This study was conducted to show the seasonal behavioral changes with some anatomical interpretation to the heat-exchange system. The study applied on 200 one day old broiler chicks, 100 reared in winter season (winter group), and 100 reared in summer (summer group), each group two replicates, 50 for each. The rearing period was 35 days. Chicken behaviour was recorded by visual observation at daily scan sampling 3 times /day, 10 minutes / for each replicate. The following behavioral patterns were recorded, feeding, drinking, leg and wing stretching, body scratching, preening and resting. Final body weight, total feed intake, food conversion ratio and mortality rates were measured as performance index. The arterial blood supply and venous drainage of the pelvic limbs of the chicken were demonstrated by injection of colored gum milk latex and treated by the ordinary method of preservation. Arterio-venous association was investigated in the tibial region of 10 birds in each group. The study revealed that the behaviour parameters in summer and winter are greatly significantly differed at P≤ 0.05, summer group showed higher percentage of resting behaviour 33 ±0.94 %, and higher percentage of leg and wing stretch compared with winter group. Final body weight, feed intake, were significantly differed at P≤0.05, winter group showed the highest final body weight 2093 ± 0.75 gm and in the same time lower feed intake 3532 ± 10.5 gm Compared with summer group. Increasing of resting behaviour and leg & wing stretch in broiler chicken reared in summer was explained on the basis of bird anatomy. The intermingled network of arteries and veins (rete tibiotarsale) help in thermoregulatory mechanism because exchange of heat between arteries and veins is considered to be of a great importance to Keep the bird body temperature within the normal.