In 2011 and 2012, Sara Johnson Miller, then a
graduate student at Arkansas State University, joined the research team
and used video time-lapse cameras
to study nesting behavior in Cincinnati.
The team visited previously-known territories and determined whether
they were occupied (e.g., hawk present, nests with fresh sticks or green
vegetation lining) – over 250 territories were visited. Nests were
monitored from February - June (pre-laying until
fledging). At selected nests, 24 h/day digital infra-red
video cameras were installed. Cheryl & Jeff did the climbing, while Sara and Melinda
provided ground support & processed chicks. Video was recorded with
micro-DVRs and the system was powered by a deep-cycle marine battery,
and Sara replaced memory cards and batteries on a 3-day cycle.
At 15 nests, cameras were installed at occupied nests prior to
egg-laying. At 10 nests, cameras went up after eggs hatched, when
the nestlings were estimated to be 3-12 days old. The cameras remained
in place until the nest failed or fledged young. Within the first week
of hatching, nestlings were marked on their heads and backs with Sprayolo non-toxic liquid livestock dye to facilitate differentiation of
nestlings in the video. Researchers also climbed again to band (USGS & colored
number-letter bands) the nestlings and to re-paint their heads after
initial paint began to fade.
Sara extracted data from the
14,800+ hours of video that were recorded. Data extracted during video
review included adult behavior during clutch initiation, causes of nest failure, nestling behavior and
aggression rates, prey delivery rates and prey types. In addition to the
25 camera nests, the team also monitored the territories that became
occupied until nests failed or
15 nests that received a camera prior to egg-laying, all pairs
laid eggs, and most of these pairs fledged young, while the remaining
nests failed due to predation or nest disturbance. These results show
that mounting the cameras during the courtship phase, after the adults
occupied the nest, did not seem to disturb the birds. This method also
provided more accurate and complete data for an entire nesting period
than mounting cameras post-hatching.
Of the 10 nests that received and retained a camera post-hatch, mostl
fledged young. However, after installing one camera post-hatch, Jeff
discovered that the female parent was avoiding the nest, although the
male had no qualms about delivering abundant prey. Fortunately, this
unusual case was caught within 24-hours of camera installation, and
allowed the team to act quickly to remove the disturbing camera and
allow behaviors to return to normal. The team is happy to report that
this nest successfully fledged all three of its nestlings. This incident
illustrated individual birds’ different tolerance levels for
nest disturbance. It also furthers the argument for installing cameras
prior to egg-laying, because it minimizes consequences of disturbing the
There is good evidence to support the idea that RSHAs
have partial incubation, and Sara found start of incubation varied among individuals but many birds
began full incubation with the laying of
the penultimate egg. The video data showed that more sibling
aggression occurred during week 2 than during week 3. These data suggest that the
dominance hierarchy is established early and may influence
the probability of success of each nestling through the remainder of the
nestling period, and perhaps even after fledging.
Prey types delivered to nests was similar to that described previously
by the team (from conducting direct observation of nests) and included
small mammals, frogs and other amphibians, snakes, and invertebrates.
This indicates that this population of suburban RSHAs are indeed
generalist predators, similar to populations nesting in more typical,
remote forested habitats.
Causes of nest failure or chick mortality were depredation by
Great-horned Owls and a raccoon, and a three-week battle
between a pair of nesting RSHAs and an Eastern gray squirrel, which the
squirrel ultimately won. The team is happy to report that the
pair re-nested in a new location and successfully fledged two chicks,
albeit also in the company of several squirrels!
Our video monitoring
of nests provided new insights into incubation behavior and sibling
relationships and yielded valuable information on predation and other
causes of nest failure.
Sara has finished her Master's thesis and it is available from Arkansas
The video monitoring project would not be possible without the support
of the RSHA Team, RAPTOR Inc., Hawk Mountain Sanctuary,
The Audubon Society of Ohio, Arkansas Audubon Society Trust, Arkansas
State University, and all of the, cooperative landowners in Cincinnati.