Calcium metabolism in birds gets disturbed due to the effect of:

Options

A. mercury
B. cadmium
C. DDT
D. lead

Answer

### Step-by-Step Solution

1. **Understanding Calcium Metabolism in Birds**:
- Calcium is crucial for birds, particularly for the formation of eggshells, which are primarily composed of calcium carbonate. This composition is essential for providing structural strength and support to the eggs.

2. **Identifying the Importance of Calcium**:
- The eggshell's integrity is vital as it prevents premature breaking. If calcium metabolism is disrupted, it can lead to weakened eggshells, which can result in higher rates of egg breakage and consequently, a decline in bird populations.

3. **Recognizing the Factors Affecting Calcium Metabolism**:
- Various metals and compounds can affect calcium metabolism. In this context, we are considering mercury, cadmium, lead, and DDT.

4. **Analyzing the Role of DDT**:
- DDT (Dichloro-Diphenyl-Trichloroethane) is a pesticide known to disrupt calcium metabolism in birds. It interferes with the hormonal regulation of calcium, particularly affecting hormones secreted by the parathyroid gland and thyroid gland.

5. **Consequences of Disrupted Calcium Metabolism**:
- The disruption caused by DDT leads to thinning of the eggshells, making them more susceptible to breaking. This results in the death of embryos inside the eggs, as they are not mature enough to survive outside the shell.

6. **Conclusion**:
- Among the options provided, DDT is the compound that significantly disrupts calcium metabolism in birds, leading to detrimental effects on their reproductive success.

### Final Answer
**DDT is the compound that disturbs calcium metabolism in birds.**

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