Night's Black Bird is the first of seven works by Harrison Birtwistle coming up at the Proms in the composer's 80th birthday year, and it's a dark-hued, opaque gem. Inspired by a lute song by the arch-melancholic English Renaissance composer John Dowland, and written in 2004, it is a pungent depiction of night in which the comforting, enveloping aspects of darkness are somehow evoked in the same sinking, sliding music as its potential terror.

Much of it involves the kind of low, textured sounds whose nuances should by rights get flattened in this huge space. But Birtwistle's layered writing sounded silky and vital here as played by the BBC Philharmonic under Juanjo Mena, and the woodwind pealed out their bird calls spikily, as though they were the only elements of this piece not half hidden.

Ravel's Piano Concerto for the Left Hand was written for Paul Wittgenstein, who had lost a limb in the first world war, but it has always fascinated two-handed pianists too, as a kind of musically rewarding exercise in self-denial. Here, Alexandre Tharaud used his left hand for everything, even to turn the pages. His crisp attack, filigree delicacy and expansive flourishes made the orchestra seem a little stodgy by comparison. His languid, lyrical encore was Scriabin's Prelude for the Left Hand; anyone wanting to hear Tharaud's right hand will just have to come back another time.

From the start of Mahler's Fifth Symphony, Mena established two separate worlds: edgy brass v smooth, steady strings and woodwind. The problem was that the later moments of abandon didn't sound quite big enough in this acoustic to counterbalance the carefulness. I'd like to hear this interpretation again, but in a different hall, where the strings could make a visceral impact throughout and not only in the strings-only slow movement – which, in Mena's unindulgent reading, sounded at times almost brisk, but still gorgeous.

• The Proms continue until 13 September. Details: bbc.co.uk/proms.