Multiple log paths in bunyan

I'm using Bunyan with Restify to create an access.log which will store information about requests such as the endpoint, status-code etc... However, I'd like to separate the errors from this file and store them in a separate log-file.

I've tried creating the second error logger by adding an additional stream to the Bunyan logger instance, however errors aren't being written to error log-file. Any ideas why that is?

var log = new Logger({
  name: 'logga',
  streams: [
    {
      stream: process.stdout,
      level: 'debug'
    },
    {
      path: './logs/access.log',
      level: 'trace'
    },
    {
      path: './logs/error.log',
      level: 'error'
    }
  ],
  serializers: Logger.stdSerializers
});

server.on('uncaughtException', function (request, response, route, error) {
  log.error(error);
});