warning In fun(...) : no DISPLAY variable so Tk is not available

I am getting the above warning following loading of Geneland 3.1.5 on 
unix , while a simple plot sends output to the pdf file ( see attached 
code) no output results from Geneland functions, resulting in empty pdf 
files
  

 > library (Geneland)

Loading required package: RandomFields
Loading required package: fields
Loading required package: spam
Package 'spam' is loaded. Spam version 0.21-0 (2010-03-13).
Type demo( spam) for some demos, help( Spam) for an overview
of this package.
Help for individual functions is optained by adding the
suffix '.spam' to the function name, e.g. 'help(chol.spam)'.

Attaching package: 'spam'

The following object(s) are masked from 'package:base':

     backsolve, forwardsolve, norm

  Try help(fields) for an overview of this library
fields web: http://www.image.ucar.edu/Software/Fields
Loading required package: mapproj
Loading required package: maps
Loading required package: snow
Loading required package: tcltk
Loading Tcl/Tk interface ... done
ooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo
o        Geneland is loaded                                       o
o                                                                 o
o                * Please *                                       o
o                                                                 o
o        Register on                                              o
o        http://folk.uio.no/gillesg/Geneland/register.php         o
o                                                                 o
o        See manual on                                            o
o        http://folk.uio.no/gillesg/Geneland/Geneland.html        o
o                                                                 o
o        This is Geneland-3.1.5                                   o
o                                                                 o
ooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo
Warning message:
In fun(...) : no DISPLAY variable so Tk is not available

 > pdf("test.pdf")
 > plot(1:10,1:10)
 > dev.off()

null device