Your text is so long that I think it might put people off, this is the essence of your question: In a nutshell, the addition of a definite article in this specific case can materially alter the original meaning. The experts of the Zoo refers to all the experts there, while at the same time, experts of the Zoo refers to an uncertain number of experts there. It can be all the experts, or just some of them.
Did the writer simply follow the rule that requires people not to use the definite article in front of a common noun when it's mentioned for the first time in the context?
If that was the case, I guess it will not be counted as ungrammatical for me to simply add a definite article in front of the word experts. The reason being that readers will know that it refers to none other than those very people working in that zoo, with or without a definite article there.
Then, a second thought of the issue brought to me a different understanding that leads to the opposite answer.
The definite article acts as some sort of symbol to indicate that the readers or listeners are thought to be aware of what the noun refers to. Because of this, people are allowed to break the rule aforementioned, when the noun in question is understood by most people to refer to a certain thing. People are therefore allowed to write the sun, whenever the star is mentioned.
On the other hand, mentioning a noun, without the using of a definite article in front it, shows the readers or listeners are thought not to know or be able to work out what the noun in question exactly refers to, at the precise moment the noun in question is read or heard.
Having said that, the usage of a definite article may not be proper in the quoted sentence. It may seem clear that people will know this concerns people who are specialists in this area and work in that zoo, to begin with. Things are quite definite in this sense. However, if a reader happens to be a journalist and want to interview the experts involved so as to finish a report, this reader will probably have a rather different opinion as to the certainty of this issue. The London Zoo is very likely a huge place and probably hires more than one animal expert. Have all the experts working there been involved in that event? If not, how many of them have been involved then? As shown in the article, these questions are not addressed. Since the definite article, if put here in front the word experts, conveys, or rather, implies that all the experts with the necessary knowledge have been involved, only when this is the case, people are able to declare that they know for sure whom the experts actually refers to. Otherwise, how on earth can the readers or listers, who are only ordinary people, get to know how many experts have been involved? They obviously can achive so, by simply reading the article from which the sentence quoted is quoted.
The article is written from a reporter's point of view, despite the fact that it's actually not a report. In general, reporters research and interview bofore they write. Based on this, I assume that the writer omitted the definite article here on purpose. It shows he, when writing the article, didn't know himself the exact number of experts involved and considered the addition of a definite article misleading and inappropriate.
In a nutshell, the addition of a definite article in this specific case can materially alter the original meaning. The experts of the Zoo refers to all the experts there, while at the same time, experts of the Zoo refers to an uncertain number of experts there. It can be all the experts, or just some of them.
So here I am, stuck in the middle of this question. I would like to hear your opinions on this matter.
You have answered it yourself.
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