Interpretation of Results
In response to the primary research question of this project, and based on the results in the first level of analysis, artificial light does seem to have some implications for the detection of common nighthawk vocalizations. Though, it appears that the level of significance of this effect may contextual, depending on other habitat factors such as latitude. No significant increase in nighthawk detection was observed in artificial light that could not be explained by natural diel patterns. Though, it is worthy mentioning that the highest period of relative increase between light and dark habitats was during the civil twilight, which constitutes the common nighthawk's natural foraging period. Though it may not be statistically significant, this finding does provide support for the assumption that common nighthawks may utilize artificially illuminated habitats specifically for obtaining insectivorous prey. Interestingly, nighthawk activity extended into nautical twilight regardless of light treatment, implying that there could be an alternative explanation for this change in behavior. Further research into the effects of artificial light on common nighthawk foraging at lower latitudes where the twilight periods are shorter, and darker periods more pronounced, could confirm its significance in this respect.
What this project did confirm is that the presence of artificial lighting had no effect on the detection rates of territorial wing booms, indicating that it does not impact nesting habitat selection. It is conceivable that nighthawks simply vocalize much more often than they produce wing booms. However, consistently higher vocalization detection rates compared to wing booms may indicate that common nighthawks are traveling a measurable distance from their nesting sites to take advantage of abundant prey. While nighthawk territories range considerably from 1.5 to 28 ha, they are known to travel up to 6 km to obtain resources necessary for survival (Ng, 2009; Brigham et al., 2020). Competitive exclusion could provide a reason for the need for extensive travel to partake in foraging behavior. Another theory suggests that nighthawks choose to nest away from anthropogenic sources of light to avoid predation. Whether source, sink, or benign habitat, the reason for the observed variation between vocalization and wing boom detection rates is worth of further investigation.
Several weaknesses were revealed in the design of this research project. Namely, a lack of randomization of treatment sites across varying latitudes, which may effect the timing and duration of twilight periods. This was largely due to the availability of existing data. Another weakness of the study was a low number of replicates per station x time period, particularly at the third level of analysis. A cursory overview of the vocalization data at this level suggests that the use of artificial light may enable nighthawks to override their natural bimodal pattern of activity that is typically limited by the timing of natural lighting. However, considerable variation due to low survey effort and overfitting of the model prevented the confirmation of these trends. To avoid this in the future, it is recommended that sun periods in the morning and evening are each considered as individual variables (instead of two combined factors of sun period and am/pm) as well as obtaining more extensive data. As the use of autonomic recording devices proliferates and the efficiency of automated vocalization detection software progresses, a more comprehensive study addressing the intensity of common nighthawk foraging under artificial light may still reveal some level of influence.
What this project did confirm is that the presence of artificial lighting had no effect on the detection rates of territorial wing booms, indicating that it does not impact nesting habitat selection. It is conceivable that nighthawks simply vocalize much more often than they produce wing booms. However, consistently higher vocalization detection rates compared to wing booms may indicate that common nighthawks are traveling a measurable distance from their nesting sites to take advantage of abundant prey. While nighthawk territories range considerably from 1.5 to 28 ha, they are known to travel up to 6 km to obtain resources necessary for survival (Ng, 2009; Brigham et al., 2020). Competitive exclusion could provide a reason for the need for extensive travel to partake in foraging behavior. Another theory suggests that nighthawks choose to nest away from anthropogenic sources of light to avoid predation. Whether source, sink, or benign habitat, the reason for the observed variation between vocalization and wing boom detection rates is worth of further investigation.
Several weaknesses were revealed in the design of this research project. Namely, a lack of randomization of treatment sites across varying latitudes, which may effect the timing and duration of twilight periods. This was largely due to the availability of existing data. Another weakness of the study was a low number of replicates per station x time period, particularly at the third level of analysis. A cursory overview of the vocalization data at this level suggests that the use of artificial light may enable nighthawks to override their natural bimodal pattern of activity that is typically limited by the timing of natural lighting. However, considerable variation due to low survey effort and overfitting of the model prevented the confirmation of these trends. To avoid this in the future, it is recommended that sun periods in the morning and evening are each considered as individual variables (instead of two combined factors of sun period and am/pm) as well as obtaining more extensive data. As the use of autonomic recording devices proliferates and the efficiency of automated vocalization detection software progresses, a more comprehensive study addressing the intensity of common nighthawk foraging under artificial light may still reveal some level of influence.
Implications of Findings
The results of this project do not provide sufficient support for wide-scale illumination of habitat in efforts to curb the decline of common nighthawk populations. Yet, they do not rule out the possibility of the role of artificial light in supporting the survival of existing populations, particularly in latitudes where the temporal opportunity for obtaining food resources is limited. Ultimately, the lack of strikingly significant effects of artificial light on common nighthawk activity does lend confidence to the conclusion that other factors, such as nesting habitat loss and degradation, are likely to have a larger role in population declines. It is recommend that further research is conducted, considering the above recommendations, whilst predominantly focusing on preserving and restoring nesting habitat for an efficient recovery of the species.