Unlike mammals, the lead shot does not pass through the alimentary 
canal, but stays in the birds' gizzards, along with gravel that is 
co-picked up. When a bird eats, the food (brine shrimps, stones and 
shot) gets only as far as the gizzard, where a muscular movement causes 
it to be ground up by the ingested stones and it passes to the stomach 
only when it is thoughly puréed. The shot and stones remain in the 
gizzard. The friction of the stones on the shots also grinds up the lead 
into progressively more microscopic "filings" with a progressively 
greater surface area. These obviously oxidise and the oxides are also 
ground off and eventually enter the stomach, where they will react with 
the acidic juices and be absorbed.

Brian

Dave Delman (MA/NY DDave wrote:
> Hi Brian, ENet Listservers,
> 
> By the way this comes from Lead Free, Jan05 under another topic.
> 
> So Brian do you have any idea of how the lead enters across the barrier. It
> shouldn't come in as pure lead, right!!. Taking in sea water and such there
> might be a chemical reaction and the lead is coming in as part of another
> chemical compound.
> 
> If you don't know you can at least postulate.
> 
> Yours in Engineering, Dave
> Y i Engr, MA/NY DDave
> 
> <Yes, there has been one problem. It has been found that a few flamingoes
> which winter in a large salt lake close to where I live died from
> ingesting lead pellets. Unlike sheep, these birds eat brine shrimp on
> the lake bottom and naturally ingest the shrimp and pebbles together.
> The pebbles remain in the birds' gizzards and serve to grind up the
> food, much as we do with our teeth. Lead shot, which the birds may pick
> up, also stay in the gizzard and are themselves ground up by pebbles and
> relatively large amounts of finely divided lead enter the stomach, where
> it interferes with the enzymes and may be partially metabolised.
> Investigation showed that a clay-pigeon range overshot the lake. This
> was closed down and the authorities dredged the affected area to remove
> over 100 tonnes of lead! Interestingly, there was no reduction of the
> brine shrimp population in that area, so it may be assumed that there
> was no significant entry of lead in the birds' food chain before they
> ingested the pellets as metallic lead. This winter, there have been no
> reported deaths of the highly protected flamingoes, that I'm aware of.>
>