The snapping strength of the egg shells of various orders of birds

A study of the snapping strength (S) of egg shells and its relationship to the square of the thickness (T²) has been made on seven orders of birds and also in respect of a few shells of ratite birds, domestic fowl and guinea fowl.
There are considerable differences in strength between the egg shells of different orders of birds and when shells are snapped outwards the egg shells of Sphenisciformes are almost twice as strong as those of Podicipitiformes for a given thickness. The shells of the guinea fowl are very strong and those of the domestic fowl weak compared with the seven orders when they are snapped inwards.
Comparisons of the strength of shells with and without the outside chalky cover, which occurs on the egg shells of Sphenisciformes, Pelecaniformes and Podicipitiformes, show very variable relationships, while comparisons of inward and outward snapping strength indicate that in some orders the difference is great but that in others it is negligible.
The presence or absence of a cover on the shell could not explain any difference in snapping strength, nevertheless, a few tests on Pelecanus shells using impact strength showed that then the cover adds considerably to the strength. No other shell characteristics could explain the differences in snapping strength.     

The middle ear of the skull of birds: the Pelecaniformes and Ciconiiformes

The anatomy of the middle ear region of the skull is described for the families of the Avian orders Pelecaniformes and Ciconiiformes. Emphasis is placed on the foramina and paths of the nerves and blood vessels. The morphology of the basicranium and quadrate is also discussed. Comparative analyses of the characters are used to assess taxonomic conclusions.
Extant Pelecaniformes consist of six families, four of which are monogenic: Phaethontidae, Pelecanidae, Anhingidae and Fregatidae; one is composed of two genera: Sulidae; and the last has three genera: Phalacrocoracidae. Several years ago a relationship was suggested which would ally the Phaethontidae and the Fregatidae. While these families share several non middle ear characters the anatomy of the middle ear is not compatible with any particular relationship. Indeed, several obvious differences are described. The data presented here are consistent with the idea that the Phaethontidae and the Fregatidae each form a separate group of Pelecaniform birds, with the rest of the families forming a third group. Several differences in the middle ear region of the species of Anhingidae suggest that the family may be composed of two genera.
While sharing many Ciconiiform characters the Ciconiidae have been shown not to be as closely related to the Ardeidae as they are to other families of Ciconiiformes. In addition, evidence is presented to support the recent idea that the three species of ibis (I. ibis, I. cinereus and I. leucocephalus ) be united within the genus Mycteria. Also supported is the notion that Balaeniceps is Pelecaniform in character, and not Ciconiiform.     

EGG COMPOSITION AND HATCHLING PRECOCITY IN SEABIRDS*

This paper presents analyses of the composition (shell, yolk, albumen) and of the quality (lipid, protein and water contents) of yolk and albumen of eggs of 25 species of seabirds belonging to the Sphenisciformes, Procellariiformes, Pelecaniformes, and Lari of the Charadriiformes. These data are compared with those published for species in the same orders and suborders, and the combined seabird data are compared with published data for non-seabirds. Variation in the proportionate weight of eggshell is not related to hatchling precocity but is probably due to adaptive differences in nest substratum and the agility of the incubating birds. Lipid and protein contents of yolk, and water content of albumen, are uniform in eggs of all examined species. Protein levels of albumen and water content of yolk and of entire egg contents vary greatly between taxa. Contrary to previous claims there is no simple relationship between egg composition and hatchling precocity. Differences in egg composition will probably only be clearly understood when the nutritional needs of the embryo, and of the hatchling in the time before it regularly obtains food, are known.     

A study of the egg shells of the Falconiformes

A study of a selection of egg shells of the Falconiformes has been made similar to the earlier ones on ratites, the Anatidae and the Sphenisciformes. Chemical analyses, and histological and plastic embedding techniques were used.
The main part of the shell in all species studied consists of large crystals running through the shell. There was no layer of fine vertical crystals above this and no cover, and even the cuticle was not very pronounced. Histological studies showed no major differences, except that some shells had vacuoles in the outer layers. All such shells also gave an unetched outer layer when plastic embedded radial sections were studied and thin sections showed spaces between and within crystals. These spaces in the outer layers of the shell were of taxonomic interest for they were not present in the Cathartidae, the Falconidae and Sagittarius serpentarius.
Pore channels appeared to be much sparser than in other orders so far studied and all pores were single. Pigment was present on the surface of some shells, but it was also found in different layers of the shell right down to the cone layer and, in one case, had leaked through on to the membrane.
There were significant relationships between total and soluble shell nitrogen which divided the Falconidae from most of the Accipitridae but left Pernis and Pandion in an intermediate position.     

