My question is do Hawks have natural predators besides humans?
Yes and no. Larger raptors rarely will prey upon hawks (very uncommon but it does happen that an eagle will take a hawk). Peregrine falcons have been known to kill hawks that are in their nesting territory (peregrines pose extremely little threat to poultry). Owls have been known to occasionally prey upon hawks (especially great horned owls, which are very powerful raptors). When eating their kill on the ground, land predators such as foxes, coyotes, etc, will take a hawk if they can do so with minimal risk.
Other birds have been known to kill young hawks and/or take eggs, such as ravens and crows.
So, not much preys on them, though it might happen more commonly than we observe. You are probably wondering what keeps them in check, then?
The answer is simple: hawks have an extremely high mortality rate in their first year of life due to starvation. I know you are probably laughing and thinking, the hawks taking my chickens are not starving! But those are probably adult and established hunters. The mortality rate of most hawks in their first year is 80-85%... that means that on average, 80-85% of baby hawks will never make it to maturity. Hunting is hard for them, they are clumsy and inexperienced, and most of their hunts end poorly. Obviously mortality rates are lower in areas with a high density of prey-- depending on the species, this means that hawks raised in areas where there are an abundance of mice, rats, and other small mammals will have a higher chance of reaching adulthood. Hard winters, drought, etc... all have impacts.
Then there is man; a lot of hawks are illegally shot of course. Some are shot with permits by government official culling programs. Believe it or not-- a lot of hawks meet their demise from motor vehicle impacts. Raptor centers and rehabbers yearly get many, many birds that are injured this way. Most do not survive. One center I talked to said that more than 75% of the dead and injured birds they receive are just from motor vehicle impacts.