The warbleR function lspec produces image files with spectrograms of whole recordings split into multiple rows. For a long recording several image files will be produced, which could be inconvenient when dealing with many long recordings. I recently added a new function lspec2pdf that combines lspec images in .jpeg format into a single pdf file (available in warbleR 1.1.5 or higher).
You need warbleR version 1.1.5 or higher to be able to run the code (currently you have to download it from github using the package devtools).
Download a couple of long recordings (> 2 min) from xeno-canto and convert them to .wav format
Create the long spectrograms in .jpeg format
And the last step is to create a single pdf file for each sound file. Note that the keep.jpeg argument allows to remove the .jpeg files (when set to FALSE)
You should get 2 pdf files that look like this one