Birds excrete ammonia as the principal nitrogenous end product in the urine.

Answer

### Step-by-Step Solution:

1. **Understanding Nitrogenous Waste**:
- Nitrogenous wastes are products of protein metabolism and can be excreted in various forms by different organisms. The main types are ammonia, urea, and uric acid.

2. **Types of Nitrogenous Waste Excretion**:
- **Ammonotelic**: Organisms that excrete ammonia as their primary nitrogenous waste. This is typical for aquatic animals (e.g., fish) because ammonia is highly soluble in water and can be easily diluted.
- **Ureotelic**: Organisms that excrete urea. This is common in mammals, including humans, as urea is less toxic than ammonia and requires less water for excretion.
- **Uricotelic**: Organisms that excrete uric acid. Birds, reptiles, and some insects fall into this category. Uric acid is less toxic and conserves water, making it advantageous for terrestrial animals.

3. **Birds and Their Excretion**:
- Birds are classified as uricotelic organisms. They primarily excrete uric acid, not ammonia. This adaptation allows them to conserve water, which is crucial for survival in their often arid environments.

4. **Conclusion**:
- The statement that "birds excrete ammonia as the principal nitrogenous end product in the urine" is **false**. Birds excrete uric acid, making them uricotelic, while ammonia is primarily excreted by ammonotelic organisms, typically aquatic animals.

### Final Answer:
The statement is **false**. Birds excrete uric acid, not ammonia, as their principal nitrogenous end product.

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