Partridge food experiment

Key findings

• Chicks that were fed beetles, snails or ants (known to be potential carriers of parasites) did not contract parasites. 
• Growth rates of chicks fed on beetles, snails or ants were higher than those fed just chick crumb
• Reduced chick survival is more likely to be caused by lack of food rather than parasite infection.

In this study, we experimentally altered the food availability of reared grey partridge chicks to test whether the consumption of invertebrates known to carry parasitic worms caused increased parasitic infection in partridges.

We kept 20 batches of 12 one-day-old grey partridge chicks in captivity on a sterile substrate. We fed all batches with a standard diet of chick crumb but, for the first three weeks, we augmented the diets of 15 batches with ants, beetles and snails, which are all known to be vectors of parasitic disease. Five batches received adult ants, five a variety of small snails and five carabid beetles, with the remaining five batches receiving the standard diet as a control. We allocated the diet randomly to each batch.

We also sealed the joints in the pens containing each batch and employed bio-security measures to prevent cross-contamination. In total, the experiment involved the collection and feeding of over 3,000 beetles, 3,000 snails and over 10,000 ants. We monitored the chicks and examined their faeces microscopically to confirm that the invertebrates had been eaten.

In most cases chicks consumed all invertebrates within seconds of being fed them. We measured food (chick crumb) consumption and body size (wing length, body weight and tarsal length) daily and weekly, respectively. After six weeks, we conducted post-mortems on all chicks that had not died previously to establish the number and species of internal parasitic worms.

After receiving an augmented diet for three weeks and allowed to grow until six weeks old, none of the chicks fed an experimental diet contracted parasites. Although there was no difference in the amount of non-invertebrate food consumed by the different groups, the growth rates of chicks eating ants and beetles were higher, on average, than those of chicks eating snails or an unsupplemented diet (see Figure 1).

	Beetles
	Ants
	Snails
	Chick crumb diet

Across the batches and throughout the supplementary feeding part of the experiment, a huge number of invertebrates were fed. It is therefore very likely that the chicks were potentially exposed to parasites. Moreover, the quantity of invertebrates fed to the chicks supplemented the diet to such an extent that they grew better.

The lack of parasitic infection shows that either the infection rate must be very low or that some other factor may be controlling the contraction of disease. Unlike wild grey partridges, the chicks reared under the experimental conditions had all the requirements for good growth, namely a permanent supply of warmth, light, water and a high-protein diet. It is possible that under these ideal conditions grey partridge chicks have a much better immunity to parasitic infection.

Our conclusion from the two studies looking at disease in wild grey partridges is that disease and the apparent reduction in chick survival is most likely to be the result of reduced food availability, rather than an increase in parasite infection.