Snow petrels (Pagodroma nivea) are birds breeding in crevices on the Antarctic Peninsula. We develop a system to monitor the nest temperatures and times birds spend outside their nests. To estimate this time, the system has been equipped with a simple Light Dependent Resistor (LDR) to overcome the insensitivity and false positives generated by Passive Infrared (PIR) motion detectors in the presence of fast moving and heat insulated birds. The system consists of a Arduino Mini Pro (3.3V, 8MHz), an RTC (DS3231N) providing a sufficiently accurate time and a micro SD card in which all measurements are stored. To maximize power efficiency, on-board calculations are avoided. The main design challenge is to maximize the uninterrupted availability of the system without exceeding the permissible size limit. The expected subzero temperatures of around -20 degrees Celsius prohibit the use of LiIon batteries which operate at 60% of their normal capacity in these harsh environments. Hence each system is powered by a 9V Alkaline block battery. The power consumption is 0.67mAh while the ADC samples the LDR resistance at a rate of 4Hz. It spikes to 40mAh if the SD card is accessed every 3.5 minutes to dump the measured values. Nevertheless a 9V battery is expected to power the system for a minimum of 14 days continuously.