Relationship between laying sequence and mercury concentration in tree swallow eggs.

Area of Science:

• Environmental toxicology
• Avian biology
• Ecotoxicology

Background:

• Mercury is a toxic heavy metal that bioaccumulates in organisms.
• Female birds can transfer mercury to their eggs during laying.
• This transfer could lead to a decrease in mercury levels within a clutch over time.

Purpose of the Study:

• To investigate mercury levels in tree swallow (Tachycineta bicolor) eggs.
• To determine if mercury concentration declines with the laying sequence in a clutch.
• To assess the reliability of sampling a single egg for estimating clutch mercury contamination.

Main Methods:

• Analyzing mercury concentrations in individual tree swallow eggs from a contaminated site.
• Comparing mercury levels across different positions within the laying sequence of clutches.

Main Results:

• No significant decline in mercury concentration was observed with the laying sequence in tree swallow clutches.
• This suggests that females may replenish mercury levels daily during egg formation.
• A single egg sample accurately reflects the overall mercury contamination of the clutch.

Conclusions:

• Daily mercury replenishment in female tree swallows prevents a decline in egg mercury levels across a clutch.
• Sampling a single egg is a valid method for assessing mercury contamination in tree swallow clutches.
• Understanding mercury transfer dynamics is crucial for avian ecotoxicology and conservation efforts.