Because the oceans are subject to harsher conditions like winds and waves, most coastal and ocean birds have to be strong fliers.
(the oceans; are; subject to harsher conditions like winds and waves) (most coastal and ocean birds; to be; strong fliers) (the oceans; are subject to; harsher conditions)
the oceans most coastal and ocean birds the oceans
are to be are subject to
subject to harsher conditions like winds and waves
strong fliers
harsher conditions