The decision, made on 11 August, reaffirms the existing interpretation that it is illegal to inadvertently kill migratory birds.

Reuters reports that the 31-page ruling began by invoking the famed novel "To Kill a Mockingbird". US District Judge Valerie Caproni of Manhattan upheld a longstanding interpretation of the century-old Migratory Bird Treaty Act that energy companies and other businesses have opposed as too broad.

It marked the latest in a series of court rulings against numerous moves by President Donald Trump's administration to weaken environmental safeguards viewed as burdensome to industry.

Caproni's summary judgment held that a December 2017 Interior Department legal opinion by a Trump appointee reinterpreting the 1918 migratory bird statute violated the federal Administrative Procedure Act.

"It is not only a sin to kill a mockingbird, it is also a crime," the judge wrote.

"That has been the letter of the law for the past century. But if the Department of the Interior has its way, many mockingbirds and other migratory birds that delight people and support ecosystems throughout the country will be killed without legal consequence."

At stake in the case brought by several conservation groups and eight states was a policy, in effect since the early 1970s, defining an illegal "taking" under the migratory bird act as any action that caused the death of a protected species, whether deliberate or accidental.

The policy was also codified in a memorandum issued by the Interior Department at the very end of the Obama administration.

But a newly appointed Interior Department lawyer under Trump, Daniel Jorjani, suspended the Obama-era opinion.

Jorjani's own memo stated that the "taking" prohibition had been misconstrued to prosecute those who kill birds "incidentally" as part of doing business, but were really designed to prevent poaching and hunting without a license.

Jorjani held that the law applies only to "direct and affirmative purposeful actions" that destroy migratory birds, their eggs or their nests.

But Judge Caproni wrote that the Jorjani opinion "is simply an unpersuasive interpretation of the (1918 law's) unambiguous prohibition on killing protected birds."

Her ruling restores the longstanding incidental taking policy under the statute, enacted by Congress to implement a 1916 treaty between the United States and Britain.

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