Hello Molly,
     Haven't found 1871 Census for David so far.
       1881 Wales Census. Brecknock, Llywel, Breconshire.
     David  Nicol  32  Shepherd  b *? Scotland. (*Kinross-shire. Hard to read & not transcribed) 
     Jane      "     29                 b Perthshire, Scotland.  
     Margaret Davidson Nicol  8   b Transcribed as Brecknock, Llywel but this is scored out & 
                                             Kinross-shire written above. Again, difficult to read.
     Mary Jane Ballingall Nicol 5   b Brecknock, Llywel, Breconshire, Wales.
     William  Nicol                 3   b  Brecknock.
     Elizabeth Maria Nicol 11mons b Brecknock.
     This may be his marriage to Jane: David Nicol & Jane Davidson 1873 at Orwell, Kinross-shire.  I suspect daughter Margaret is the Margaret Davidson born to Jane Davidson 15th March 1873 at Orwell, Kinross-shire. (F.Search)
     Mary Jane B Nicoll, birth registered Jul-Sep 1875 at Brecknock, Brecknockshire.
     Elizabeth Maria Nicoll, birth registered Apr-Jun 1880 at Brecknock.
     
       1891. Arngask, Fife. (The one Annie mentions in an earlier post)
     David  Nicol  43  b  Orwell, Kinross-shire. Shepherd.
     Margaret  "   40  b  Portmoak,    "
     William    "   13  b  England?
     Elizabeth Maria Nicol 11 b England?
     Melville Litster Nicol    1 b Auchtermuchty, Fife.
    Not found a death for Jane Nicol so perhaps she died in Wales.
    May be his 2nd marriage: David Nicol & Margaret Litster 1887 Portmoak, Kinross-shire.
       1901. Forteviot, Perthshire.
     David  Nicol  52  b  Orwell, Kinross-shire. Shepherd.
     Margret  "     50  b  Portmoak,   "
     Melville  "     11  b  Auchtermuchty, Fife.
     
               Regards,     Dod.
                                             
PS.   1871. Halteasses House, Ceres, Fife.
     David Nicol  22  Lodger b  Orwell, Kinross-shire. Shepherd.
     Lodging with Thomas Davidson (Ag Lab) & his wife Helen Kassell.