The food web pictured here (from a report by Gerry Sanger) illustrates the flow of mass and energy between invertebrates, fish and Procellariform seabirds in the Gulf of Alaska. Larger arrows indicate greater flow. Note how some species specialize on crustaceans such as copepods and euphausiids, while others eat larger forage species such as capelin or squid. The web gets more complicated as you add other members (not shown here) of the system such as seals, whales, other seabirds and predatory fish that consume the same kinds of prey. As top-level carnivores, seabirds may play an important role in structuring marine communities. Shearwaters are probably the most abundant seabird in Alaska during summer, and millions upon millions gather to feed in productive areas on our continental shelves. At times, their impact on local food webs and competing predators might be considerable. To understand how seabirds function in their environment and how they relate to other animals, we have to gather dietary data on a wide variety of species in many different areas.