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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. . Wiley-Blackwell and Nordic Society Oikos are collaborating with JSTOR to digitize, preserve and extend access to Ornis Scandinavica. . 1992. Geometry of visual recruitment by seabirds to ephemeral foraging flocks. -Ornis Scand. 23: 49-62.Using geometric relationships, we calculate theoretical upper (20-30 km) and lower (0.7-6.2 km) limits to horizontal distances over which volant seabirds can be visually recruited to join Type I flocks in the open ocean. These are compared to empirical estimates for recruitment distances, obtained from chumming experiments conducted in the western Atlantic Ocean off the southeastern United States. The product of arrival times and flight speeds for individuals (n = 164) joining 10 flocks indicated that potential recruitment distances were closer to the lower theoretical limits, with a mean distance of 4.5 km when flight time and ground speed were adjusted for detection lags, wind speed, and zigzag flight. Distances and time spans for mutual attraction among seabirds have important consequences for evaluating both intraand inter-specific interactions at the community level, as well as direct implications for sampling independence during distributional surveys that employ consecutive line transects or other sequential counting methods.

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BackgroundWhile freshwater sustainability is generally defined as the provisioning of water for both people and the environment, in practice it is largely focused only on supplying water to furnish human population growth. Symptomatic of this is the state of Arizona, where rapid growth outside of the metropolitan Phoenix-Tucson corridor relies on the same groundwater that supplies year-round flow in rivers. Using Arizona as a case study, we present the first study in the southwestern United States that evaluates the potential impact of future population growth and water demand on streamflow depletion across multiple watersheds.Methodology/Principal FindingsWe modeled population growth and water demand through 2050 and used four scenarios to explore the potential effects of alternative growth and water management strategies on river flows. Under the base population projection, we found that rivers in seven of the 18 study watersheds could be dewatered due to municipal demand. Implementing alternative growth and water management strategies, however, could prevent four of these rivers from being dewatered.Conclusions/SignificanceThe window of opportunity to implement water management strategies is narrowing. Because impacts from groundwater extraction are cumulative and cannot be immediately reversed, proactive water management strategies should be implemented where groundwater will be used to support new municipal demand. Our approach provides a low-cost method to identify where alternative water and growth management strategies may have the most impact, and demonstrates that such strategies can maintain a continued water supply for both people and the environment.

A steep turbidity gradient across 3 shelf water masses and the Gulf Stream on the upper conhnental slope off the coast of the southeastern USA formed the basis for testing relationships between predator foragng tactics and relative detectability of prey. Censuses of seabirds were used to test a hypothesis originally proposed by Ainley (1977): plunge diving (plummeting from the air to subsequently capture prey underwater using the momentum of the fall) is more prevalent in clear as opposed to turbid surface waters. Twelve species of seabirds regularly used plunge bving to obtain prey in the study area: the tropicbirds Phaethon lepturus and P. aethereus, the boobies and gannet Sula dactylatra, S. leucogaster, and S. bassanus, respecbvely, and the terns Sterna maxima, S. sandvicensis, S. hirundo, S. paradisaea, S. forsteri, and S. antillarurn. Only P. lepturus was significantly more common in clear water. Five plunge-diving species were significantly more common in turbid waters. Neither the total number nor the proportion of plunge-diving bird species within the assemblage increased over more transparent waters. Significant decreases in the total number of plunge-diving individuals, and in the proportions of indviduals within the assemblage using plunge diving, occurred over waters with increasing transparency. Because the latter findings are directly counter to predictions arising from Ainley's hypothesis, we conclude that water clarity has yet to be clearly implicated as an influence on the allocation of foraging tactics in aerial seabirds.