ducts was determined by using video microscopy to measure the rate of swelling of isolated duct segments that had sealed following overnight culture. The aim was to compare the HCO 3 − requirement for secretin-evoked secretion in mouse, rat and guinea-pig pancreas. In mouse and rat ducts, fluid secretion could be evoked by 10 nM secretin and 5 µM forskolin in the absence of extracellular HCO 3 − . In guinea-pig ducts, however, fluid secretion was totally dependent on HCO 3 − . Forskolin-stimulated fluid secretion by mouse and rat ducts in the absence of HCO 3 − was dependent on extracellular Cl − and was completely inhibited by bumetanide (30 µM). It was therefore probably mediated by a basolateral Na + -K + -2Cl − cotransporter. In the presence of HCO 3 − , forskolin-stimulated fluid secretion was reduced ∼40% by bumetanide, ∼50% by inhibitors of basolateral HCO 3 − uptake (3 µM EIPA and 500 µM H 2 DIDS), and was totally abolished by simultaneous application of all three inhibitors. We conclude that the driving force for secretin-evoked fluid secretion by mouse and rat ducts is provided by parallel basolateral mechanisms: Na + -H + exchange and Na + -HCO 3 − cotransport mediating HCO 3 − uptake, and Na + -K + -2Cl − cotransport mediating Cl − uptake. The absence or inactivity of the Cl − uptake pathway in the guinea-pig pancreatic ducts may help to account for the much higher concentrations of HCO 3 − secreted in this species.

During a 7‐year research project in a forested area of southeastern Spain, we studied territorial occupancy and reproductive success in a Booted Eagle Hieraaetus pennatus population. We monitored 65 territories, gathering information on 406 occupancy events and 229 breeding attempts, including those of two potential competitors, the Northern Goshawk Accipiter gentilis and the Common Buzzard Buteo buteo. Generalized linear mixed models were used to explain occupancy and productivity, by evaluating the relative contribution of three different types of variables (habitat, competition and past events) and considering territory as a random effect. We examined a set of a priori hypothesized models, together with a number of additional models, and selected the best models following an information‐theoretic approach. Our best models related territorial occupancy and productivity to previous breeding success (the fledging of one or two young), which appeared to be the most important factor determining the probability of reoccupation and the reproductive output in the subsequent year. The best occupation model revealed that the probabilities of occupancy were also conditioned by a competition variable (intraspecific nearest‐neighbour distance) and two habitat variables (the location of the nest on the valley slope and the distance to the nearest forest track). Unlike the best occupation model, however, the selected model for reproductive output did not incorporate any competition variable besides previous breeding success, but included another two habitat variables (the effects of trunk height and NNE orientation).

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