Shell thickness and pore density in relation to shell colouration, female characteristics, and environmental factors in the Collared Flycatcher Ficedula albicollis

Abstract

Avian eggshell structure may have important consequences for embryonic growth and development, but relatively little is known about the factors responsible for variation in eggshell characteristics of wild birds. In this paper, we explored potential causes of variation in eggshell colour and structure (shell thickness and porosity) in the Collared Flycatcher (Ficedula albicollis). We analysed if eggshell colour is affected by shell structure or pigment level, and whether female traits, laying date, local breeding density, and clutch size affect shell thickness and pore density. We found that eggshell blue-green and UV colours were unrelated to shell thickness, pore density and egg size. Eggs with higher concentration of biliverdin showed lower UV reflection and higher reflection in the blue-green part of the spectrum. We found that females in better nutritional condition, indicated by their higher mass controlled for tarsus length, laid eggs with thicker shells. It is possible that females in better condition have more time available for searching calcium-rich food, and thus could produce eggs with stronger shells. However, female physical characteristics had no significant relationships with shell porosity. In contrast to our expectation, shell thickness and pore density were unrelated to local breeding density and laying date, though very late and repeat clutches were not sampled in our study. However, we found that eggs in larger clutches had lower pore density than eggs in smaller clutches, which may be expected if the rate of water loss and nest humidity are to remain constant in clutches of different egg numbers.Zusammenfassung Die Struktur der Eischale von Vögeln kann wichtige Folgen für das Wachstum und die Entwicklung der Embryonen haben, doch über die Faktoren, die für Variation in den Eigenschaften der Eischale bei freilebenden Vögeln verantwortlich sind, ist relativ wenig bekannt. In diesem Artikel haben wir mögliche Gründe für die Variation in Eischalenfarbe und -struktur (Schalendicke und Porosität) beim Halsbandschnäpper (Ficedula albicollis) untersucht. Wir haben analysiert, ob die Eischalenfarbe von der Schalenstruktur oder dem Pigmentgehalt beeinflusst wird und ob Weibchenmerkmale, Legedatum, lokale Brutpaardichte und Gelegegröße die Schalendicke und Porendichte beeinflussen. Wir fanden, dass blaugrüne und ultraviolette Farben der Eischale nicht mit der Schalendicke, Porendichte und Eigröße zusammenhingen. Eier mit einer höheren Biliverdinkonzentration zeigten eine geringere UV-Reflexion und stärkere Reflexion im blaugrünen Bereich des Spektrums. Wir fanden, dass Weibchen in besserem Ernährungszustand, angezeigt durch ihre höhere Körpermasse korrigiert für Tarsuslänge, Eier

Effects of environmental conditions on the egg mass, yolk antioxidant level, eggshell thickness and eggshell spotting patterns of Great Tits (Parus major)

“…This foraging flexibility of Great Tits could possibly be the reason why we found that environmental conditions had no significant effect on eggshell thickness. Our results are in concordance with previous findings, as eggshell thickness also did not vary with laying date and ambient temperature in other bird species (Eeva and Lehikoinen 1995;Massaro and Davis 2004;Hargitai et al 2011;Stein and Badyaev 2011).…”

Eggshell biliverdin concentration does not sufficiently predict eggshell coloration

“…This finding is in accordance with recent investigations of the ability of other non‐pigment‐based factors to drive variation in eggshell coloration, including eggshell smoothness (Igic et al ) and cuticle properties (Fecheyr‐Lippens et al ). More specifically, the importance of eggshell thickness in explaining variation in coloration has been documented in pied flycatchers Ficedula hypoleuca (Morales et al ), although no effect was detected in collared flycatchers Ficedula albicollis (Hargitai et al ) or spotless starlings Sturnus unicolor (López‐Rull et al ). However, these studies, in addition to the work presented here, relied upon light that is reflected off the eggshell to quantify coloration.…”

A Review of the Relationship between Eggshell Colour and Water Vapour Conductance

“…The degree of pigmentation did not significantly affect shell thickness and water vapour conductance values for samples of shell pieces from either the speckled or plain areas did not differ significantly. Similarly, in the collared flycatcher (Ficedula albicollis) neither shell thickness nor pore density are affected by variability in shell colouration as measured in the blue-green or UV chroma (Hargitai et al, 2011).…”