A finding question about competing causes tests whether you can tell which cause the evidence supports. Read the account being tested, and put its cause and effect in a few words. Then ask why the passage says those causes are hard to separate. Separate the possible causes by looking for findings that test one without changing the other. The strongest support helps rule out the other cause, since evidence that fits both causes can't tell them apart.
Hints
- Hint 1
Put Velez’s account in a few words: what might make the robins begin singing earlier, and why?
- Hint 2
Read why ordinary urban-rural comparisons make the account hard to test. What makes the two possible causes hard to separate?
- Hint 3
Return to the sentence about singing before commuting begins. Ask how that reason for singing connects to when the dawn song starts.
Step-by-step
Separate traffic from light
Step 1Identify the cause and effect
The robins’ earlier dawn song is what a supporting finding must explain. What cause does Velez’s team propose? They say traffic noise may drive much of this pattern, because singing before commuting avoids engine noise. The claim links traffic to an earlier start.
- Step 2
Predict a test that separates the causes
Why can't we settle the cause by comparing city and rural sites? Cities with dense road networks also tend to install more nighttime lighting, so brightness and traffic vary together. Let's hold brightness steady so a difference in singing can't be blamed on a difference in light. From shifting more singing into the period before commuting begins, we predict song start times that change with commuting times at similarly bright sites.
- Step 3
Check what the findings actually show
Do the findings explain earlier dawn song? The traffic was louder finding shows an earlier start, but the birds keep the same start time after commuting times shift. That works against the idea that birds start earlier to avoid traffic noise. Later singing after dimmer bulbs, with traffic unchanged, points to light as the cause. A greater share of songs before traffic leaves the start relative to sunrise unchanged, so more singing before traffic isn't the same as starting earlier.
- Step 4
Use both parts of the strongest finding
At comparable nighttime brightness, earlier traffic goes with earlier singing, so brightness can't explain that gap. What does the bright-park comparison add? Birds in bright parks without early traffic start like those in dark, quiet preserves, supporting the idea that light has little direct effect on song timing. Both parts support traffic rather than brightness. Choice A.