Effects of age, sex and social isolation on contrafreeloading in red junglefowl (Gallus gallus) and White Leghorn fowl

Contrafreeloading (CFL), i.e. choosing to work to obtain food over free food, has been studied in many different species. White Leghorn laying hens selected for high production have a lower extent of CFL compared to their wild ancestor, red junglefowl. We studied the effects of age, sex and social isolation, on the extent of CFL in red junglefowl and White Leghorn layers.For 48 h, 30 birds of each breed were allowed a choice, between freely available food and food mixed with wood shavings. Both females and males were tested individually as young birds (8–10 weeks old) and when they were sexually mature (27–29 weeks old). To test the possible effects of social isolation, the same birds were also tested in pairs at 30 weeks of age.Junglefowl showed a higher extent of CFL at the younger age compared to Leghorns (33.7% vs. 22.7%; P = 0.05) and both breeds showed higher extent of CFL at a young age than when sexually mature (P < 0.001). There were no significant differences between the two breeds when they were sexually mature and tested individually but, when tested in pairs, junglefowl showed higher extent of CFL than Leghorns (31.7% vs. 17.0%; P < 0.001). There were no differences in the extent of CFL between the sexes in either breed.The results indicate that age and social isolation influence the extent of CFL in fowl. Furthermore, the results support earlier findings that the extent of CFL is lower in Leghorns than junglefowl, indicating a possible side-effect of selection for increased production.