PHYLOGENY AND FORELIMB DISPARITY IN WATERBIRDS

Previous work has shown that the relative proportions of wing components (i.e., humerus, ulna, carpometacarpus) in birds are related to function and ecology, but these have rarely been investigated in a phylogenetic context. Waterbirds including “Pelecaniformes,” Ciconiiformes, Procellariiformes, Sphenisciformes, and Gaviiformes form a highly supported clade and developed a great diversity of wing forms and foraging ecologies. In this study, forelimb disparity in the waterbird clade was assessed in a phylogenetic context. Phylogenetic signal was assessed via Pagel's lambda, Blomberg's K, and permutation tests. We find that different waterbird clades are clearly separated based on forelimb component proportions, which are significantly correlated with phylogeny but not with flight style. Most of the traditional contents of “Pelecaniformes” (e.g., pelicans, cormorants, and boobies) cluster with Ciconiiformes (herons and storks) and occupy a reduced morphospace. These taxa are closely related phylogenetically but exhibit a wide range of ecologies and flight styles. Procellariiformes (e.g., petrels, albatross, and shearwaters) occupy a wide range of morphospace, characterized primarily by variation in the relative length of carpometacarpus and ulna. Gaviiformes (loons) surprisingly occupy a wing morphospace closest to diving petrels and penguins. Whether this result may reflect wing proportions plesiomorphic for the waterbird clade or a functional signal is unclear. A Bayesian approach detecting significant rate shifts across phylogeny recovered two such shifts. At the base of the two sister clades Sphenisciformes + Procellariiformes, a shift to an increase evolutionary rate of change is inferred for the ulna and carpometacarpus. Thus, changes in wing shape begin prior to the loss of flight in the wing‐propelled diving clade. Several shifts to slower rate of change are recovered within stem penguins.     

The phosphate-rich cover on the eggshells of grebes (Aves: Podicipitiformes)

Spheres of a nut-like morphology–a "kernel" formed from spherules contained in a "shell" of globular sub-units–were a unique feature of the cover on the eggshells of six species of the order Podicipitiformes: Red-necked grebe (Podiceps grisegend) , Great crested grebe (Podiceps cristatus) , Little grebe (Tachybaptus ruficollis) , Black-necked grebe (Podiceps nigrkollis) , Slavonian grebe (Podiceps auritus) and Pied-billed grebe (Podilymbus podiceps). The spheres did not give a pattern with X-ray diffraction; the innermost ones were embedded in the dense crystalline layer on the outer surface of the calcitic portion of the shell. Electron-probe microanalysis revealed that the cover of spheres contained principally oxygen, calcium, phosphorus and sulphur and infra-red analysis demonstrated the presence of phosphate. The outer surface of the stratum of spheres was bounded by a thin, fissured layer of amorphous material.
These observations raise questions about the ionic environment obtaining in the shell gland towards the end of shell formation and the adaptive significance of the cover on the eggshells of members of the Podicipitiformes.     

The middle ear of the skull of birds: the ostrich, Struthio camelus L.

The morphology of the middle ear region including die basicranium and quadrate of Strulhxo is very simil.n to ilic same region in the orders Procellariiformes, Pelecaniformes, Ciconiiformes and Sphenisciformes. Struthio though, has some unique middle ear characters such as die lack of a chorda tympani nerve, the arrangement of die glossopharyngeal and vagus nerve foramina, die structure in the upper neck of die external ophthalmic vein and die position of die Eustachian tube. The articulatory surfaces for the quadrate bom on die zygomatic process of the squamosal and the mandible are unique in Struthio when compared to the several orders mentioned above.     

The size, shape and orientation of pore grooves in the egg shells of Rhea sp.

In the egg shells of Rhea sp. there are grooves on the surface and it is into these grooves that one or more pore mouths open.
Five egg shells of Rhea americana and four of Rhea darwinii were studied in detail in respect of the numbers of pore mouths and the number, length and orientation of the grooves. It was found that R. americana had nearly twice as many pore mouths and grooves as had R. darwinii. Their distribution in both species showed more and longer grooves and more pore mouths in the equatorial regions than in the polar regions of the shell. The grooves were also found to be approximately longitudinally orientated in the equatorial regions but this orientation became less marked towards the polar regions. Not surprisingly longer grooves tended to have more pore mouths than did shorter grooves, but, in addition, broader grooves were associated with greater length too.     

