MADRID, March 26 (Xinhua) -- The three pandas at the Madrid Zoo, Hau Zui Ba, Bing Xing and their daughter Chulina, have become undoubted stars at the zoo complex in the Spanish capital city of Madrid, according to the zoo's head of communications, Maria Jose Luis Cerezo.

She told Xinhua last Thursday that the pandas have become stars, because in all of Spain pandas can only be seen in Madrid.

Two giant pandas -- Bing Xing and Hua Zui Ba -- arrived at Madrid's Zoo Aquarium in September 2007, thanks to a 10-year cooperation agreement between Spain and China.

Chulina, who is now a year and a half, is the fourth panda cub born to the couple, with the first two being twins, Po and De De, who were followed by Xing Bao.

Those three are now back at the specialist panda breeding center in Chengdu City in southwest China's Sichuan Province.

"Visitors think they are adorable," said Luis Cerezo, "People love the way they sit, how they look and how they hold the bamboo that they are eating,"

Chulina had weighed only 180 grams at birth, but has grown to almost 50 kilograms, she said.

Looking after the pandas is a major task and the zoo has invested heavily in specialist wardens and their diet -- some 150 kilograms of fresh bomboo everyday.

The Madrid Zoo has had a long relationship with pandas ever since the late 1970s when King Juan Carlos and Queen Sofia were given Shao Shao and Chang Chang, who became the parents of Chulin: the first panda to be born in captivity in Europe.

The Madrid Zoo is also at the forefront of panda breeding programs.

"We work with other institutions, because it is not easy and it will be another three years until Hua Zui Ba is fertile again," said Luis Cerezo.

The relationship with the Chengdu center is vital for the Madrid Zoo as Chinese experts always give the Spanish side a lot of help, she said.

The year of 2018 is the 40th anniversary of the first arrival of Chinese giant pandas in Spain.

China and Spain have signed an agreement which allows the panda couple to stay in Madrid Zoo for another five years until 2023.