The authors of this paper recognized a lack of literature on the indirect effect predators have on prey, and pondered that this perceived risk might have a greater influence on prey behavior and life history than direct predation. By consistently removing any possibility for potential predators to reach the nests of a population of song sparrows, as well as playing recordings of potential predators, the authors reported a 40% decrease in the number of offspring produced. They also report a stronger effect on the proportion of nestlings expiring in the second brood, which may allude to the predator disturbance effect accumulating over time; it would be interesting to see how the birds respond to the playbacks if the study was carried out longer
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First, there was no significant difference between the non-predator and predator playbacks, which may suggest that the birds did not know how to interpret the cues, which resulted in increased flight response and anti-predator behavior when they heard a noise they were not familiar with. I then find it surprising that the number of successful fledglings decreased in the second brood, as the sparrows continued to be distracted by the playback cues while never seeing a predator or growing accustomed to a sound that did not have a direct impact on their fitness. Subsequently, I was also wondering if the playbacks were used as the same frequency as natural predator calls; the playbacks were used repeatedly every few minutes, which may be more frequent than predator cues, which in turn might have a stronger effect on distracting the sparrows than the actual sound cues from the predators themselves. In addition, if the frequency of playbacks to predator cues are the same, then I presume there is a natural background masking noise that covers a proportion of the sounds natural predators make, as the sparrows appear to be more skittish around the playback sounds, thus emphasizing my previous point about the frequency of sound cues. I think investigating more studies such as this one will be beneficial in our literature search for how noise affects bird populations, as there may be more indirect effects interacting with measured direct effects than we originally
First, there was no significant difference between the non-predator and predator playbacks, which may suggest that the birds did not know how to interpret the cues, which resulted in increased flight response and anti-predator behavior when they heard a noise they were not familiar with. I then find it surprising that the number of successful fledglings decreased in the second brood, as the sparrows continued to be distracted by the playback cues while never seeing a predator or growing accustomed to a sound that did not have a direct impact on their fitness. Subsequently, I was also wondering if the playbacks were used as the same frequency as natural predator calls; the playbacks were used repeatedly every few minutes, which may be more frequent than predator cues, which in turn might have a stronger effect on distracting the sparrows than the actual sound cues from the predators themselves. In addition, if the frequency of playbacks to predator cues are the same, then I presume there is a natural background masking noise that covers a proportion of the sounds natural predators make, as the sparrows appear to be more skittish around the playback sounds, thus emphasizing my previous point about the frequency of sound cues. I think investigating more studies such as this one will be beneficial in our literature search for how noise affects bird populations, as there may be more indirect effects interacting with measured direct effects than we originally