"While it is reasonable to assume that many have died that were not counted, 20,000 has to be a gross exaggeration which is (creating) an atmosphere of fear,'' he said.
The oil spill in the Gulf of Mexico killed 3800 seabirds and the assertion that 1000 times more birds in New Zealand could die from offshore oil drilling _ 20 million _ was wrong, he said.
Other complainants shared similar views.
In response, Greenpeace said the National Oiled Wildlife Response Centre reported more than 2000 birds had died as a direct result of the spill.
The estimated figure of 20,000 birds was based on British and American research which found the number of bird carcasses recovered after oil spills represented only about 10 per cent of actual deaths.
It then explained the statement that a deep sea oil spill could be more than 1000 times worse than the Rena spill was made in the context of general environmental impact, and not specifically in relation to loss of seabirds.
"In our view this is also how the general viewer will have understood the statement.''
An authority report released this week said the claim that 20,000 birds were killed was very strong and was a long bow to draw, particularly when the practise was based on British and American research.
It found the claim the spill had killed more than 20,000 birds was likely to mislead and deceive consumers and upheld the complaint.
However, it did not uphold the second complaint about a deep sea spill being 1000 times worse because the use of the word "could'' presented the claim as an opinion or possibility as opposed to absolute fact.
Mr Leyland today said he was "moderately'' pleased with the outcome, but disappointed the second complaint was not upheld.
"I think the claim that 20 million birds could die was the most ridiculous of the claims.''
Greenpeace said it accepted the finding but stood by the ``scientific estimate'' 20,000 birds could have died.
"Greenpeace will ensure any future media advertising reflect the findings,'' it said.
"The primary intention of the oily penguin TV advertisement was to highlight how much worse a deep sea oil spill could be in terms of its impacts on New Zealand's oceans, coastlines and wildlife.
"In the context of New Zealand's coastal waters being opened up to deep sea oil drilling, the statement that a deep sea oil spill could be 1000 times worse than the Rena (which was regarded as consistent with ASA guidelines) is at the heart of the position that Greenpeace wished to convey in the advertisement.''
