Ornis Fennica 95: 160170.2018 Capercaillie (Tetrao urogallus) eggshell pigmentation, maculation and thickness Joanna Rosenberger*, Ewa £ukaszewicz, Artur Kowalczyk & Zenon Rzoñca J. Rosenberger, E. £ukaszewicz, A. Kowalczyk, Wroclaw University of Environmental and Life Sciences, Institute of Animal Breeding, Division of Poultry Breeding, Che³moñ- skiego 38c, 51-630 Wroc³aw, Poland. * Corresponding authors e-mail: joanna. [email protected] Z. Rzoñca, Forestry Wis³a, Czarne 6, 43-460 Wis³a, Poland Received 27 March 2028, accepted 12 September 2018 Eggshells properties (mainly thickness, pigmentation and shape) vary within avian taxa across species, and intraspecifically with age, environmental conditions or individual fea- tures of the animals. The properties and appearance of eggshells are important for suc- cessful breeding both for birds kept in captivity and in breeding centres and those living in their natural environment. The presented study focuses on the association between the pigmentation, maculation and eggshell thickness of Western Capercaillie (Tetrao uro- gallus) kept in captivity. The eggs were collected during the entire egg-laying season in order to determine the factors which influence eggshell pigmentation and thickness across the laying period. We found that at the equator surface the lightest eggs had a ten- dency to be thinner than the darkest ones. In addition, eggshells with a smooth pattern were thinner at the equator, especially when compared to the mottled ones. There was no statistically significant association between the eggshell overall lightness (eggshell pig- mentation except the concentrated pigment spots), maculation and eggshell thickness at the blunt and sharp ends of the eggshell. Eggshells were on average 5.5% thicker at spots than in other areas. The obtained results suggest that the spot pigment forms an additional layer on the Capercaillie eggshell and does not compensate for the loss of thickness, as ob- served in some bird species (Passeriformes, Falconiformes). A negative association be- tween the eggshell thickness and the laying date (comparing eggs laid in April and June) was also observed, despite the availability of a variety of food and ad libitum calcium supplementation during the entire reproductive season. The eggshell coloration was not related to the period of egg-laying. We have shown the effect of pigmentation on one of the most important parameters of eggshell quality, shell thickness. In the case of Caper- caillie, the places of eggshell thinning are not related to concentrated pigment spots. This suggests that the pigment deposition and its role may be different from other bird orders (Charadriiformes, Falconiformes, Passeriformes). Rosenberger et al.: Capercaillie eggshell pigmentation, maculation and thickness 161 1.Introduction where lateralization is strongly developed). This may explain secondary development of white egg- The egg coloration of early avian species was shells. Pigmentation must allow light to penetrate white, similarly to reptile eggs (Kilner 2006). the eggshell in order for the embryo to establish the Modern bird eggs vary in shape, background pig- circadian rhythm(Zeman et al. 1999). mentation (base-colour) and maculation (spotti- Eggshell pigmentation and maculation are af- ness). Across all avian species, open-nesting spe- fected by many factors, with variation between cies such as Capercaillie (Tetrao urogallus)tend and within species, and research implies that they to lay more pigmented eggs than hole-nesting spe- impact the breeding success in birds. Embryonic cies (Lack 1968). These eggshell pigments belong light stimulation plays a significant role in the reg- to two blood-derived groups: protoporphyrin that ulation of chromatin repair by photo-reactivation provides brown, red, yellow and black colours, (Thoma 1999). This is important during numerous and biliverdin, responsible for the blue-green col- cell divisions in the developing embryo, where an oration (Kilner 2006). Capercaillie eggs are of dif- erroneous division may have critical conse- ferent shades of brown which indicates proto- quences on the organism. In addition, pigments porphyrin pigmentation (Kennedy & Vevers may prevent pathogen infections. Ishikawa et al. 1976). (2010) showed light-dependent antimicrobial pig- All eggshell pigments are deposited in the shell mental activity against Staphylococcus aureus and gland during the latest stages of shell formation Bacillus cereus. (Poole 1965, Roberts 2004), and their functions Some authors (Higham 2006, Kilner 2006, are complex. While egg pigmentation seems to be Gosler et al. 2011) stated that pigments also play a genetically predetermined or fixed, the pigment structural function affecting eggshell thickness