With a given motor, these losses and the proportions of the losses are determined by the designer of the motor.
Essentially the core losses are dependent on the laminated core steel properties and the flux in the core. Flux is dependent on operating voltage, the number of turns in the winding and the frequency.
In essence this means that for any given motor (design), when operating at rated voltage, the core losses are fixed irrespective of load, as the iron losses are dependent on
voltage and frequency and not on the operating load.
Stray, windage and friction loss are basically fixed and are determined by the design of the motor. I2R losses in the motor for any fixed design are solely dependent on the square of the current drawn by the motor. Note the stator and rotor resistances are fixed by the design of the winding. Resistance does, however, change with temperature. Both stator and rotor currents increase or decrease with load.