D. Charles Deeming

An Egg-Adult Association, Gender, and Reproduction in Pterosaurs

A pterosaur fossil that includes a small, soft-shelled egg indicates a reproductive strategy like that of crocodilians. A sexually mature individual of Darwinopterus preserved together with an egg from the Jurassic of China provides direct evidence of gender in pterosaurs and insights into the reproductive biology of these extinct fliers. This new find and several other examples of Darwinopterus demonstrate that males of this pterosaur had a relatively small pelvis and a large cranial crest, whereas females had a relatively large pelvis and no crest. The ratio of egg mass to adult mass is relatively low, as in extant reptiles, and is comparable to values for squamates. A parchment-like eggshell points to burial and significant uptake of water after oviposition. This evidence for low parental investment contradicts the widespread assumption that reproduction in pterosaurs was like that of birds and shows that it was essentially like that of reptiles.

First‐egg date and air temperature affect nest construction in Blue Tits Cyanistes caeruleus, but not in Great Tits Parus major

Capsule For nest construction by Blue Tits, but not Great Tits, first‐egg date (FED) and air temperature significantly affected the mass of the nest as a whole and some of its component parts. Aims To test the hypothesis that use of nest materials is influenced by prevailing climatic conditions during nest construction. Methods Nests used in the study were built by Blue Tits Cyanistes caeruleus and Great Tits Parus major in nestboxes at a site in Lincolnshire, England during the 2008 and 2009 breeding seasons. Nests were dissected into their component parts and then weighed. Results Stepwise discriminant analysis showed that the masses of grasses, feathers and bark were significantly affected by species (all higher in Blue Tits) and year significantly affected the mass of wool and dust in the nests. anova showed that total mass of the nest was not significantly affected by year of construction or species. By contrast, species, but not year, did significantly influence the masses of animal‐ and plant‐derived materials in the nest. In Blue Tit nests there were significant correlations between FED and the mass of animal‐derived material in 2008, but with plant‐derived material in 2009. There were significant correlations between mean air temperature recorded during the seven days up to FED and the mass of the nests and their plant‐derived materials. No significant correlations were observed between FED and nest components for Great Tits. Conclusion Nest construction is potentially affected by a variety of environmental factors, which may impact upon how nests function. A better understanding of how nest variability affects its function may allow better assessment of how climate change may impact upon the reproductive performance of birds.

Local temperature and not latitude determines the design of Blue Tit and Great Tit nests

Recent studies are documenting the extent to which the mass and construction of bird nests varies between individuals and locations. In the Blue Tit (Cyanistes caeruleus) and Great Tit (Parus major), temperatures experienced by females during nest construction are inversely related to nest mass. Moreover, Mainwaring et al. (Journal of Biogeography, 2012) showed that nests constructed at high latitude are heavier and better insulated than nests built by conspecifics in the south. Although mean spring temperature was used as a proxy for latitude in the Mainwaring et al. study, it remains untested whether individual birds build nests in response to a narrower range of temperatures experienced at the start of the breeding season. Our study showed that irrespective of latitude nest mass, and in particular nest cup mass, of Blue Tits and Great Tits was significantly affected by the temperature experienced by the birds for the seven days preceding clutch initiation. Similar results were seen with the insulatory properties of nests. The potential impact of variation in nest construction and insulation on subsequent incubation and chick-rearing behaviour is discussed.

Adaptive latitudinal variation in Common Blackbird Turdus merula nest characteristics

Nest construction is taxonomically widespread, yet our understanding of adaptive intraspecific variation in nest design remains poor. Nest characteristics are expected to vary adaptively in response to predictable variation in spring temperatures over large spatial scales, yet such variation in nest design remains largely overlooked, particularly amongst open-cup-nesting birds. Here, we systematically examined the effects of latitudinal variation in spring temperatures and precipitation on the morphology, volume, composition, and insulatory properties of open-cup-nesting Common Blackbirds’ Turdus merula nests to test the hypothesis that birds living in cooler environments at more northerly latitudes would build better insulated nests than conspecifics living in warmer environments at more southerly latitudes. As spring temperatures increased with decreasing latitude, the external diameter of nests decreased. However, as nest wall thickness also decreased, there was no variation in the diameter of the internal nest cups. Only the mass of dry grasses within nests decreased with warmer temperatures at lower latitudes. The insulatory properties of nests declined with warmer temperatures at lower latitudes and nests containing greater amounts of dry grasses had higher insulatory properties. The insulatory properties of nests decreased with warmer temperatures at lower latitudes, via changes in morphology (wall thickness) and composition (dry grasses). Meanwhile, spring precipitation did not vary with latitude, and none of the nest characteristics varied with spring precipitation. This suggests that Common Blackbirds nesting at higher latitudes were building nests with thicker walls in order to counteract the cooler temperatures. We have provided evidence that the nest construction behavior of open-cup-nesting birds systematically varies in response to large-scale spatial variation in spring temperatures.

