Birds of northern cold areas migrate southwards as the days

Options

A. Begin to shorten
B. Begin to lengthen
C. Become neutral
D. None of the above.

Answer

**Step-by-Step Solution:**

1. **Understanding Migration:** Birds migrate to find suitable habitats and environments for survival. This is often influenced by seasonal changes in their environment.

2. **Identifying the Trigger for Migration:** In northern cold areas, birds typically migrate southwards during the winter months. The primary trigger for this migration is the change in daylight.

3. **Analyzing Daylight Changes:** As winter approaches, the days begin to shorten. This reduction in daylight signals to birds that it is time to migrate to warmer areas where food and nesting sites are more abundant.

4. **Conclusion on the Question:** Given the options provided:
- "Begin to shorten" is correct because it aligns with the phenomenon of birds migrating south as winter approaches.
- "Begin to lengthen" is incorrect because this occurs during spring and summer.
- "Become neutral" does not apply as it does not reflect the changes in day length.
- "None of the above" is also incorrect since one of the options is indeed correct.

5. **Final Answer:** The correct answer is that birds of northern cold areas migrate southwards as the days begin to shorten.

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