intensity and pigment spread may change in birds and strength. Those factors are linked with dietary with age (Odabaºi et al. 2007) and the egg laying calciumavailability (Graveland & Drent 1997, order (Gosler et al. 2005). Eggshell pigmentation Dhondt & Hochachka 2001, Tilgar et al. 2005), may even be affected by weather conditions pesticide levels (Ratcliffe 1970) or environmental (Avilés et al. 2007). There are many hypotheses acidification (Nybø et al. 1997). However, the re- regarding the function of egg pigmentation. One lationship of those factors with pigmentation and of the first and most common hypotheses suggests maculation has not been examined in many bird that it prevents egg depredation (Blanco & Ber- species, including Western Capercaillie. For ex- tellotti 2002, Sanchez et al. 2004), especially in ample, several studies (Gosler et al. 2005, Higham ground nesters (Weidinger 2001) and brood para- & Gosler 2006, Jagannath et al. 2008, Sanz & sites (Davies & Brooke 1989a,b, Avilés et al. García-Navas 2009) have reported an association 2007). between the maculation pattern and the eggshell It has also been observed that less pigmented thickness. They suggested that pigments play a eggs were characterized by higher embryo mortal- role in compensating for the eggshell thinning ity related to an excessive water-loss (Higham& caused by structural variations in the shell and cal- Gosler 2006). According to more recent theories cium deficiency. Similarly, Solomon (1987, 1997) focusing on eggshell pigmentation on thermal suggested that protoporphyrin may strengthen a properties during embryogenesis (Moreno & crystalline matrix by acting as a shock absorber. Osorno 2003), embryos developing in the lighter Not only maculation, but also lightness influence eggs are more resistant to high temperature as they eggshell thickness (Or³owski et al. 2017). The pale are exposed to less heat gain fromsolar radiation eggs collected from Common Quail (Coturnix (Westmoreland et al. 2007, Magige et al. 2008, coturnix) had thinner eggshells compared to the Maurer et al. 2011b). Rogers & Krebs (1996) dark ones. However, the eggshell lightness itself stated that chicks that hatched fromeggs which has been investigated to a much lesser extent than were exposed to light during incubation, showed maculation. structural asymmetries in the brain, and conse- Many studies have shown direct and indirect quently performed better in a number of behav- pigmentation impacts on eggshell properties ioural tasks (in cavity nesters, especially parrots, (Darnell-Middleton et al. 1998, Gosler et al. 2005, 162 ORNIS FENNICA Vol. 95, 2018 Bain et al. 2006, Higham& Gosler 2006, Jagan - 2.2. Eggshell evaluation nath et al. 2008, Sanz & García-Navas 2009), but also on other egg parameters, like egg shape, that After incubation, 150 unhatched eggs were col- cannot be overlooked. Even within one species it is lected for further examination. Because we were easy to observe the diversity related to egg length not sure which eggs were laid by which birds and width. Thus, in our analyses we also studied (some eggs were laid outside the nest or in the associations between egg shape, eggshell light- other one) we were not able to exclude pseudo- ness, strength and laying period. replication. The strength (crush test) of unhatched The main aim of this study was to examine eggs with undamaged shells was measured using whether the overall pigmentation (eggshell pig- the EGG Force Reader (ORKA Food Technology mentation except the concentrated pigment spots) LTD). The eggs were placed in the egg cradle ver- and maculation of the Western Capercaillie egg- tically, with the blunt end directed upwards. Then, shell compensates the loss of eggshell thickness, a force gauge was applied to the upper surface with as in the other bird orders (Passeriformes, Falconi- a gradual increase in the applied pressure. The mo- formes) (Gosler et al. 2005, Higham& Gosler ment of eggshell cracking was recorded to the 2006, Jagannath et al. 2008, Sanz & García-Navas nearest 0.001 kg. An electronic calliper was used 2009). The majority of authors have not clearly to measure the maximum egg length and width, to distinguished these two traits, probably because the nearest 0.01 mm. After the evaluation of the they are related to each other. eggshell, each egg was opened to define its content We decided to separate themto see which of (unfertilized egg or containing a dead embryo). them can have a more important impact on egg- Due to the fact that there are no available tables shells. Based on our previous observations (Ro- describing the embryo development of the Caper- senberger et al. 2016) we predicted that pigments caillie, we adopted tables created for the Helmeted may influence