Importance of nest type on the regulation of humidity in bird nests

Nest humidity is a function of how water vapour is retained within the nest. Previous analysis suggested that in general, nest humidity was largely unaffected by ambient humidity but there was no consideration of the type of nest involved. This study examined data collected from the literature to test the hypothesis that the relationship between nest and ambient humidity is a function of the type of nest. Data for water vapour pressure for the egg (PE), nest (PN) and ambient air (PA) were collected for 48 examples of nests from 44 species of bird from a range of Orders. Initial egg mass and water vapour conductance of the eggshell was also recorded for each species. Analysis showed that birds on scrape nests are able to raise PN above PA by on average 5 Torr irrespective of PA. By contrast, PN in cup nests was unaffected by PA, such that at low values nests are well insulated against water vapour loss. The balance between the proportion of water vapour lost from the egg to the ambient air that is controlled by the nest varied with the type of nest and PA. For eggs in scrape nests mass specific water vapour conductance showed a positive relationship with PA. By contrast, for eggs in cup nests the relationship was negative and under conditions of low PA the high PN means that mass specific shell conductance values have to be high so as to ensure the appropriate rate of weight loss from the egg. Whilst birds do not control nest humidity directly the inter-relationship between weight loss from an egg, its initial mass, its shell conductance, and the incubation period can now be extended to include the water vapour conductance of the nest wall.

Egg shape changes at the theropod-bird transition, and a morphometric study of amniote eggs

The eggs of amniotes exhibit a remarkable variety of shapes, from spherical to elongate and from symmetrical to asymmetrical. We examine eggshell geometry in a diverse sample of fossil and living amniotes using geometric morphometrics and linear measurements. Our goal is to quantify patterns of morphospace occupation and shape variation in the eggs of recent through to Mesozoic birds (neornithe plus non-neornithe avialans), as well as in eggs attributed to non-avialan theropods. In most amniotes, eggs show significant deviation from sphericity, but departure from symmetry around the equatorial axis is mostly confined to theropods and birds. Mesozoic bird eggs differ significantly from extant bird eggs, but extinct Cenozoic bird eggs do not. This suggests that the range of egg shapes in extant birds had already been attained in the Cenozoic. We conclude with a discussion of possible biological factors imparting variation to egg shapes during their formation in the oviduct.

Embryonic growth and antioxidant provision in avian eggs

Avian embryos undergo extremely rapid development over a relatively short period of time, and so are likely to suffer high levels of oxidative damage unless this is mitigated by sufficient maternal allocation of appropriate antioxidants. At a species level, it is therefore predicted that antioxidants should be allocated to eggs according to the rate of embryonic growth, such that eggs containing embryos that grow faster are furnished with higher antioxidant levels, independent of egg size. We tested this prediction for three potentially important classes of dietary-derived yolk antioxidants: carotenoids, vitamin E and vitamin A. Across species, we found positive relationships between embryonic growth rate and total yolk levels of each of the three antioxidant classes. Moreover, there were consistent differences in antioxidant provision between pairs of species that share a common initial egg mass yet have differing rates of embryonic growth, such that the eggs of the faster-developing species have higher levels of carotenoids and vitamin E. These results may explain the marked interspecific variation in antioxidant provision and provide evidence for the role that these antioxidants play during embryonic development.

The impact of egg incubation temperature on the personality of oviparous reptiles

Personality traits, defined as differences in the behavior of individual animals of the same species that are consistent over time and context, such as ‘boldness,’ have been shown to be both heritable and be influenced by external factors, such as predation pressure. Currently, we know very little about the role that early environmental factors have upon personality. Thus, we investigated the impact of incubation temperature upon the boldness on an oviparous reptile, the bearded dragon (Pogona vitticeps). Eggs, from one clutch, were incubated at two different average temperatures within the normal range. After hatching the lizards were raised under the same environmental conditions. Novel object and novel environment tests were used to assess personality. Each test was repeated in both the short term and the long term. The results revealed that incubation temperature did impact upon ‘boldness’ but only in the short term and suggests that, rather than influencing personality, incubation temperature may have an effect on the development of behavioral of oviparous reptiles at different stages across ontogeny.

Evolution of parental incubation behaviour in dinosaurs cannot be inferred from clutch mass in birds

A recent study proposed that incubation behaviour (i.e. type of parental care) in theropod dinosaurs can be inferred from an allometric analysis of clutch volume in extant birds. However, the study in question failed to account for factors known to affect egg and clutch size in living bird species. A new scaling analysis of avian clutch mass demonstrates that type of parental care cannot be distinguished by conventional allometry because of the confounding effects of phylogeny and hatchling maturity. Precociality of young but not paternal care in the theropod ancestors of birds is consistent with the available data.

OPPORTUNISTIC USE OF A WOOL-LIKE ARTIFICIAL MATERIAL AS LINING OF TIT (PARIDAE) NESTS

Abstract. The lining material is a key element of bird nests, serving primarily as insulation for the adult, eggs, and/or chicks, but collection of such material has an energetic cost. Our study investigated the nest-building effort of four species of tit (Paridae) in an English wood by quantifying the use of colored wool-like artificial material in nest lining from 2000 to 2010. We recorded the distances that birds carried the material from source to nest for each nest as an indirect measure of the energetic cost of collecting nest material to individual birds. Birds did not always use nest material from the nearest source to their nest, and some birds collected material from two, three or four well-separated sources. There was no detectable color preference in choice of material, and few birds traveled more than 200 m to gather the material. Use of the material appeared to depend on the species. Within defined areas around material dispensers not all individual Great Tits (Parus major) used the artificial material, and, for all species examined, the proportion of birds using the material declined with increasing distance between source and nest. Use of artificial material suggested that selection of nest materials was probably opportunistic but also reflected the preference of these species for a wool-like nest lining.