I am reading *The Last of the Mohicans*.
A group gets lost on their way to Fort Edward.
Then they meet Hawkeye the scout, who accuses their guide of misleading them.
Hawkeye believes the guide's heritage confirms this 
[when he says](http://books.google.com/books?id=-Hw6AQAAMAAJ&pg=PA40&lpg=PA40&dq=%22nor+do+I+care+by+whom+they+are+adopted%22&source=bl&ots=Hj0Rw7jvpf&sig=heSnZElriuCwHNo9Ps-VlHE81nM&hl=en&sa=X&ei=4ScnU9HGOYisyAHByYGYCA&ved=0CDEQ6AEwAQ#v=onepage&q=%22nor%20do%20I%20care%20by%20whom%20they%20are%20adopted%22&f=false):

> 
> "A Huron!" repeated the sturdy scout, once more shaking his head in open
>  distrust; "they are a thievish race, nor do I care by whom they are adopted;
>  you can never make anything of them but **skulks** and vagabonds. Since you
>  trusted yourself to the care of one of that nation, I only wonder that you
>  have not fallen in with more."
> 
> 
> 

I cannot find a definition of *skull* to match this usage.
A definition I've found in dictionaries that is closer to Hawkeye's intent than
the common meaning of "bone of the head" is this one from
[MacMillan Dictionary](http://www.macmillandictionary.com/us/dictionary/american/skull):

> 
> INFORMAL a person's head, or their mind
> 
> 
> 

Especially if used in this derogatory sense cited from 
[CED](http://dictionary.reference.com/browse/skull):

> 
> *derogatory often* the head regarded as the mind or intelligence:
>  *to have a dense skull*
> 
> 
> 

Hawkeye is not shy with his criticisms of this tribe.
In the above passage alone he accuses them of thievery, aimlessness, and treachery.
It is possible that by using *skulls* he is insulting their intelligence too.
But this argument seems weak to me, because the traps and ambushes Hawkeye fears the guide leading the group into require some sophistication to execute.

A supposition I think has more merit is that this *skull* is related to *skulduggery*,
which [MW](http://www.merriam-webster.com/dictionary/skulduggery) defines as

> 
> underhanded or unscrupulous behavior; *also*: a devious device or trick
> 
> 
> 

The [*skul*](http://www.etymonline.com/index.php?term=skulduggery) in *skulduggery*
("apparently an alteration of Scottish *sculdudrie* 'adultery' (1713),
*sculduddery* 'bawdry, obscenity' (1821), a euphemism of uncertain origin")
appears to have a different etymology than the bone-related
[*skull*](http://www.etymonline.com/index.php?term=skull) 
("probably from Old Norse *skalli* 'a bald head, skull,'...").
But I cannot find any sources to confirm the connection of Hawkeye's use of *skulls* to this *skul*.

What does Hawkeye mean by calling the tribe "skulls"?

**Edit**: As Leon Conrad points out below, I misquoted the Google book I cited. The correct word is *skulks*. (I have changed it above.) I have e-mailed the source I read from about the typo.