Cornell University
In a new study that upends the way ornithologists think about a young
bird's diet -- but won't shock parents used to scanning the nutritional profile
of their children's food -- Cornell researchers have found that when it comes
to what chicks eat, quality trumps quantity.
In recent decades, many aerial insectivores, such as tree
swallows, have undergone steep population declines. Cornell researchers have
demonstrated for the first time that the fatty acid composition in the tree
swallow diet plays a key role in chick health and survival rates, potentially
pointing to new ways to protect fragile bird species.
"This study really reforms the way ecologists see the food of wild animals," said senior author David Winkler, professor of ecology and evolutionary biology in the College of Agriculture and Life Sciences. "From a preoccupation with how much food is available, we need to turn our eyes to what kind of food is available."
For the study, researchers manipulated the ratio of long-chain
omega-3 fatty acids [the good fat present in fish oil] to short-chain omega-3
fatty acids [the good fat in flax seeds] as well as the amount of food.
Chicks
given diets rich in long-chain omega-3 polyunsaturated fatty acids (LCPUFA)
grew faster, were in better condition, had more efficient metabolisms and had a
stronger immune response compared with chicks on a low LCPUFA diet.
The researchers found that chicks had higher growth rates and
better body condition when they were fed a small amount of high-quality food
than if they were fed a large amount of low-quality food.
In addition, chicks fed a small amount of high-quality food had
similar immune responses and metabolic rates as those fed a large amount of
low-quality food.
In the wild, tree swallows and other aerial insectivores
typically forage on a mixture of aquatic and terrestrial insects. Aquatic
insects are much richer in LCPUFA than insects that live on land.
"We found that aquatic insects are likely a far more
important food source than previously thought due to their high-quality
fats," said lead author Lily Twining, a doctoral student in the field of
ecology and evolutionary biology. "The destruction and degradation of
aquatic habitats that produce insects with long-chain omega-3 fatty acids may
be having important negative impacts on tree swallows and other declining
aerial insectivores.
"This study provides new clues into how nutrition and food
webs impact the decline of prominent species, and provides further incentive to
protect freshwater habitats not only for aquatic animals like fish, but also
for terrestrial animals like the songbirds in our study," she added.
Tree swallow populations have declined 36 percent in the past
three decades, a circumstance explained at times by reduced insect populations,
ecological fragmentation and the effects of climate change. Other North American
aerial insectivores -- like nighthawks and chimney swifts -- have also
undergone similar major disruptions in populations.
This study suggests that the mismatch between the fatty acid
composition of insects and the nutritional needs of aerial insectivores could
be a crucial driver of fitness and reproductive potential for these birds.
Furthermore, the researchers said tree swallows may be timing
breeding to coincide with the peak abundance of high-LCPUFA aquatic insects.
