DORCHESTER — The trade is in.

The Pittsburgh Zoo & Aquarium and Boston's Franklin Park Zoo have agreed to a straight-up swap of gorillas, Pittsburgh announced Thursday. Dorchester is sending out a 33-year-old silverback. Pittsburgh is sending back a 7-year-old male bachelor.

The deal, per both clubs: Franklin Park Zoo's veteran silverback Little Joe (33) heads west to anchor Pittsburgh's family group. In return, the Pittsburgh-born Frankie (7) heads east to join Dorchester's newly assembled bachelor crew.

The deal

OUT — to Pittsburgh

LITTLE JOE

Species: Western lowland gorilla (Gorilla gorilla gorilla)
Age: 33
Sex: Male — full silverback
Boston tenure: more than two decades at Franklin Park
Profile (per Pittsburgh's release): "curious, intelligent and gentle"; strong with unrelated juveniles; plus-grade puzzle-feeder solver
Career notable: the September 2003 enclosure escape that injured a 2-year-old girl and triggered a Franklin Park containment overhaul (per CBS Boston)
New role: silverback over a four-gorilla family — 29-year-old female Moka, 35-year-old female Ibo, and youngsters Charlotte (3) and Bo (2)
Intro window: four to seven weeks of trust-building before he's physically in with the troop, per Pittsburgh assistant mammal curator Karen Vacco

What Pittsburgh fans can expect. Wild lifespan for the species runs roughly 30 to 40; in zoo care, gorillas regularly reach 50 and have been documented past 60. Joe at 33 is in the senior end of his prime but still well inside the leadership window for a captive silverback. A typical adult male weighs roughly 300 to 400 pounds — north of 6 feet upright with the chest, shoulders and saddle that give silverbacks their name. Pittsburgh fans should expect classic silverback behaviors once introductions clear: chest-beating displays, peacekeeping among the troop, paternal supervision of the youngsters Charlotte and Bo. He is being brought in to lead a family. That is the job description.

IN — to Dorchester

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FRANKIE

Species: Western lowland gorilla (Gorilla gorilla gorilla)
Age: 7
Sex: Male — late juvenile, on the cusp of "blackback"
Birthplace: Pittsburgh Zoo, 2018
Dam: Moka — the same Moka who is now Joe's new troop matriarch
Profile (per his Pittsburgh keepers): "good vibes — playful and chill"
New role: joins Franklin Park's new bachelor group with 5-year-old Pablo and 8-year-old Moke (acquired earlier this spring from the Smithsonian's National Zoo, per CBS Boston). An anchor silverback for the bachelors is expected later in the year.

What Boston fans can expect. Male gorillas hit physical adulthood around age 8 and enter the "blackback" stage between 8 and 12, with the silver saddle starting to come in around 10. By 12 to 14 they are full silverbacks. Frankie is 7 — meaning Dorchester is acquiring a gorilla on the very edge of that transition. Expect him to put on substantial mass over the next five to eight years, broaden through the chest and shoulders, and develop the gray-saddle markings that define adult males. In the wild, young males his age leave their natal group; in accredited zoos, bachelor troops mimic that natural dispersal and give late-juvenile males a place to practice social bonds before they ever lead a family. Boston is getting him at the developmental sweet spot.

The trade clears under the American Association of Zoos & Aquariums' Gorilla Species Survival Plan — the coordinated breeding-and-placement program AZA-accredited zoos use to keep critically endangered western lowland gorillas genetically diverse in human care. In plain English: Joe gets the chance to be a father. Frankie gets a fresh start with bachelors his own age. The species gets a healthier gene pool.

What it means

For Dorchester: this is a rebuild. The Franklin Park gorilla room is going younger and going single — three bachelors, eventually four with an inbound silverback. The veteran face of the franchise is leaving, but the timeline is moving forward.

For Pittsburgh: this is a win-now move. Joe is a seasoned silverback walking into a ready-made family. If the four-to-seven-week intro goes to plan, that troop is operational this summer.

For more than two decades, Little Joe has been the headline act at the Franklin Park gorilla yard — the silverback guests came to see, the one keepers leaned on to anchor the troop and to draw the crowd. Generations of Dorchester schoolkids grew up on field trips that ended at his glass.

He is also the same silverback who, in September 2003, made the most famous gorilla escape in Boston history — slipping his enclosure, getting loose on zoo grounds, and injuring a 2-year-old girl before he was tranquilized and recaptured. The zoo overhauled its containment after the incident. Two decades later he remained the star of the building.

Zoo New England president Stephanie Brinley framed the call in the original April 21 announcement:

"This news is bittersweet to share as we will all miss Little Joe, but we are also excited for this opportunity for him to lead his own troop and start a family."

Franklin Park assistant curator Erica Farrell told CBS Boston the new Dorchester group is being built with growth in mind.

"We hope that Pablo will bond with his new bachelor troop members while they are still young and develop relationships that will help them grow together," Farrell said.

Joe is expected to move to Pittsburgh in the coming months. Frankie's arrival in Dorchester is on the same window.

A bachelor group going up. A silverback going down to start his family. The trade is final.

Done deal: Boston ships veteran silverback Little Joe to Pittsburgh, picks up 7-year-old prospect Frankie

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