Saddleback Journal of Biology - Saddleback College

Spring 2010 Biology 3B Paper
pattern, as no mentions are made pertaining to the
spatial distribution of resources. In an effort to
differentiate those feeding area distributions from the
arrangement which existed in this study, researchers
have termed areas with mixed source, widely-spaced
feeding areas “natural/artificial decentralized feeding
areas,” or NADFA, and areas with a centrally located
and artificial source as “artificial concentrated feeding
areas”, or ACFA. In this study, researchers are
interested in studying whether the frequency of highcost
territorial displays and resource availability so
often studied in NADFA also exists in ACFA with a
dense population of feeding hummingbirds. Though
the density of hummingbirds and space limitations
differ from previous studies, the type of behaviors
displayed by individuals can only exist as far as their
energy budget. It is therefore hypothesized that when
resources are depressed, a lower frequency of highintensity
behaviors will be exhibited.
Method and Materials
This study was conducted at a residential
three-and-a-half acre avocado grove located in
Bonsall, CA, for a duration of four days during mid-
March 2010. The daytime temperatures averaged
between 22.8-23.9 o C and wind speeds averaged
3.5mph. The hummingbird feeders were located on the
residences’ back porch, facing the lower half of the
avocado grove. Based on years of observations and
the abundance of occupied and abandoned nests
discovered on the premises by grove owners, the home
range (Brown and Orians, 1970) of the population of
Anna’s hummingbirds studied remains within the
grove’s perimeter and possibly within adjacent lots.
These “resident” hummingbirds have been provided
with nine large commercial feeders containing a
consistent supply of an approximately 1.16M sucrose
solution for the past six years. Each feeder has seven
feeding stations resembling a red and yellow flower
and has the capacity to hold 0.960L of solution. While
these resident hummingbirds are not tagged and no
official counts have been made, it is estimated by
grove owners that the Anna’s population numbers
between 100-200 individuals, depending on the
season. Other species of hummingbirds, such as
Rufous, Black-Chinned, and Calliope, have
additionally been observed residing on the grove but
only in seasonal durations. Researchers of this study
took great care in assuring that videotaping was
completed prior to the migrational introduction of non-
Anna’s species.
The residence’s partially enclosed back porch
uses five large evenly spaced pillars for support; two
outside pillars and three middle pillars. Attached to the
trim between each middle pillar are three hooks for the
suspension hummingbird feeders. Nine total feeders
are supported by this arrangement. As the resident
hummingbirds are accustomed to nine feeders (or 63
feeding stations) at any given time, researchers
considered this arrangement “high-resource”
availability. When only three feeders were provided, a
66% depression in resources, it was considered “lowresource”
availability.
Maintaining a consistent sucrose content for each day
of the study, the researchers designated the first and
third days of the study as high-resource and the second
and fourth days as low-resource. The spaces
immediately between the three middle pillars were
successively videotaped for 40 minutes each day
resulting in a total of eight hours of footage: four
hours of high-resource footage and four hours of lowresource
footage. Afterwards the footage was
analyzed and each incident of territoriality exhibited
next to a feeder quantified and categorized as either a
high-intensity or low-intensity display based on the
behavioral descriptions of previous studies (Ewald and
Orians, 1982; Ewald and Carpenter, 1978; Brown,
1969). According to Brown and Orians 1970’s study, a
territory is defined as “…a fixed area, which may
change slightly over a period of time, [where] acts of
territorial defense by the possessors evoke escape and
avoidance in rivals so that…the area becomes an
exclusive area with respect to rivals.” The intent of
this study was to focus on the territorial displays
exhibited strictly at the ACFA, therefore researchers
did not examine the territorial spatial distributions of
areas outside the ACFA’s perimeter. Researchers
defined the area between two pillars as a territory,
which is approximately 340 cubic feet.
For purposes of quantifying low-and-highintensity
chase occurrences, researchers designed the
following: (1) low-intensity chases were those which
remained within the scope of the camera lens, since a
defending hummingbird need only chase an intruding
hummingbird a relatively short distance in order to
ensure the invader leaves the territory; and (2) highintensity
chases were considered those which
continued beyond the scope of the camera lens, as
more energy was needed by defenders to chase
intruders the longer distance. Gorget displays,
typically the first territorial behavior exhibited by
hummingbirds before increasing the severity of their
warnings (Sibley, 2001), and consequently the
associated energy allocation, are distinctive enough
low-cost behaviors that researchers needed only to
use conventional descriptions in order to recognize
and quantify occurrences. According to Ewald and
Orians’ 1982 study, gorget displays are “an
energetically inexpensive method of defense in which
the owner moves its head from side to side while
facing the intruder.” Males additionally flash the
fuchsia colored iridescent feathers on their crowns to
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Saddleback Journal of Biology
Spring 2010