A recent post on Tetrapod Zoology in which blogmaster Darren Naish rails against the well-meaning tradition of feeding bread to ducks got me thinking of another bird-feeding issue: chumming for pelagics.
My pelagic experience is limited, but on a couple of the trips I’ve been on the chum of choice was stale popcorn. This strikes me as insane. Gulls can probably digest almost anything, but the procellariiform birds that are the most sought-after prizes of pelagic excursions (shearwaters, petrels, albatrosses, etc.) have digestive systems adapted to digest protein. Why, other than economy, would we feed them almost pure carbs? The soft parts of popcorn probably disintegrate readily, but what do the hard bits do to the birds’ digestive systems? Given that these are pelagic birds, would we even know if they were dying like flies from popcorn impactions? Has anyone studied this? Talk me down, somebody…
Addendum: Procellariids do ingest some pretty formidable items. Bones, even fish otoliths, are rapidly dissolved by the birds’ digestive acids, but squid beaks (one of the hardest materials in nature) take weeks to break down. Gulls, terns, and many other seabirds can simply barf up indigestible materials, but procellariids have difficulty regurgitating solids (Furness et al. 1984). Combined with relatively small gizzard capacity, this makes them “especially susceptible” to deleterious effects from ingestion of indigestible materials (Azzarello & Van Vleet 1987).
More complex organic molecules require particular enzymes for processing. Just as many adult humans don’t produce the enzyme lactase and must avoid milk products, some birds such as thrushes (Witmer and Martínez del Rio 2001) don’t produce sucrase and must avoid sucrose-rich foods. Given their naturally low-carb diet, would we expect procellariids to produce starch-digesting amylase? If they don’t, does popcorn cause them intestinal distress similar to that suffered by lactose-intolerant humans and sucrose-intolerant thrushes?
But even if procellariids that eat the popcorn we chum with eventually end up barfing it up or breaking it down, is it their best interests or ours to trick them into wasting time and crop space on something that is at best of low nutritional value when more appropriate alternatives are available?