Hi, Egyptian 2017,
A pair of sparrows ( has - have ) built a nest in the tree since last week .
Both are grammatically correct. In Egypt, we follow the singular form.
BTW, this question has been discussed a long time ago one the G.E. Here is its link:
1. Merriam-Webster's Dictionary of English Usage (1994) states:
"Pair is one of those collective nouns that take a singular or plural verb according to notional agreement. If you are thinking of the individuals in the pair, you will use a plural verb"
2. With the noun "birds," however, the results on Google are about 50-50. Google examples:
- ”When a pair of birds are placed together they stay for life together for breeding."
- ”This second pair of birds has reared three young, having been established in their cliff top home by Operation Chough, at Paradise Park in Hayle."