In Harry Potter, the sentence
I'll send this with Hedwig when she gets back; she's off hunting at the moment.
is translated as
Ich schick dir diesen Brief mit Hedwig, sobald sie zurückkommt, im Augenblick ist sie jagen.
What type of construction is "im Augenblick ist sie jagen"?
It is not present tense -- that would be "im Augenblick jagt sie"
It's not a noun phrase either -- that would be something like "im Augenblick ist sie zum Jagen".
Is this construction at all correct?
As for the intention of this particular wording (assumed of course):
Im Augenblick jagt sie would be
She's hunting right now or At the moment, she is hunting,
focussing on what she is doing.
The wordings used (in both english and german texts) however want to convey that Hedwig is not present. The reasons for her absence is a side information, which makes the sentence seem more complete and preemtively answers the question "where is she then?".
Carsten Schultz's suggested link Absentiv is worth reading.
It explains the construction and usage of these sentences quite well,
along with the reasons they exist.
