A prestigious US wildlife conservation group is facing new pressure to distance itself from its namesake’s racist past after two Audubon Society chapters and its employees’ union announced they were dropping his name from their titles.

The society at a national level has been mulling for more than two years how to handle its association with John James Audubon, a prominent 19th-century artist, naturalist and slave owner whose detailed, colourful paintings in the book The Birds of America set the gold standard for generations of ornithologists.

Now, amid a wider racial justice reckoning following the 2020 murder of George Floyd, chapters in Portland and Chicago, and the staff union formerly known as Audubon for All, are acting unilaterally to sever the name of the white supremacist with a shameful record of buying and selling slaves.

“Starting today we disavow the name. We will not elevate and celebrate a person who would reject and oppress our union members today,” the newly named Bird Union, representing dozens of Audubon employees, said in a statement.

“John James Audubon [was] a racist white man who enslaved at least nine Black people and contributed to Samuel George Morton’s ‘race science’, which claimed white superiority over other races, ideas criticised at the time and now discredited.

“Changing our name is a small step to demonstrate our commitment to anti-racism.”

Announcing its decision to rename itself on Tuesday, the Portland Audubon Society said it “cannot continue to condone bearing a name that celebrates a slaveholder who embraced white supremacist systems”.

It said it was acting after “a great deal of discussion” internally and with other chapters: “We strongly urge [the] National Audubon Society’s board to do the right thing and move forward with a collaborative renaming process.”

Meanwhile, the Chicago Audubon Society said last month in a letter to Elizabeth Gray, the national society’s CEO, that continuing to carry the name “does not serve us well ethically”. It said it would rename itself unilaterally within one year if the umbrella organisation did not act.

It follows similar steps by Audubon chapters in Maryland in 2021, and Seattle in July 2022.

The New York-based National Audubon Society (NAS) was founded in 1905 as a coalition of regional chapters, more than half a century after Audubon’s death in 1851. It has acknowledged his dark past, which includes slave trading, forcing slaves to accompany him on expeditions and condemnation of the abolitionist movement.

“The National Audubon Society is in the midst of a robust decision-making process about the name of the organisation,” a spokesperson told the Observer.

“This process has been informed by feedback from people across the Audubon network and beyond, research from historians about John James Audubon the person and the founding of our organisation, and analyses on the impact of the name on our mission. The board of directors started deliberations last week and will reconvene soon to continue their discussions.”

The spokesperson said the society received more than 2,300 responses to a survey it launched last year to members of its more than 450 chapters, and others less familiar with its work.

The NAS, however, has struggled to make progress, even as a national reckoning over historic racial abuses gathered pace since Floyd’s murder in Minneapolis, including local authorities ridding themselves of Confederate-era statues and monuments, and the government renaming military bases with connotations to racism.

Other prominent environmental groups acted quickly. In 2020, the Sierra Club denounced the racism of its founder, John Muir, and other early leaders; In October 2021, the Audubon Naturalist Society, which is not affiliated with the NAS, said it would rebrand itself, emerging one year later under the new name Nature Forward.

During that time, the NAS became embroiled in turbulence, with the abrupt departure of former chief executive David Yarnold in 2021 following an independent workplace report that found a “culture of retaliation, fear and antagonism towards women and people of colour”.

The society also saw the resignations of three successive executives responsible for equity, diversity and inclusion. The most recent, Andrés Villalon, told colleagues in an exit email in December that Audubon had failed to live up to its declared values of “equity, diversity, inclusion, belonging, anti-racism and a justice-oriented outlook”, according to E&E News.

J Drew Lanham, professor of wildlife at Clemson University, and a former Audubon board member who has written about the society’s wrestling with the racist legacy of its namesake, said the issue ran deeper than just forging a new identity for the organisation.

“I’ve always been in favour of a name change as long as it reflects substantive mission and action change. Names changing without hearts and minds doing the same is just lip service,” he said.

“Branding isn’t just a billboard others might see, it’s a heartbeat that should be felt. The question is does NAS just want to be seen as a brand, or do they want to be heartfelt? Be a name or be about something more.”