The Uluguru Mountains form a component block of the Eastern Arc Mountains of Tanzania and Kenya and are known for a high degree of endemic vertebrate and plant taxa. Among the Eastern Arc Mountains, the Uluguru Mountains rank second in the number of endemic species. Although the forests in these mountains have received considerable ornithological attention, studies on how forest bird communities in the available low elevation forests are affected by seasons remain patchy and sporadic. Such studies are important because in the Uluguru Mountains, forest destruction in the lower slopes has been severe to an extent that there is very little substantial forest survives below 900 m above sea level. Using mist netting, seasonal variation in understorey bird communities in the remaining low elevation forests in the Uluguru Nature Reserve was assessed between 2005 and 2011. Species diversity and relative abundance of the birds were higher during the cold season in comparison with the hot season possibly due to seasonal elevational movements of some species. Elevational migrants made a large proportion of the avifauna in the study area. The results suggest that low altitude forests are important cold season refugia of elevational migrants and these forests need continual protection