Preferred orientation of calcite in the ratite and tinamou eggshells

Using X-ray diffractometry, the development of preferred orientation was studied in one species from each of the extant ratite families, from two moas and two tinamous and, as a preliminary comparison, from representative species from 16 of the other carinate orders. A preferred orientation begins to develop immediately after the start of shell deposition, and in all shells studied was one in which the (001) planes tend to lie parallel to the shell surface. The degree of (001) texture that develops in the ratite and tinamou shells is greater than that developed in the other carinate orders. Development in the ostrich, kiwi and tinamou is uninterrupted so that there is a very high degree of (001) preferred orientation at the exteriors of the shells. In the Emu, cassowary, rhea and the two moa species, a very high degree of (001) texture reverses gradually within the central layer of the shell, and in some species this is accompanied by the development of a very weak (104) preferred orientation. The weak (001) textures observed in the shells of the 20 species from the carinate orders other than the Tinamiformes develop slowly and without interruption through the shell; in four species a weak (104) texture develops simultaneously to that of the (001), forming a double texture similar to that already reported in the majority of shells of the domestic fowl.     

Flight behaviour of seabirds in relation to wind direction and wing morphology

We studied flight direction relative to wind direction (hereafter referred to as "flight direction"), the relation between wing morphology and flight behaviour and interspecies relationships in flight behaviour among all major seabird taxa. We calculated wing loading and aspect ratios for 98 species from 1029 specimens. Species were sorted into 13 groups on the basis of similarity in patterns of flight direction. The primary flight direction of Pelecaniformes and Charadriiformes was into and across headwinds. The most common flight direction of Procellariiformes was across wind. Seabirds avoided flying with tailwinds. Wing loading and aspect ratios were positively correlated in Procellariiformes, Pelecaniformes and alcids but negatively correlated in larids. In Procellariiformes, incidence of headwind flight and that of tailwind flight were significantly correlated with wing loading and aspect ratio; species with higher wing loading and aspect ratios flew more often into headwinds and less often with tailwinds. In contrast, the proportion of Pelecaniformes and Charadriiformes flying with tailwinds increased significantly with increased wing loading. Our results demonstrate a close link in seabirds between flight behaviour, wing morphology and natural history patterns in terms of distribution, colony location, dispersal and foraging behaviour.     

Eggshell structure, mode of development and growth rate in birds

The shell of an egg contributes to successful embryogenesis in many ways, such as through protection, respiration and water exchange. The shell is also the major source of calcium for the development of high-calcium consuming organs, e.g. the skeleton, muscles and brain. Some studies show, moreover, that growth rate may play a fundamental role in the pattern of skeletal development in birds: the faster the growth the less ossified the skeleton is at hatching. We predicted, therefore, that slow (precocial) and fast (altricial) growing bird species should lay eggs encased in shells with different structures adapted to support different rates of calcium removal by developing embryos. We tested this prediction by comparing the fine structure of the inner eggshell surface (mammillary layer) from 36 bird species belonging to 18 orders ranging from Struthioniformes to Passeriformes. Using scanning electron microscopy, we compared the mammillary layer of both non-incubated eggs and eggs at the time of hatching, i.e., before and after embryonic development and the accompanying calcium removal. The results were consistent with the prediction, i.e., the number of mammillary tips per unit of surface area was associated with mode of development and growth rate. The number was higher, and calcium removal was also more extensive, in shells from precocial bird species than in shells from altricial bird species.     

The distribution of organic cores, cones, cone junctions and pores in the egg shells of wild birds

Egg shells from 14 widely different species of wild birds were examined, using collodion casts of the inside surface of the shell. Organic cores, cones, cone junctions and pores were counted and in each case measurements of nearest neighbour distances were taken. Shell thickness was also measured.
It was found that, using mean values for each egg shell, there were highly significant, and in some cases almost perfect linear relationships between core numbers, cone numbers, cone junction numbers and pore numbers on the one hand and their respective nearest neighbour distances expressed as the reciprocal of the mean of the squares of these distances on the other. The results also showed that the distribution of all four structures was not random, but had a degree of uniformity increasing up the series pores < cone junctions < cores < cones.
The following relationships were also highly significant: core and cone numbers, core and cone junction numbers, and cone and cone junction numbers. The relationship of pore numbers to any of the other three structures was of no great significance.
Shell thickness was related curvilinearly to core numbers and to cone numbers and linearly to nearest neighbour values for cones. It was also related to pore numbers.
It is suggested that, apart from pores the other three structures and their distribution all depend upon the number of cores which are the original centres of crystallization from which the shell grows. To a lesser extent shell thickness also depends upon these structures. Tentative suggestions are also made concerning the origin of the pores.     

