No automatic method available. Sorry. The pelican is a drawing You have traced an image which is scanned from a book, I guess. As well I guess the pelican drawing, before it went to the book, had solid lines with much less white breaks. Printing has detoriated it and your tracing as well.
How do I know their line patterns are drawn, not transformed automatically from a photo or painting?
Because the long lines seem to follow the apparent curvature of the 3D surface. No program without human knowledge can deduce 3D information having only a flat 2D image.
But the conversion? In theory an ingenious programmer could create a program which extracts the directions of the lines on the pelican as well as their local density variations. Then it would draw a new set of solid lines, maybe with with greater line spacing and line widths, but still following the original directions and local black vs white density ratio variations. I guess the line density cannot be reduced much without reducing the information value of the image radically.
I'm afraid that ingenious programmer has a good reason to stay far away from less ingenious persons like me, who have a tendecy to want something but not to start with generous money offering. If you happen to be as unpopular, prepare to redraw the pelican manually with solid lines by yourself. I guess it's not impossible. The original artist has already done it once.
I guess that the preceding story isn't exactly just the wanted one, so I suggest other way. At first try to guess a greyshade image of the pelican, the intended greyshades that the original drawing presented. Smooth the image as much as is needed to make it presentable with coarse enough engraving-like lines. That means a huge detail reduction, if you expect remarkable line sparsening. Here's my attempt in Photoshop:
Do not think it's a painting. It got at first several subsequent median filterings to close the gaps, then I selected with manually drawn paths separate areas one by one and gave to them heavy surface blur to get smooth shades. The eye was kept as own selection. Finally the brightness was reduced, only the original background area was kept white.
Then an engraving simulation filtering was applied:
As said, this is in Photoshop. The used engraving simulator is a preset in Filter Forge plugin package and my grayscale image has brightness&contrast matched for that process. Other engraving simulators need other settings.
From this older case Create engraving in GIMP/Inkscape you can find how it can be made totally in vector domain (Inkscape), if you have a greyscale photo or other bitmap image prepared for it.