Pepper, Palatability, and Pedagogy: Seed Choice and Competition in Campus Birds
Mark Stanback and Katie Lannon
Department of Biology, Davidson College
Abstract
We conducted an experiment to disentangle the roles
of palatability and interspecific competition on seed choice in Northern
Cardinals, House Finches, Tufted Titmice, and Carolina Chickadees. We hypothesized
that birds would prefer control sunflower seed over sunflower seed treated
with Squirrel-Away ®, a pepper-based additive. We further predicted
that consumption of "pepper seed" would reflect position in the
interspecific dominance hierarchy. Birds were presented with two identical
squirrel-proof feeders: one delivered control seed, the other delivered
pepper seed. Cardinals and House Finches exhibited significant preferences
for control seed while Titmice and Chickadees showed no significant preference.
However, when the effects of interspecific dominance were removed (i.e.
when analyses were restricted to visits made when the feeders were otherwise
empty or occupied by conspecifics or smaller species), Titmice also showed
a significant preference for control seed. Although competitively unhindered
Chickadees showed no significant preference for control seed, both Chickadees
and Titmice exhibited significant changes in seed choice during periods
of competitive release.
Introduction
Cayenne pepper-based seed additives have been marketed
in recent years as unpalatable to squirrels but of no consequence to birds.
If birds view pepper-treated seed as less palatable than untreated seed,
one might expect them to choose only untreated seed. However, the foraging
habits of birds are usually dictated by more than just food preferences.
The relative dominance of a given species in the local avifauna often influences
both its spatial and temporal foraging patterns. Although bird feeders offer
an excellent venue for observing interspecific dominance, interspecific
relationships are characterized by avoidance at least as much as they are
by agonistic interactions. To optimize their foraging, subordinate species
may voluntarily choose less preferred foods to avoid agonistic interactions
with more dominant species. To assess whether birds find pepper-based seed
additives unpalatable, my Vertebrate Field Zoology class examined seed choice
with respect to interspecific dominance in a campus population of birds.
Methods
Untreated sunflower seed and sunflower seed treated
with Squirrel-Away® were placed, respectively, in two identical, single-sided,
Absolute® squirrel-proof feeders.
The contents of the feeders were measured and the seed type was switched
three times during the four-week observation period (February 1997); data
collectors were unaware of the location of each seed type.
The feeder choices of the target species were recorded along with the location
and species identity of all other target species already present at either
feeder.
We initially analyzed for each species the number of visits made to each
feeder without regard to species already present at either feeder. To assess
the effects of interspecific competition, we limited our analyses to those
visits made in the absence of any larger species.
Conclusions
Cardinals and House Finches showed an overall preference for untreated seed.
Overall, Tufted Titmice and Carolina Chickadees showed no preference for
untreated seed.
When the effects of interspecific dominance were removed, Titmice were shown
to prefer untreated seed.
Competitively unhindered Chickadees showed no significant preference for
untreated seed, but both Titmice and Chickadees exhibited significant changes
in seed choice during periods of competitive release.
Visits to control and pepper feeders. All X2 tests performed with Yate's
correction.
Control |
Pepper |
X 2 |
P | |
| Seed Consumption | 10.5 liters |
5.52 liters |
||
| Feeding Visits | 2107 |
1264 |
105.16 |
< 0.001 |
| Carolina Chickadee: | ||||
| all visits | 312 |
334 |
0.34 |
ns |
| competition-free visits | 217 |
178 |
1.83 |
ns |
| Tufted Titmouse: | ||||
| all visits | 301 |
255 |
1.82 |
ns |
| competition-free visits | 222 |
130 |
11.76 |
<0.001 |
| House Finch: | ||||
| all visits | 661 |
291 |
71.51 |
<0.001 |
| competition-free visits | 400 |
164 |
48.96 |
<0.001 |
| Cardinal: | ||||
| all visits | 833 |
384 |
82.46 |
<0.001 |
| competition-free visits | 833 |
384 |
82.46 |
<0.001 |
This experiment was conducted by the Vertebrate Field Zoology class (Spring 1997).
