Experimental evidence that adult UV/yellow colouration functions as a signal in blue tit families — but only for parents

Abstract

In bi-parental species, reproduction is not only a crucial life-history stage where individuals must take fitness-related decisions, but these decisions also need to be adjusted to the behavioural strategies of other individuals. Hence, communication is required, which could be facilitated by informative signals. Yet, these signalling traits might have (co-)evolved in multiple contexts, as various family members usually meet and interact during reproduction. In this study, we experimentally explored for the first time whether a colourful plumage trait in adults acts as a signal that regulates multiple intra-family interactions in a bird species, the blue tit (Cyanistes caeruleus). We expected that an experimental reduction of adults’ UV/yellow reflectance (i.e. a reduction of apparent individual quality) should affect the behavioural strategies of all family members. We found evidence for this at least in adults, since the partners of UV-blocked individuals (either males or females) increased their parental investment — perhaps to compensate for the apparent lower condition of their mates. As the UV-blocked adult did not change its provisioning behaviour, the partner presumably responded to the manipulated signal and not to a behavioural change. However, the offspring did not co-adjust their begging intensity to the experimental treatment. It is thus possible that they responded to overall parental care rather than the signal. These results suggest that UV/yellow colouration of adult blue tits may act as quality signal revealing the rearing capacity to mates. Significance statement How parents respond to signals of genetic or phenotypic quality of their mates has received significant attention. However, previous studies have primarily focused on the receiver’s response and have not always controlled for the signaller’s behaviour and its investment in reproduction. Our results provide the first experimental evidence that ultraviolet (UV)/yellow colouration acts as a signal of parental quality in the blue tit. Parents responded by increasing their effort when paired with UV-blocked (low-quality) mates, while controlling for the mate’s behaviour. We argue that the reduced expression of the signal triggered a compensatory response in the mate. Interestingly, both males and females responded similarly to changes in mate’s UV/yellow reflectance, suggesting similar rules over investment in response to this trait. However, nestlings, a potential (and often neglected) set of observers of parental signals, did not change their behaviour when raised by an UV-blocked (= low-quality) parent.

Offspring plumage coloration as a condition‐dependent signal in the blue tit

“…However, nestlings of lutein supplemented mothers did not differ in coloration from control nestlings (one‐way ANOVA test; total brightness: F 1,670 = 2.13; p = .15; UV chroma: F 1,669 = 0.29; p = .59; carotenoid chroma: F 1,670 = 0.02; p = .89). In the 2018 season, we reduced the yellow UV chroma of one blue tit parent (indistinctly males and females) at the nest on the second week of nestling age (García‐Campa et al, 2022a ). Nonetheless, parental UV chroma did not have an effect on offspring color parameters (one‐way ANOVA test; total brightness: F 1,521 = 0.61; p = .44; UV chroma: F 1,521 = 1.20; p = .28; carotenoid chroma: F 1,521 = 0.78; p = .38).…”

“…Similarly, yellow breast feathers reliably reflect aspects of individual quality such as parasite burden (del Cerro et al, 2010 ), parental capacity (García‐Navas et al, 2012 ), and laying performance (Midamegbe et al, 2013 ). Furthermore, the UV chroma of adult breast plumage functions as a signal in parental interactions during offspring care (García‐Campa et al, 2022 ). Blue tit nestlings do not exhibit the UV/blue crown coloration, but there is some evidence that two color parameters of the yellow breast plumage, carotenoid chroma (Johnsen et al, 2003 ) and UV chroma (Jacot & Kempenaers, 2007 ; Morales & Velando, 2018 ), co‐vary with nestling body mass.…”

Offspring plumage colouration as a condition-dependent signal in the blue tit

“…Similarly, yellow breast feathers reliably reflect aspects of individual quality like parasite burden (del Cerro et al 2010), parental capacity (García-Navas et al 2012) and laying performance (Midamegbe et al 2013). Furthermore, the UV chroma of adult breast plumage functions as a signal in parental interactions during offspring care (García-Campa et al 2022). Here, partners of UV-reduced individuals (either males or females) increased their parental investment during offspring provisioning, perhaps to compensate for the apparent lower condition of their mates (García-Campa et al 2022).…”

“…Furthermore, the UV chroma of adult breast plumage functions as a signal in parental interactions during offspring care (García-Campa et al 2022). Here, partners of UV-reduced individuals (either males or females) increased their parental investment during offspring provisioning, perhaps to compensate for the apparent lower condition of their mates (García-Campa et al 2022). Blue tit nestlings do not exhibit the UV/blue crown colouration, but there is some evidence that two colour parameters of the yellow breast plumage, carotenoid chroma (Johnsen et al 2003) and UV chroma (Jacot & Kempenaers 2006;Morales & Velando 2018), co-vary with nestling body mass.…”

When parents play favorites: brood demand shapes parental preference for offspring UV color

“…In this species, the prominent yellow breast plumage is a carotenoid-based trait, which reflects light both in the human visible (yellow to red wavelengths; 550–700 nm) and in the ultraviolet region (300–400 nm) of the reflectance spectrum ( Johnsen et al 2003 ; Jacot and Kempenaers 2007 ). In adults, there is significant evidence that both the carotenoid-based coloration ( del Cerro et al 2010 ; García-Navas et al 2012 ; Midamegbe et al 2013 ) and the UV component of breast feathers ( García-Campa et al 2022 ) function as signals of quality. In nestlings, both the carotenoid-based and the UV component co-vary with body mass ( Johnsen et al 2003 ; Jacot and Kempenaers 2007 ; Morales and Velando 2018 ; see also Galván et al 2008 , in the closely related great tit, Parus major ), and nestling UV chroma is reduced in experimentally enlarged broods, in which competition for food might be enhanced ( Jacot and Kempenaers 2007 ).…”