A Berlin historian is combing through thousands of names to identify members made to sell their shares back to the zoo at a loss under the Third Reich, and has begun tracking down their descendants ahead of publishing her findings.
"Jews were very important for the zoo," said historian Monika Schmidt, who estimates up to a quarter of the zoo's 4,000 shareholders in the 1930s were Jewish.
"But they were pushed out step by step by the zoo itself, before the Nazi state asked any institution to do those things," Schmidt told AFP.
Zoo shareholders did not receive dividends, but their families enjoyed free entry and the prestige of supporting an important social institution.
Their exclusion is just one example of how Jews were pushed out of public life in 1930s Germany and stripped of their assets.
"Today, the zoo is just a zoo, with animals to watch," said Schmidt, with the Center for Research on Anti-Semitism in Berlin.
"But in former times, the zoo was a very important meeting place for the city."
As part of her research Schmidt found Jochanan Asriel, 89, whose grandfather was a shareholder.
As a boy, Asriel lived close enough to ride his bike to the zoo's playground.
"I went there every day in the afternoon, and there was a big coffee house in the open, where they served beer," Asriel told AFP by phone. "Every day there was another orchestra playing."
Asriel fled Germany as a teenager in 1939 and now lives in Haifa, Israel.
"I remember all the animals, and I remember where they were placed," Asriel said.
"I don't remember what I ate yesterday, but what I remember from the zoo, I remember very well."
Asriel said he visited the zoo offices some 20 years ago to find out what happened to his grandfather's share, and saw that it changed ownership under the Third Reich.
In 1938, Jewish shareholders were forced to sell their shares back to the zoo for less than their value, according to Schmidt.
The zoo, in turn, re-sold the stocks to "Aryanize" the institution.
Now, Schmidt is poring over names in a post-war recreation of a shareholders' log, and will compare them to residence and restitution records in an attempt to identify former Jewish patrons.
Commissioned by the zoo, she plans to publish the names and biographies in a book next year.
Reparation payments not being considered
The zoo's actions pale in comparison to other atrocities committed in Hitler's Germany, but historians say there is value in documenting them.
"It's very important to see that this discrimination and these Nazi crimes were not only done by some people, but in all parts of society," said Johannes Tuchel, a professor of political science at the Free University of Berlin.
Just as the revelation last month of a vast trove of hidden Nazi-looted art in Munich showed, there is hardly a chapter of the Third Reich that can be considered closed.
The zoo's undertaking is what Tuchel calls a "third wave" of research that started around the 2000s in Germany.
After some Nazi war crimes were prosecuted and reparations paid out, attention turned to returning confiscated artwork, and how public institutions treated Jews during the Third Reich.
"The Department of Justice, the Foreign Office in Germany, and so on, gave jobs to researchers and said 'OK, tell us a story, what happened in our institution in the Nazi period'," Tuchel said. "New generations are coming and want to know what happened."
The zoo's Nazi-era past received little public attention until 2000, when retired New York sociology professor Werner Cohn wrote in asking about his father's shares.
He published the response online, including a letter from a zoo lawyer stating there was "neither force, nor compulsion" in the transfer of shares from Jews to non-Jews.
This garnered attention from German media and prompted a first zoo-commissioned study by Schmidt, which revealed the stock sales, removal of Jewish board members, and the barring of Jewish visitors from the zoo starting in 1939.
In 2011, the zoo installed a commemorative plaque for Jewish shareholders.
Now, they want to do more.
"It is important to make the decision to continue to engage with this topic, to not forget what is possible," said zoo spokeswoman Claudia Bienek, noting the particular importance of documenting the lives of former Jewish shareholders in a book.
Bienek said reparation payments are not being considered.
Cohn, 87, has refused to visit the commemorative plaque, in part because the Berlin Zoo did not pay reparations to an Israeli zoo as he had suggested.
"If they had done that, even in the small scale, symbolically, I would have felt much better about it," Cohn told AFP. "But they said no, we'll give you a plaque. A plaque."