Sniff test for plover chicks

Who are my parents?

Imagine you’re a young chick in a bustling colony or a busy nesting site. The world is full of adult birds, but which one is your parent? Recognising family members is crucial in the animal kingdom, as it for example allows to care for relatives or to avoid inbreeding. It can be important even early in life. Indeed, young that are able to identify their parents correctly may receive more food and protection, while those that fail may be ignored—or worse, attacked. This is especially true for precocial species, whose young leave the nest soon after hatching and therefore risk losing contact with their parents and encountering foreign adults. If they solicit care from the wrong adult, they might face rejection or even aggression.

The scent of family

How can chicks recognise their parents? Birds have long been thought to rely essentially on visual and auditory cues for parent-offspring recognition, but recent research suggests that some species may also use smell. Studies have shown that adult birds can identify the scent of their nest, eggs, and even chicks, while young birds can recognise familiar nest odours. However, only two studies have tested whether young birds can recognise their parents by smell. Interestingly, both studies were conducted on altricial species (zebra finches and tree swallows), which stay in the nest for an extended period, and thus may not really benefit from discriminating between parents and foreign adults (Caspers et al. 2017; Griebel & Johnston 2020). This raises the question: do precocial chicks, which may have a greater need for parent recognition, also use olfactory cues to identify their parents?

Figure 1. A White-fronted Plover chick in Madagascar © Marc Gilles.

Finding a study species

To answer this question, we needed a study species with precocial chicks that are likely to encounter foreign conspecific adults. We decided to work on White-fronted Plovers (Figure 1), a precocial shorebird species, in southwest Madagascar, where they nest at relatively high densities. White-fronted plover chicks are likely to encounter foreign adults, especially when they lose contact with their parents, for example after a territorial fight between adults.

Figure 2. Behavioural trials were conducted on white-fronted plover chicks (left) using a Y-maze in the field (right) © Marc Gilles.

Sniff test

To test if chicks are able to recognise the smell of their parents, we used a Y-maze directly in the field (Figure 2). Chicks were first given a choice between the odour of an unfamiliar adult and a control (no odour), and then between the odour of a parent and that of an unfamiliar adult. If chicks could recognise parental odour, we predicted that they would prefer it. Alternatively, if there is no cost to soliciting care from non-parents, they should show attraction to any adult odour. To assess whether the chicks prefer an odour or the other, we measured the time they spent with each odour during the 15 minutes trial. As test odours, we used swabs of preen oil—an important source of body odour in birds—which were freshly collected from adult birds and then placed at the end of the Y-maze arms (Figure 3).

Figure 3. Left: Y-maze trial used to test olfactory preferences in plover chicks. At the start of a preference trial (i.e. when the door of the acclimation chamber was opened), the plover chick was allowed to explore the two test arms, from which came the odours, circulated by an air flow. To measure olfactory preferences, we recorded videos of the trials from above and measured the amount of time the chick spent with each test odour (i.e. in the preference zones) and which test odour it visited first. Right: time spent by plover chicks with (a) the odour of an unfamiliar adult versus no odour (conspecific odour discrimination trial, N = 29 trials) and with (b) the odour of an unfamiliar adult versus the odour of a parent (parent odour discrimination trial, N = 24 trials) © Marc Gilles.

No preference, no discrimination?

Contrary to our predictions, we found neither a preference for the odour of an unfamiliar adult over a control (no odour) nor a preference for the odour of a parent over that of an unfamiliar adult (Figure 3). We therefore found no evidence for olfactory parent recognition in this precocial species. It may be that plover chicks do not need to discriminate between parents and foreign adults, or that they rely on other (e.g. auditory) cues. It is also possible that chicks can discriminate parental and unfamiliar odours but that our experiment failed to detect it. More research is needed to understand how common and important olfaction is for parent recognition in birds. Precocial species are well suited to address this question, as (1) they probably need parent–offspring recognition, and (2) Y-maze trials can easily be conducted on mobile chicks (Featured Image).

References