Year Eight of the Los Angeles Raptor Study once again produced a remarkable pool of data on hawk, owl and falcon nesting activity over the same geographic areas as the last few years. For the 2024 nesting season, numbers were up from the previous two years for our four major species: Cooper’s Hawk, Red-tailed Hawk, Red-shouldered Hawk and Great Horned Owl. This notable increase includes the number of active territories, active nests and the total number of fledged birds.

More important than breaking records, we had the opportunity to analyze data on a species-by-species basis to shed light on territory re-use, non-breeding pairs, nest takeovers, nest switches (takeovers by other species), and more. The goal of the study is to understand the year-to-year trends and to discover the forces at work involving our local raptors in the Los Angeles area. Apex predators play an important role in the ecosystem, especially in our complex urban setting where human influences can alter balances. What better place than Los Angeles to study urban raptors?

In late September, the LA Raptor Study 2024 Final Report was presented to a well-attended audience via Zoom. The Study represents the only comprehensive dataset of an entire breeding raptor community within the urban core of Los Angeles, per Dr. Dan Cooper (Cooper Ecological Monitoring, Inc.), who directed the launch of the Study in 2017.

Nurit Katz, the Study’s Outreach Coordinator, has elevated communication and education capabilities with our volunteers and the public since 2022. Nurit was a raptor study volunteer, monitoring nests prior to her taking on her current role, and she is also employed as UCLA’s Chief Sustainability Officer.

The study has become a recognized model for “community science” within Los Angeles, with clear scientific goals and plethora of data being collected by community scientist volunteers who undergo training on scientific methods.

Apply to Volunteer in 2025

Details for participating in the study are discussed on FoGP’s “Raptor Study & Resources” webpage where you can also find a link to a Volunteer Application. In January, registered volunteers are invited to a virtual training session and a field training workshop held in early February. Nest assignments are then made. Dan, Nurit, and myself also help orient new volunteers at their assigned nest sites.

Since Cooper’s Hawks are late-nesters and present special challenges in tracking, a second virtual session and field training are offered specifically for this species in April. Cooper’s Hawk nest assignments are made for ambitious, willing volunteers, and nearly all volunteers want one!

Study Result Highlights in 2024

650 raptor territories were rechecked or discovered across the study area, representing 239 Cooper’s territories (vs. 222 in 2023), 215 Red-tailed Hawk territories (vs. 184 in 2023), 57 Red-shouldered Hawk territories (vs. 55 in 2023), 105 Great Horned Owl territories (vs. 84 in 2023), as well as a handful of territories of American Kestrel, Peregrine Falcon, Barn Owl and Western Screech-owl.

While not all of these territories were found to be active in 2024, the numbers continue to closely reflect the maximum number of territories in the study area, thanks to increased effort and our growing knowledge of local species ecology. The study puts focus on the territories of breeding pairs which, for the most part, mate for life, but don’t necessarily use the same nests from year to year.

Fledge Rates

We define Fledge Rate results as fledged nests for territories tracked; the fledge rate of active nests, on the other hand, is extremely high, with few failures once birds start incubating. Convergence of the Fledge Rate this year for the three focal hawk species is interesting and unexpected, considering they were quite different in the previous few years:

• Red-tailed Hawk: 127 nests fledged from 169 active territories (75%). This fledging rate saw a return to average after the higher rates of 2020 and 2021 and lower rates in 2022 and 2023.

• Cooper’s Hawk: 88 nests fledged from 113 active territories (78%). This rate of success was slightly below the average across the past five years, up from the last two years.

• Red-shouldered Hawk: 27 nests fledged from 36 active territories (75%). This proportion is higher than the prior two years and the 5-year average, but lower than in 2020.

• Great Horned Owl: The analysis for this species changed this year, because we added new territories based upon more than only active nests found, ­such as pairs that duet. We found that 40 nests fledged from 58 territories, but any comparison to previous years would be invalid.

Territory Re-occupancy

Red-tailed Hawks kept their amazing and steady territory re-occupancy rate of 80%. The other two hawk species’ re-occupancy rates have been more variable over the years of study. Red-shouldered Hawks were around 75% in 2024. The lowest rates were for Cooper’s Hawks at roughly 65%, which is well above the previous two-year 50% average territory re-occupancy rate. Only these hawk species were included in this analysis. There are plans to dig deeper into the data to explore nest structure re-use, in addition to focusing on territory re-use.

Nest Productivity

While there was a significant increase across all four major species in the total number of fledged young, nest productivity rate is measured as the mean number of chicks hatched from successful active nests (with failed/abandoned nests excluded). Interestingly, this metric peaked in 2019 across our four species. There is no explanation. It is possible that two very wet winters was not enough to overcome the previous drought trend in place, and we continue to explore possible correlations with seasonal weather.

Over the study period (2017-2024), mean nest productivity number (chicks per nest) varied in a fairly tight range of 1.8 for Red-shouldered Hawks to a high of 2.5 for Cooper’s Hawks.

Our Special Species

There is limited data from the study on the rarer local raptor species, including American Kestrel, Peregrine Falcon and Western Screech-owl.

The study closely tracks one peregrine pair in Griffith Park. Two other peregrine nest locations were confirmed on top of high buildings this year where juvenile rescues took place. Several other tall structures are also suspected host sites for nesting, but collecting data is difficult due to building management challenges. We plan to put more effort to following these peregrines in coming years.

Cavity-nesting American Kestrels also prove challenging, but one residential-area nest in Boyle Heights was monitored and another territory in Sepulveda Basin was confirmed with four post-fledged juveniles observed.

Work done by students under the UCLA Institute of Environment and Sustainability Senior Practicum, with FoGP as their client, addressed breeding owl species including Barn Owls and Western Screech-owls. Students successfully contributed with nocturnal field surveys and predictive distribution modeling. More detail is available on FoGP’s raptor webpage.

Nest Disturbance and Tree Trimming

A new focus of the study involves documenting nest disturbances such as nests lost to wind, tree-trimming or trees being chopped down. It is illegal to trim out nests even when it is done between nesting seasons. It is also illegal to disturb active nests in any manner which may adversely affect reproductive success. We have observed that the destruction of nests is often unintentional on the part of residents.

In 2024, to address the significant trimming issues observed, we created signs to place on accessible nest trees. The signs include information about applicable laws protecting nests. Template letters were also created to inform homeowners and area residents of nests on their properties. These measures represent a proactive educational approach to prevent loss of nests.

Another disturbance involves loss of raptors through secondary poisoning by rodenticides. We hope that the California bans on two classes of anticoagulants will alleviate the senseless death of raptors that ironically serve a vital role in rodent control. FoGP and many other organizations have fought hard for these legislative actions; we’re finally nearing the goal line.

The Raptor Study family of participants celebrated a fantastic year of accomplishments at the Volunteer Appreciation Dinner held in Griffith Park this fall. FoGP thanks our volunteers, our talented science team, and the public agencies that provided access and services, along with L.A. residents who provided so many great tips! Let’s keep up the momentum!

~ Gerry Hans
photo: Gerry Hans