What insects are available to chicks?

Key findings

• Human-imprinted chicks eat the same insects as wild chicks.
• Insect selection by chicks appears to be instinctive.
• Human-imprinted chicks can further our knowledge on the habitat needs of gamebird broods.

Insects play a crucial role in the diet of gamebird chicks, and biologists often use insect abundance to measure how important different habitats are for foraging broods. The greater the abundance of insects the better, but not all insects are available, with many being beyond the reach of chicks. For this reason, insect abundance, as measured by standard insect sampling techniques such as sweep-netting and vacuum samplers, does not accurately reflect the foraging value for chicks.

To provide a more biologically relevant assessment of brood habitats, researchers in the United States have begun using hand-reared northern bobwhite quail chicks foraging in the wild. The chicks are first imprinted onto the researchers, so that the chick forms a bond to a parent figure, in this case a human, shortly after hatching. When the chicks are eight to 12 days old, they are then taken into the field and allowed to forage in small groups with the handler following closely. After half an hour, the chicks are gathered up and penned overnight where their faeces are collected and examined for insects.

Although human-imprinted chicks may offer an appropriate method for assessing the foraging value of brood habitats, the validity of this new technique remained untested. Because imprinted chicks have little foraging experience, a key assumption is that insect selection by gamebird chicks is instinctive. To test this, we collaborated with Tall Timbers Research Station in Florida to compare the insect selection by wild and human-imprinted northern bobwhite chicks.

Table 1: Prevalence of seven invertebrate groups in diet of wild and human-imprinted northern bobwhite quail chicks, 2003-2004

During 2003 and 2004, we collected faecal samples from the night roosts of 18 radio-collared wild broods. In the afternoon before collecting these samples, imprinted chicks were allowed to forage at locations where the radio-collared wild broods had been found one to two hours previously. We analysed the faecal samples from both chick types to determine the insect composition of their diets. We also collected insect samples using a vacuum sampler to assess overall insect abundance. The faecal samples of the imprinted chicks contained the same insect groups as those of wild chicks (see Table 1). Beetles, plant bugs and ants accounted for over 80% of both diets, but the proportions varied between the two types of chick. A higher proportion of ants were found in the diet of imprinted chicks.

The results of this study suggest that insect selection by human-imprinted bobwhite quail chicks is similar to wild chicks. Such chicks could therefore provide a more ‘chick-relevant’ technique for measuring the foraging value of habitats than standard methods. In 2007, we began a PhD project that used imprinted pheasant chicks to assess the insect availability in brood-rearing habitats in Austria.