Come on In

The weather has changed but last weekend was glorious. We paid a visit to Whipsnade Zoo and because it was a hot day we walked 'that bit further' to visit the penguins who are usually innactive on cool days, certain that they'd be doing water aerobics.
Instead they were all huddled at one end of their enclosure.

Others were lined up at the edge of the pool, as if ready for a race, but they had sent one in to test the water first. He/she seemed to be encouraging them in but to no avail. How hot does it have to get?