OutOfMemoryError with RabbitMQ River

I've been trying out the RabbitMQ river, but have quickly hit problems.

Here's what I am doing::

  1. I sent 2,500 messages to RabbitMQ, each containing 100 documents in
    bulk api format
  2. I create a RabbitMQ river using curl, with bulk size 1 (I tried 100
    first BTW, and got the same result)
  3. About 40,000 documents get indexed OK by elasticsearch

elasticsearch them crashes with:

Exception in thread "elasticsearch[Nameless One][rabbitmq_river][T#1]"

java.lang.OutOfMemoryError: unable to create new native thread
at java.lang.Thread.start0(Native Method)
at java.lang.Thread.start(Thread.java:691)

I'm running elasticsearch 0.19.10, with version 1.4.0 of the RabbitMQ
river. The river I created is accessing a remote instance of RabbitMQ.

I've read in this group that others are using this river successfully, so
was not expecting this - am I doing something wrong?