Relationship Between Birds Arriving at Roost and Illumination Levels

Relationship between birds arriving at roost and illumination levels.

Differences in numbers and species of birds arriving at roost seem to be determined by the levels of light present at dusk. A light meter was used to check the illumination level at time of first arrival of birds and at five-minute intervals afterward. Binoculars were used, while light permitted, to determine the different species of birds and the quantity as they arrived into the roosting and pre-roosting areas. This study was conducted between 5:20pm and 6:05pm. The temperature ranged from the low fifties to the mid forties; wind was moderate with small gusts. The European Starling was the first to arrive into the roosting and pre-roosting areas, only coming in small groups and leaving quickly. The American Robin started arriving around 5:30, illumination at 1262 foot-candles, in small groups and stayed for a while. As the sun continued to set and light levels continued to decrease, the starlings arrived more consistently coming in and preparing for the evening roost. The robins dissipated as more starlings arrived. It appears that robins do not prefer to take roost in the presence of starlings. It also appears that the starlings prefer to begin their overnight roost at the lowest levels of light, possibly due to being more susceptible to predatory attacks, e.g.: at 6:00pm, the smaller roosting area on the south side of the subject area was "tested" as a hawk, possibly red-tailed, swooped in and found an unprotected starling to consume.