Our method for manipulating artificial light at night, or ALAN, inside nest boxes, is powerful for determining the effects of ALAN on the behavior, physiology and fitness of animals. This technique helps overcome the challenges inherent to studying how ALAN affects free-ranging animals, because researchers can expose animals to light at night in a controlled fashion. This system can be used in any avian or mammalian species that uses cavities for breeding or resting, and also has the potential to be modified for use in other contexts.
Start by habituating the animals to the experimental setup by placing a dummy box on the top of the nest box at least one day prior to the experiment, to minimize the effects of novelty aversion. To survey the focal individuals, fit the animals in the study population with a passive integrative transponder or PIT tag, to allow for identification within the nest box, without disturbing the birds. In experiments involving the effect of artificial light at night or ALAN on sleep behavior, visit the nest boxes on the night before the experiment, and scan the boxes with a radio frequency indication or RFID reader, to determine which birds are roosting inside.
To record undisturbed sleep in the absence of ALAN, implement a repeated measures design by recording sleeping under conditions of darkness for one night, and then in the presence of ALAN, for one night. For both nights, before taking the infrared, or IR camera into the field, synchronize the time with the local time. Next, insert an MDSD card into the SD slot into the mini DVR recorder adjacent to the battery.
At least two hours prior to the onset of darkness, remove the dummy box from the top of the nest box and open the nest box lid to place the plate containing the IR camera inside, with the camera objective oriented downward. Then extend the electronic connectors out of the groove in the nest box. After closing the nest box lid, place the enclosure containing the battery, recorder and timer, on top of the nest box.
Then connect the red connector from the recorder to the white connector from the camera, the yellow connector from the recorder to the yellow connector from the camera, and the black connector from the battery to the red connector from the camera. And for the ALAN night, the LEDs to the timer, and the timer to the power source. Once connected, put the wires inside the enclosures that houses the system.
As the recording starts, check with a small TFT screen to ensure the correct image, and then press record. One hour after dark, return to the nest box to check the identity of the birds sleeping inside, by moving an RFID transponder reader around the bottom and sides of the nest box, and recording the unique identification number communicated from the PIT tag. On the morning following the control recording, two hours after sunrise, collect the battery system from the nest box before returning the dummy box on top of the nest box.
In the laboratory, charge the battery and remove and download the SD card from the recorder to collect the behavioral data. After successfully downloading the data, erase the data from the SD card, followed by inserting the card into the mini DVR recorder. On a subsequent night, implement the light exposure treatment by setting up the timer system for the desired time of light exposure, and control recording as described before, with the timer connected to the power and the LEDs connected to the timer.
For experiments involving multiple nights of light exposure and video recording, collect the systems each morning to recharge the batteries during the day, and then replace the system in the evening. Later, collect data on the response variables of interest. The study documented the dramatic effects of ALAN exposure on the sleep behavior.
The birds exposed to ALAN at a relatively low intensity of 1.6 lux, woke up half an hour earlier, left the nest box 20 minutes earlier, and slept 40 minutes less than the control birds. Here we focus on using the system to assess effects on sleep, but the system can also be used to test effects on developing nestlings during the breeding season. To assess the physiological effects of ALAN exposure, animals can be captured, blood samples obtained, and morphometric measurements can also be taken at this time.
This nest box based system has allowed researchers to assess a range of intriguing questions regarding biological effects of ALAN, that could not previously be assessed, such as effects on sleep.
