The more acceptable description is:
a) The indian roller is on the window ledge
I think while deciding on which of the two options are more appropriate we subconciously consider the fuctionality of the scene. Thus although both the onstructs are grammatically fine, we prefer th first one as it bewtter describes the functional aspect of the scene where an indian roller is sitting on the ledge. That is we try to focus more on the fact that the indian roller had the option to do a lot of other things or be at a lot of other positions with respect to the ledge so the unique position/function it is displaying in the picture is of importance wheras the ledge was only a secondary contributer to the function as it is inanimate and immobile and hence cannot directly be responsible for the function. Thus we tend to choose the active agent as the figure while describing a scene and denote all other passive elements as parts of th e background.
Test Case 1
BACKGROUND: Language spoken in 1st 5 years : Hindi Stayed at for 1st 5 years: Nagpur Parents' mother tongue : Hindi Schooling in Hindi till : Class 10 gayA chalA paRA DaalA uThA nikal Y N Y N N keh Y N N Y N bol N N Y Y Y ro N N Y N Y has N N Y N Y e.g of usage of different LVs: Main kamre se nikal gaya. Ma ke chillane pe main ro para. Uski baatein sunke main has utha. Baccha bhook se ro utha.
Test Case 2:
BACKGROUND: Language spoken in 1st 5 years : Hindi Stayed at for 1st 5 years: Bareilly Parents' mother tongue : Hindi Schooling in Hindi till : Class 10 gayA chalA paRA DaalA uThA nikal Y N Y N N keh Y N N Y Y bol Y N Y Y Y ro Y N Y N Y has Y N Y N Y e.g of usage of different LVs: Woh yahan se nikal gaya Meri baat sunke woh roh para Ye sunke woh ro utha
While using the LV "utha" there seems to be the implication of a sudden change in energy, as if the correspondin HV suddenly happens disturbing an existing state of calmness.