Ver los pájaros, Ver a los pájaros
Once again a Duolingo question:
They gave me this sentence to translate (I do not remember if I was set to learning English from Spanish or learning Spanish from English, but I think the first):
I was looking at the birds through the window all day on Sunday.
I put:
estuve viendo los pájaros por la ventana todo el día el domingo
I was corrected to:
Estuve viendo a los pájaros por la ventana todo el día el domingo.
The given answer:
El domingo estuve viendo a los pájaros por la ventana todo el día.
(I do like El domingo better at the start, but it is risky in Duolingo to alter word order)
My question is not the use of the progressive, if progressive is used in one sentence it is best to put it the other in Duolingo, whether it was what one say or not (I probably would have said “vi” instead of “estuve viendo” unless I had some really good reason I wanted to emphasize the action. But that is a guaranteed fail on Duolingo.
My question is:
The “a” here is as far as I can see a personal “a” associated with a direct object.
Vi mi coche por la ventana.
Vi a mi perro por la ventana.
I don’t see the birds that swarm my house as needing a personal “a”, even though I built bird houses and picked specific plants to accommodate them. I can see some might, so I am not saying the personal “a” is wrong, I just don’t see it as being required.
Is the "a" needed and if it is optional, is it more common to use it, or not?
4 Answers
As a native Spanish speaker I wouldn't use the "a" even if "viendo" is used in the sense of "mirando".
Anyway I have to say that "ver los pájaros" sounds rather general while "mirar a los pájaros" sounds intentional, centred in the birds behaviour and something that caught your whole attention. You can take this as a rule, not only for this instance. But remember that "estuve mirando las flores con gran detalle" (because there isn't a behaviour to look in flowers)
ETA: Some extra examples: "Estuve viendo los pájaros por la ventana"; but "estuve viendo a un par de pájaros construyendo su nido" ("ver" is meant as "observar" here). This is an example of how the "a" appears once some kind of behaviour is part of the picture. In everyday talk we may add an "a" to the first phrase and drop the "a" from the second one without it changing much. We may even not notice it.
Como español yo diría:
"Estuve todo el domingo viendo los pájaros por la ventana" but you can use "mirar or observar" too. We use "a" for some sentences but not always, sometimes the article "a" give sense to a sentence
As a native Spanish speaker I wouldn't use the "a" even if "viendo" is used in the sense of "mirando".
Pues ya somos tres hispanoparlantes, dos de Madrid, que lo hace más seguro 
, jeje, Alec, no te lo tomes en serio 
, que dicen lo mismo: sin "a".
Para mí es igual ver un coche, ver un perro, ver los pájaros.
Hola Bosque.
I'll use Nkm's trick and offer a couple of links.
The first is a similar question I asked recently regarding the same DL sentence:
"Ver" or "Ver a" for "To look at." Is the "a" a personal "a"?
The second is the discussion page for the sentence itself, where I've tried (apparently without much success) to share the info provided by Julian and Asto.
"El domingo estuve viendo a los pájaros por la ventana todo el día."
