Estrus detection in heifers is pivotal for reproductive success. The objective of this study was to identify behaviors associated with 2 different periods of the estrous cycle of Holstein heifers. Eighteen heifers at breeding age were selected, balanced by age, BW, and BCS (average 13.7 ± 1 mo, 394 ± 32 kg, and 3.43 ± 0.1 respectively), and observed for 6 wk. The experimental period was divided into 3 periods of 14 d each. All heifers received the same basal diet to meet requirements (NRC 2001), fed once daily. Visual observations were performed in 30 min segments every 2 h from 6AM to 6PM. Video recordings were used to confirm observations. Twelve behaviors were recorded (Social Lick, Rump Lick, Tail Paint Lick, Body Butt, Head Butt, Push, Chin Rest, Anogenital Sniff, Play Rub, Winner, Mount, and Attempt Mount). A synchronization protocol starting on d 1 of each period (Ovsynch: 100mg GnRH at d 1, 25mg PGF2α at d 7, and 48 h later an application of 100mg of GnRH) was used to stimulate periods of high and low interactions. Observations were summarized to daily counts of interactions for each behavior. Ovaries were examined via ultrasound imaging on d 1, 8, and 10 of each period. The presence of follicles or a corpus luteum (CL) was recorded with their respective sizes. Lying time, standing time, and bouts /d were recorded using accelerometers (Onset HOBO Pendant G) at 1 min intervals for 14 d. Statistical analyses were performed using the GLIMMIX procedure of SAS (v9.3). During periods of low activity per the synchronization protocol, social (P < 0.01) and paint (P < 0.05) licking were more likely to be expressed than estrus-related behaviors such as rump licking (P < 0.05), chin resting (P < 0.002), and mounting (P < 0.003). The aforementioned estrus related behaviors were also performed in more frequency than other behaviors when a large follicle is present (P < 0.03). Heifers spent more time standing and less time lying per day when they had a large follicle (P < 0.006) compared with a small follicle. In conclusion, increased activity and specific behaviors may be used in the future to facilitate estrus detection in heifers.