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TURQUOISE TANAGER

Why were the songbird chicks dying?

About 10 years ago, Watts and Tim Snyder, curator of Birds not eat the new, improved pellets. “I can make the perfect
at Brookfield Zoo, began a series of studies to understand why diet with the nutrients an animal needs,” said Watts,
many of the zoo’s songbird chicks—across various species— “but if the animal doesn’t eat it, it’s worthless.”
were not surviving. After ruling out environmental issues, The problem, thought Watts and Snyder, was the birds
they zeroed in on the birds’ diets. weren’t identifying the pellets as food. “In the wild they’d
The birds’ diets were formulated based on what is known be going for food with a high-sugar content,” said Snyder,
about poultry and parrots, which have been well studied. “and foods have to be a certain color to be ripe.” They did
“What we’re finding out is that may be a good starting point, a series of studies changing one variable at a time—pellet
but all birds are not the same,” said Snyder. size, sugar content, and color. On testing pellets with various
Among other things, the birds were fed a nutritionally levels of sugar, they found one the birds seemed to favor.
complete, low-iron commercial diet for birds because they, One Variable at a Time
like other fruit-eating birds, are susceptible to iron-overload
disease. This deadly disease is caused by the build-up of iron Next, they experimented with the color of the pellet. The birds
in the birds’ major organs. The low-iron diet helped the preferred red pellets over the original yellowish shade. “They
birds live longer, but they weren’t successfully reproducing. all went for a medium-red color, except for the troupials and
orioles, which in the wild go for dark berries like cherries
A Hunch and mulberries,” said Snyder.
Watts had a hunch that the baby birds were anemic. “We had It’s a very protracted study, said Watts. “We change a
lowered the iron so much for the parents that there wasn’t variable, wait for the next breeding season, assess egg produc-
enough iron in the yolk. So contrary to what everybody else tion and chick production to see if it improved. If not, we
was doing, we put them on a normal iron diet.” At breeding make another change and wait for the next breeding season,
time the following year, the survivability of the chicks and so on.” This ongoing study is an example of how complex
improved, but not enough. nutrition research can often be.
On further study, Watts discovered another variable at work: “We’re seeing incremental improvements so hopefully we’re
The birds were deficient in vitamin D. She worked with Mazuri, on the right track,” said Watts. For example, certain songbird
the manufacturer of the commercial diet, to develop a custom species have fledged at the zoo for the first time, including
pellet that delivered more vitamin D. However, the birds did the curl-crested aracari and the Andean cock-of-the-rock.

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