Red-Shouldered Hawk Study
in Southern Ohio

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Genetics and Extra-pair Paternity Project

In 2018–2019, Ania Wrona, a graduate student at the University of North Texas, joined the research team to study the genetic structure and mating systems of suburban Red-shouldered Hawks. The team visited previously-known territories and determined whether nests were occupied. Nests were monitored from February – June (courtship through fledging). At selected nests, a researcher climbed to the nest during the nestling period; we banded the nestlings, and took a tiny blood sample before returning them to their nest. We also trapped parent hawks at most nest sites, banded them, took a small blood sample, and released them promptly. Trapping adult hawks was accomplished with one of two techniques. In some cases, we used a bal chatri trap covered with nooses and containing a mouse that served as bait (and was unharmed during the trapping). In other cases, a robotic fake owl surrounded by mist nets was used; the owl is a natural predator of Red-shouldered Hawks, which will dive at the owl and then become entangled in the nets. In all cases, we removed the birds from the trap immediately and released them unharmed after sampling and banding. The blood samples will be used for genetic testing and to determine parentage of the nestlings.

Until recently, birds that appeared to be monogamous (called “socially monogamous birds”) were assumed to also be sexually faithful pairs (“genetically monogamous”). However, advances in genetic techniques in the last 30 years have showed that fewer than 25% of all socially monogamous bird species practice true genetic monogamy. Among raptors, genetic monogamy seems to be the most common. However, few raptors species have been studied (<25), and even fewer of those occupy urban/suburban areas (<5). Among studies of extra-pair paternity (EPP) frequency in raptors, the highest rate of EPP was found in an urban population of Cooper’s Hawks in Milwaukee: 34% (15/44) of the broods analyzed in that population contained extra-pair young. It is not known how much the effects of their environment played a role in this breeding strategy, For her Master’s project, Ania will determine the EPP frequency in Red-shouldered Hawks through the use of molecular markers on blood samples acquired from adults and nestlings. Through this study, we will gain a better understanding of this species’ mating systems, and the factors that may influence it, such as breeding density, adult body size, and the number of young. Although the Cincinnati population of Red-shouldered Hawks appears to be stable at this time, urban and suburban landscapes are prone to rapid changes in amount of structures and available green spaces as the human population increases. Understanding how species are successfully reproducing under current conditions is vital to ensure the population’s ability to persist as humans continue to change the habitat around them.

Videos of Nesting Red-shouldered Hawks

YouTube channel
Cincinnati Red-shouldered Hawks

Video Monitoring Project - Sara Johnson Miller

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
 fledged young.
Of the 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 breeding pair.

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 State University.

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.  

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