PRBO Conservation Science
Quarterly Journal of PRBO Conservation Science, Number 160, Spring 2010: PRBO's Graduate Students




  

A Birder's Feast—Dense Gatherings, Possible Surprises

Feeding Frenzies

Rich Stallcup


 
PRBO's Graduate Students
Stewart Udall and the Future of Conservation
Grad Student Profiles
A Past Grad Student Reflects
PRBO Highlights
Investing in Nature's Future
Focus on Feeding Frenzies
Letter to the Editor
 


Brown Pelicans. Photos on this page by Rich Stallcup/PRBO.
Feeding frenzies happen when there is a hungry population of animals and a sudden infusion of food. There are many examples of such events in birds, but frenzies are not limited to Aves. Ants and flies swarm on a dead grouse. Wolves and bears quarrel violently over a downed caribou calf. Orcas go crazy in a pod of sea lions, and sea lions lose any composure they may have had when gobbling at a salmon run.

Among land-based creatures, birds are second only to insects in the frequency and variety of their frenzies. Depending on the kind of event, different species are attracted, and the diversity can be of great interest to birders.

Ciconiformes (herons and egrets) gather as if by magic at drying wetlands, where stranded amphibians and fish become easy pickins'. In California, the occasional Little Blue or Tricolored Heron shows up among the Great Blue Herons and white egrets.
A concentration of scaup and other waterbirds on Tomales Bay.

Herring runs at central California estuaries are frenzied by cormorants, loons, grebes, gulls, and huge numbers of mixed species of diving ducks, sometimes including a Tufted, an Oldsquaw, or even an eider.

Magpies, ravens, and Turkey Vultures often chase each other and snatch bits of flesh from a recently deceased tule elk in the southern San Joaquin Valley. At such feasts Golden Eagles will soon appear (and, up until 30 years ago, California Condors).

A school of young anchovies in a tidal slough may be savaged by egrets running on the shore, Red-breasted Mergansers below the water, and terns plunge-diving from the air. There is nowhere for the fish to shelter, and the whole forage may begin and end in a few minutes.

When larger anchovies (or sardines) school in quiet waters of bays, bigger fish, porpoises, or pinnipeds may variously press them towards the surface. That attracts cormorants, gulls, and Brown Pelicans, which use their different strategies to decimate the prey from above.

For people who seek the rare, feeding frenzies on the open ocean (sometimes seeable from shore with a good scope) are most exciting. Causes vary, from the sudden appearance of drifting pelagic red crabs, to upwellings of euphausid shrimp and dead rockfish, squid outbursts, fish parts discarded from boats (unrefined shark liver oil is most attractive) or, best of all, the broken-up remains of a dead whale or seal.
A gathering of fulmars near a sea-birding boat.

When this type of event happens near shore, a good birder may be able to pick out fulmars, shearwaters, and the occasional Parasitic Jaeger or albatross from the more usual suspects. When it happens well offshore, especially near the continental shelf break (where seabirds from all compass directions tend to concentrate), the unexpected is practically routine. Large numbers of Black-footed Albatrosses (and occasional individuals of four or five other albatross species) are often first on the scene. If stinky organic oil is present, so may be storm-petrels. In season, curious Sabine's Gulls and Arctic Terns will arrive and, consequently, the pirates—Pomarine and Long-tailed Jaegers and skuas! There is always the remote chance of some far-flung Pterodroma like a Cooks, Murphy's or Scaled Petrel, or the holy grail for California sea birders, a Procellaria—a White-chinned, Parkinson's or (maybe soon) a Westland Petrel.
Among the regular ducks at a feeding event, an Oldsquaw (Long-tailed Duck), center-left.

Feeding frenzies are life-and-death, survival-of-the-strongest events. For the participants, there are winners and losers. For field ornithologists, they can be wildly exciting and intellectually challenging.

"Did you see what I think I just saw?!?"

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