Heat capacities of aqueous solutions of Na 2 SO 4 and Na 2 CO 3 up to near saturation (1.9 and 2.5 mol‚kg -1 , respectively) and of NaOH (to 7 mol‚kg -1 ) have been measured at 25 °C with a Picker flow calorimeter. The calorimeter performance was checked using concentrated NaCl(aq) solutions. On the basis of these measurements, an experimental protocol suitable for the reliable determination of the heat capacities of concentrated electrolyte solutions by Picker calorimetry was established. The heat capacities for Na 2 -SO 4 (aq), Na 2 CO 3 (aq), and NaOH(aq) and literature data for the apparent molar volumes of NaOH(aq) at 25 °C were correlated using the Pitzer formalism. A number of inadequacies in previous models at high concentrations and for extrapolation to infinite dilution are discussed. In particular, it has been confirmed that the heat capacity data for Na 2 CO 3 (aq) at low concentrations must be corrected for the hydrolysis of the carbonate ion. Standard partial molar heat capacities for the three salts and the standard partial molar volume of NaOH(aq) have been derived at 25 °C.

Summary 1.Movement patterns of predators should allow them to detect and respond to prey patches at different spatial scales, particularly through the adoption of area-restricted search (ARS) behaviour. Here we use fine-scale movement and activity data combined with first-passage time (FPT) analysis to examine the foraging strategy of northern gannets Morus bassanus in the western North Sea, and to test the following hypotheses: (i) birds adopt a hierarchical foraging strategy characterized by nested ARS behaviour; (ii) the locations and characteristics of ARS zones are strongly influenced by physical oceanography; (iii) the initiation of ARS behaviour is triggered by the detection and pursuit of prey; (iv) ARS behaviour is strongly linked to increased foraging effort, particularly within nested ARS areas. 2. Birds on 13 of 15 foraging trips adopted ARS behaviour at a scale of 9·1 ± 1·9 km, and birds on 10 of these 13 trips adopted a second, nested ARS scale of 1·5 ± 0·8 km, supporting hypothesis 1 above. ARS zones were located 117 ± 55 km from the colony and over half were within 5 km of a tidal mixing front ~50 km offshore, supporting hypothesis 2 above. 3. The initiation of ARS behaviour was usually followed after only a short time interval (typicallỹ 5 min) by the commencement of diving. Gannets do not dive until after they have located prey, and so this pattern strongly suggests that ARS behaviour was triggered by prey detection, supporting hypothesis 3 above. However, ~33% of dives in mixed coastal water and 16% of dives in stratified water were not associated with any detectable ARS behaviour. Hence, while ARS behaviour resulted from the detection and pursuit of prey, encounters with prey species did not inevitably induce ARS behaviour. 4. Following the initiation of ARS behaviour, dive rates were almost four times higher within ARS zones than elsewhere and almost three times higher in zones with nested ARS behaviour than in those without, supporting hypothesis 4 above and suggesting that the foraging success of birds was linked to their ability to match the hierarchical distribution of prey.

Many procellariiform (tube-nosed) seabirds employ a dual-foraging strategy involving repeated alternation of short and long foraging trips. For species breeding at sites around the Southern Ocean, long trips typically extend to areas of enhanced productivity at great distance from the nest. Evidence concerning the use of such areas during dual-foraging in other oceanographic regions is, however, limited. The present study examines the foraging strategy, locations and behaviour at sea of Cory's shearwaters in the Azores, a chain of 9 islands and associated islets in 3 groups straddling the mid-Atlantic ridge (MAR) in the North Atlantic Ocean. Adults used a dual-foraging strategy with an average of 3 short (1 to 4 d) trips followed by a long trip of up to 20 d (average 9 d). Short trips were evenly distributed around breeding sites within an average range of 75 km, whereas long trips without exception headed north of the Azores and extended up to 1800 km from the nest. Core foraging areas for long trips were within apparent regions of enhanced productivity resulting from cold water upwelling along the MAR north of the colony (for birds from the central Azores) or over the western flank of the MAR northwest of the colony (for birds from the western Azores). On long trips from all 3 island groups birds also visited an additional area of enhanced productivity in the region of Flemish Cap, close to the North American continental shelf edge. Birds commuted to and from distant foraging sites relatively quickly (25 km h -1 on average), but individual parents did not co-ordinate their foraging activity to reduce the frequency of nights when chicks were unfed. As a result, chicks experienced much longer intervals between feeds (up to 9 nights) than conspecifics at other North Atlantic islands in the absence of dual-foraging (maximum 4 nights). However, chicks in the Azores received much larger meals when they were fed, and so the overall food provisioning rate (g d

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