For experimental inference questions, distinguish directly observed effects from claims about untested mechanisms, life stages, or conditions. Select the choice that incorporates the principal findings and respects the study’s stated limitation without extrapolating beyond the evidence.
Hints
- Hint 1
Separate the observed effects
Determine what changed when illumination increased and what changed when traffic noise was played.
- Hint 2
Track the gap between the groups
Consider what it means that both groups shifted by about the same amount while the 18-minute difference remained.
- Hint 3
Distinguish evidence from extrapolation
Check whether each choice draws only conclusions supported by the tested conditions or makes a broader claim about mechanisms or prenatal effects.
Step-by-step
- Step 1
Identify the effects of the experimental conditions
Increased nighttime illumination caused both groups to become active earlier, whereas traffic noise produced no detectable change. Thus, the passage supports an immediate behavioral response to light but not to noise.
- Step 2
Interpret the persistent group difference
Urban-origin birds began activity earlier even when both groups were raised and tested under the same conditions. Because increased illumination shifted both groups by about the same amount and preserved the gap, light alone cannot explain the origin-associated difference.
- Step 3
Respect the experiment's limitation
The eggs were collected only after they had been laid, so the persistent origin-associated difference could reflect either genetic inheritance or maternal influences on the eggs. Therefore, the best completion is activity onset is shaped by both an immediate response to nighttime illumination and an origin-associated influence whose genetic or maternal basis remains unresolved.