@article {Pebesma2005Environmetrics,
	title = {{Mapping sea bird densities over the North Sea: spatially aggregated estimates and temporal changes}},
	journal = {Environmetrics},
	volume = {16},
	number = {6},
	year = {2005},
	pages = {573-587},
	author = {Pebesma, E.~J. and Duin, R.~N.~M. and Burrough, P.~A.}
}