Migration in birds is guided in part by -

Options

A. Celestial navigation
B. Temperature changes
C. Territorial aggression
D. All of the above

Answer

To answer the question regarding what guides migration in birds, we can break down the options provided and analyze them step by step.

### Step-by-Step Solution:

1. **Understanding Bird Migration**:
- Bird migration is a seasonal movement of birds from one region to another, typically in search of food, breeding grounds, or favorable climates.

2. **Evaluating the Options**:
- **Option 1: Salicyl Navigation**: This term seems to be a misnomer or incorrect. There is no widely recognized concept of "salicyl navigation" in ornithology.
- **Option 2: Temperature Changes**: Temperature changes can influence migration patterns as birds often migrate to warmer areas during colder months.
- **Option 3: Territorial Aggression**: While territorial behavior can play a role in breeding seasons, it is not a primary factor in guiding migration.
- **Option 4: All of the above**: This option suggests that all previous options are correct, but since Option 1 is incorrect, this option cannot be correct.

3. **Identifying Key Factors in Bird Migration**:
- Birds use various navigational aids during migration, including:
- **Earth's Magnetic Field**: Many birds can sense the Earth's magnetic field and use it for orientation.
- **Sun**: Birds can navigate using the position of the sun during the day.
- **Stars**: Nocturnal migrants often use stars for navigation at night.
- **Landmarks**: Birds may also use physical landmarks for guidance.

4. **Conclusion**:
- Based on the evaluation, the most relevant factors guiding bird migration are temperature changes, the Earth's magnetic field, the sun, and the stars. However, the options provided in the question do not include the most accurate navigational aids.

### Final Answer:
Migration in birds is guided in part by **temperature changes** and other factors like the Earth's magnetic field, the sun, and stars, but the options provided do not accurately represent the primary guiding factors.