Birds make use of their lower limbs for functions such as grasping, climbing, wading, digging, nest building along with many other actions. The tendon-locking mechanism (TLM) underlying the closing of digits of bird feet is essential for aspects of the avian lifestyle. A number of studies have previously investigated the mechanics of the TLM across multiples species. This project describes the forces underlying the TLM mechanism. We use properties of the flexor muscles of the leg used for grasping behaviors in related avian species, Red-tailed hawk (Buteo jamaicensis) and Cooper’s hawk (Accipiter cooperii) to address this mechanism. Using traditional dissection and muscle evaluation techniques, flexor muscles of the left leg were collected to estimate the physiological cross-sectional area (PCSA) and muscle force in Newtons. Muscles were removed at proximal and distal attachments. Pennation angles and the mass for each muscle were measured before muscles were immersed in HNO₃ to facilitate muscle fiber separation. Many fibers from each muscle were carefully arranged and photographed for data collection. Mean muscle fiber length, pennation angle, and PCSA were used to calculate forces muscles are capable of contributing to the TLM. We found that the larger Red-tailed hawk’s muscles had greater force outputs when compared to the muscles of the smaller Cooper’s hawk. A wider sampling of species is necessary in to gain a better understanding of how the forces contributing to the TLM affect the lifestyle of various species of birds.