Chemotaxonomical relationships between penguins and tubenoses

The compositions of the uropygial gland wax of seven species of birds of the order Procellariiformes (tubenoses) belonging to four different families are compared with one another and with those of birds belonging to other orders. The results are discussed from a chemotaxonomical viewpoint. For this purpose, the various parameters have been depicted on a 3-dimensional matrix. Although all birds investigated are obviously related to each other, two of the species (Diomedea and Garrodia) also show a relationship to different orders. The results support the opinion that the Procellariiformes are closely related to the Sphenisciformes (penguins).     

The anatomy of the middle ear of the tinamiformes (Aves: Tinamidae)

The morphology of the middle ear region including the basicranium and quadrate of tinamous is compared among ratites and flying birds belonging to the Procellariiformes, Sphenisciformes, Pelecaniformes, and Ciconiiforms. The middle ears of tinamous and ratites share a number of important characters including absence of a separate foramen for the glossopharyngeal nerve; eustachian tube, carotid artery, and stapedial artery encased in bone; and a metotic process with vascular canals or notches. Outgroup analysis confirms these characters as synapomorphies. These data support the position that the Tinami and Ratiti form a monophyletic assemblage.     

Associations between gastropod shell characteristics and egg production in the hermit crab Pagurus longicarpus

Summary Two populations (salt marsh and seagrass bed) of the hermit crab Pagurus longicarpus were sampled to examine associations between shell characteristics and egg production. Multivariate statistical analyses controlled for crab size and time of year, variables that otherwise could be confounded with shell effects. Although correlations between shell characteristics and reproduction existed in both populations, generalizations could not be made because associations varied within and between populations. Shell species was not associated with a female's reproductive state (i.e., whether or not she was barren when sampled) in either population. In the seagrass population, medium-large and large females occupying severely damaged or fouled shells were half as likely to be reproductive as females occupying other shell conditions. However, there was no association between shell condition and reproductive state for small and small-medium females in the seagrass population or among all females in the salt marsh population. In the seagrass population, small through medium-large reproductive females occupied shells more similar to their predicted shell size, regardless of whether the occupied shell was relatively small or large, than nonreproductive females. In contrast, relative shell sizes of reproductive and nonreproductive females were similar for large females in the seagrass population and all females in the salt marsh population. Clutch sizes were enhanced for females occupying Polinices duplicatus shells or shells larger than their predicted shell size in the seagrass population. Relative shell size also was associated with clutch size in the salt marsh population, but crabs occupying shells similar to their predicted shell size had the largest clutches.     

Ecological factors affect the level and scaling of avian BMR

The basal rate of metabolism (BMR) in 533 species of birds, when examined with ANCOVA, principally correlates with body mass, most of the residual variation correlating with food habits, climate, habitat, a volant or flightless condition, use or not of torpor, and a highland or lowland distribution. Avian BMR also correlates with migratory habits, if climate and a montane distribution is excluded from the analysis, and with an occurrence on small islands if a flightless condition and migration are excluded. Residual variation correlates with membership in avian orders and families principally because these groups are behaviorally and ecologically distinctive. However, the distinction between passerines and other birds remains a significant correlate of avian BMR, even after six ecological factors are included, with other birds having BMRs that averaged 74% of the passerine mean. This combination of factors accounts for 97.7% of the variation in avian BMR. Yet, migratory species that belong to Anseriformes, Charadriiformes, Pelecaniformes, and Procellariiformes and breed in temperate or polar environments have mass-independent basal rates equal to those found in passerines. In contrast, penguins belong to an order of polar, aquatic birds that have basal rates lower than passerines because their flightless condition depresses basal rate. Passerines dominate temperate, terrestrial environments and the four orders of aquatic birds dominate temperate and polar aquatic environments because their high BMRs facilitate reproduction and migration. The low BMRs of tropical passerines may reflect a sedentary lifestyle as much as a life in a tropical climate. Birds have BMRs that are 30-40% greater than mammals because of the commitment of birds to an expensive and expansive form of flight.     

