Scientists have discovered evidence of Deepwater Horizon oil among land-based birds -- a reminder of the far-reaching effects of the 2010 disaster.

The new findings, detailed in the journal Environmental Research Letters, are also a reminder of the interconnectedness among habitats, ecosystems and food chains.

"At first, you may not imagine that a terrestrial bird would be impacted by an oil spill in the ocean, but in nature boundaries are often blurry," Andrea Bonisoli Alquati, a former Louisiana State University researcher now at California State Polytechnic University, Pomona, said in a news release. "As a result, contaminants that are supposed to stay in aquatic environments can make it 'onto' land."

The researchers use carbon dating methods to analyze the feathers and stomach contents of sea sparrows, Ammodramus maritimus, living marshes affected by the oil spill. They also analyzed sea sparrows from unaffected marshes.

"The two tissues provide information over different time-scales, with feathers integrating longer periods of exposure than stomach contents, which give a more recent snapshot of events," added Bonisoli Alquati.

Scientists found sea sparrows in marshes affected by the spill featured less radiocarbon content, evidence that remnants of the oil spill have been absorbed by the birds.

Similar analysis of the soil revealed the presence of biomarkers linked to the oil spilled in the wake of the Deepwater Horizon oil rig explosion. The same biomarkers were absent from control sites.