Effects of experimental calcium availability,egg parameters and laying order on Great Tit Parus major eggshell pigmentation patterns

Many bird species lay eggs speckled with protoporphyrin‐based spots, however, for most of them the function of eggshell spotting is unknown. A plausible hypothesis is that protoporphyrin might have a structural function in strengthening the eggshell and is therefore deposited when calcium is scarce. In this study, we experimentally provided Great Tit Parus major females with supplemental calcium to examine its effect on the protoporphyrin‐based maculation of their eggs. In addition, we studied variation in eggshell pigmentation patterns in relation to other egg parameters and laying order. Calcium‐supplemented females laid larger eggs but shell thickness was not significantly affected by the treatment. Calcium supplementation may reduce the time and energy females devote to searching for calcium‐rich material, so that they can collect more nutrients and so lay larger eggs. Furthermore, pigment darkness was associated with egg volume and shape, which suggests that female quality and environmental food availability may also influence the shell pigmentation pattern. Within clutches, later‐laid eggs had larger and darker spots that were distributed more unevenly on the shell surface. This within‐clutch pattern could be explained by the increase in egg volume and egg shape and a decline in shell thickness with egg‐laying order, which characteristics were all related to shell‐spotting pattern. Eggs with a coronal ring had thinner shells, but pigment intensity and spot size were not related to shell thickness. Thus, our results suggest that concentrated spotting distribution may have a mechanical function, supporting the structural‐function hypothesis.     

Protegulum and brephic shell of the earliest organophosphatic brachiopods

Early development stages imprinted on the shells of Cambrian brachiopods from the class Linguliformea (orders Paterinida, Lingulida, Acrotretida) were studied with scanning electron microscope based on a large collection from the Siberian Platform. Some specimens of all three orders preserved protegulum (embryonic shell); their brephic (juvenile) shells, also were studied. Many of them might lack larval development stage as it is known for the recent representatives of the family Lingulidae. But unlike recent lingulids, the surface of the juvenile dorsal valves of all studied linguliformeans bore two (rarely three) pairs of gentle elevations accommodating bundles of setae, which sometime preserve as groups of fine imprints along their margins. Recent Lingula and Glottidia lack setae in this stage. On the other hand, recent classes Craniformea and Rhynchonelliformea have setae, but they develop in the larval stage. Most of brachiopod groups have the setae in the adult stage but these setae have different origin, are short, located on the lateral and anterior ends of the shell, and grow from the marginal cells of the mantle.     

An arbitrary classification of the pore systems in avian eggshells

An arbitrary classification of the pore systems in shells has been based on the observations made during a survey with a scanning electron microscope of the eggs of c. 60 avian species. The classification is intended primarily to aid comparative studies of shell function and field studies of the overall contribution of the shell to the embryo's well-being. The location and form of the external orifice of the pore was used to define four major types of pore systems: (1) outer orifice open—the pore canal terminates at the surface of the shell; (2) outer orifice occluded—the pore canal terminates at the surface of the shell but the orifice is occluded by amorphous, waxy material; (3) outer orifice capped—the pore canal terminates at the outer edge of the true shell and its orifice is capped and, in many species, plugged by a stratum of vesicles, either organic or inorganic, which clothes the entire surface of the shell, and (4) outer orifice reticulate—the pore canal terminates at the edge of the column layer and its orifice is covered by a calcareous stratum containing a plexus of tubules. Each group was further divided on the form of the pore canals; shells having unbranched pore canals were put into one category and those in which some pores branched into another.     

Structure of shells of eggs of Callisaurus draconoides (Reptilia, Squamata, Iguanidae)

Female zebra-tailed lizards (Iguanidae: Callisaurus draconoides ) lay roughly ovoid eggs with thin, highly extensible shells. The outer surface of the eggshell is a thin, calcareous crust of calcium carbonate in the calcite morph. Immediately beneath the crystalline matrix is a shell membrane composed of multiple layers of fibres organized into an undulating series of troughs and crests, apparent in both cross-section and surface view. The outer surface of the shell membrane is differentiated into a tightly woven fibrous mat that may serve to anchor the calcareous layer to the membrane. Organization of the eggshell into a series of troughs and crests serves to increase the surface area available for contact with the substrate and, presumably, to increase the capacity of the eggshell to stretch as the egg absorbs water.