Bill Dimensions Research Articles

Melospiza melodia (Song Sparrow) bill size is primarily shaped by thermoregulation on the California Channel Islands

ABSTRACT Inferring the environmental selection pressures responsible for phenotypic variation is a challenge in adaptation studies as traits often have multiple functions and are shaped by complex selection regimes. We provide indirect evidence that morphology of the multifunctional avian bill is primarily shaped by climate and thermoregulatory ability in Melospiza melodia (Song Sparrow) on the California Channel Islands. Our research builds on a study in M. melodia museum specimens that demonstrated a positive correlation between bill surface area and maximum temperature, suggesting a greater demand for dry heat dissipation in hotter, xeric environments. We sampled contemporary sparrow populations across 3 climatically distinct islands to test the hypotheses that bill morphology is influenced by habitat differences with functional consequences for foraging efficiency and is related to maximum temperature and, consequently, important for thermoregulation. Measurements of >500 live individuals indicated a significant, positive relationship between maximum temperature and bill surface area when correcting for body size. In contrast, maximum bite force, seed extraction time, and vegetation on breeding territories (a proxy for food resources) were not significantly associated with bill dimensions. While we cannot exclude the influence of foraging ability and diet on bill morphology, our results are consistent with the hypothesis that variation in M. melodia need for thermoregulatory capacity across the northern Channel Islands selects for divergence in bill surface area.

Do foraging methods in winter affect morphology during growth in juvenile snow geese?

Physical exertion during growth can affect ultimate size and density of skeletal structures. Such changes from different exercise regimes may explain morphological differences between groups, such as those exhibited by lesser snow geese (Chen caerulescens caerulescens; hereafter snow geese) foraging in southwest Louisiana. In rice‐prairie habitats (hereafter rice‐prairies), snow geese bite off or graze aboveground vegetation, whereas they dig or grub for subterranean plant parts in adjacent coastal marshes. Grubbing involves considerably more muscular exertion than does grazing. Thus, we hypothesized that rates of bone formation and growth would be lower for juveniles wintering in rice‐prairies than those in coastal marshes, resulting in smaller bill and skull features at adulthood. First, we tested this exertion hypothesis by measuring bills, skulls, and associated musculature from arrival to departure (November–February) in both habitats in southwest Louisiana, using both banded birds and collected specimens. Second, we used the morphological data to test an alternative hypothesis, which states that smaller bill dimensions in rice‐prairies evolved because of hybridization with Ross's geese (C. rossii). Under the exertion hypothesis, we predicted that bill and skull bones of juveniles would grow at different rates between habitats. However, we found that bill and skull bones of juveniles grew similarly between habitats, thus failing to support the exertion hypothesis. Morphometrics were more likely to differ by sex or change with sampling date than to differ by habitat. We predicted that significant, consistent skewness toward smaller birds could indicate hybridization with Ross's geese, but no skewness was observed in our morphological data, which fails to support the hybridization hypothesis. Further research is needed to clarify whether snow geese wintering in Louisiana represent a single polymorphic population that segregates into individually preferred habitats, which we believe at present to be more likely as an explanation than two ecologically and spatially distinct morphotypes.

Evolution of island warblers: beyond bills and masses

In this paper, we take a closer look into the evolution of Acrocephalus warblers on islands in the Atlantic, Indian and Pacific Oceans. The shape‐related morphological evolution of island species is characterized by changes in the hind limb, flight, and feeding apparatus. Birds on islands converged to a morphology with strong legs, shorter rictal bristles, and rounder, more slotted and broader wings. Because of their high variance among islands, body size and bill dimensions did not contribute to the separation of continental and island forms, although bills tend to be longer on islands. The wings of island birds hardly vary among islands, unsurprisingly due to a lack of the adaptive features associated with long distance flights. The tendency towards shorter rictal bristles in the island warblers can be explained by the diminished role of aerial feeding, and closer contact with various substrates in the course of extractive foraging. The shift towards stronger legs in several insular species is remarkable because reed warblers on continents have even stronger legs than other passerines of comparable size. This trait correlates with diverse, acrobatic feeding techniques that are typically associated with broad habitat use. Bills reach extreme lengths on some islands. However, short bills occur as frequently, rendering this character highly variable among islands. Short bills indicate gleaning feeding techniques, whereas long bills are typical for species that pursue hidden and difficult‐to‐access prey. Body sizes differ greatly from island to island. On average, the sizes of island birds do not differ from continental ones, however. We suggest that vegetation clutter is the major driving force for this variation.The main conclusion following from our results is that evolution on islands pertains to all functional complexes, and not only the hitherto studied body size and bill dimensions.

Morphometric characterization of local geese in the Valley of Kashmir

An extensive study was carried out in the geese rearing areas of Kashmir Valley to record the morphometric parameters which included external body measurements and visceral measurements of local geese. Among the external body measurements, body weight, bill dimensions, knob diameter, neck dimensions, length from tip of bill to tail tip and wing span was significantly more in males than females. Among the visceral measurements, only jejunum length showed a significant difference between the sexes. In females, the mean oviduct length was 38.5±8.5 cm and the mean weight of ovaries was 12.51±2.225 g. In males, left testicle was found significantly larger than the right one in terms of length and breadth but the weight of left and right testicle did not vary significantly.

Fluctuating viability selection on morphology of cliff swallows is driven by climate

The extent to which fluctuating selection can maintain evolutionary stasis in most populations remains an unresolved question in evolutionary biology. Climate has been hypothesized to drive reversals in the direction of selection among different time periods and may also be responsible for intense episodic selection caused by rare weather events. We measured viability selection associated with morphological traits in cliff swallows (Petrochelidon pyrrhonota) in western Nebraska, USA, over a 14-year period following a rare climatic event. We used mark-recapture to estimate the annual apparent survival of over 26000 individuals whose wing, tail, tarsus and bill had been measured. The fitness functions associated with tarsus length and bill dimensions fluctuated depending on annual climate conditions on the birds' breeding grounds. The oscillating yearly patterns may have slowed and occasionally reversed directional change in trait trajectories, although there was a trend over time for all traits except tarsus to increase in size. The net positive directional selection on some traits, despite periodic climate-associated fluctuations, suggests that cliff swallow morphology in the population is likely to keep changing and supports recent work contending that selection in general does not fluctuate enough to be an effective driver of stasis.

Oystercatchers' Bill Shapes as a Proxy for Diet Specialization: More Differentiation than Meets the Eye

Eurasian Oystercatchers Haematopus ostralegus ostralegus are a classic example of individual feeding specialization. Feeding specialization causes morphological differentiation in Oystercatchers' bill shapes due to varying degrees of abrasion associated with specific handling techniques for each prey species. Consequently, the Oystercatcher's bill shape has been used as a proxy for diet specialization, as it provides a quick and easy way to assess the diet choice of this marine top-predator. However, bill shapes of Oystercatchers are categorized visually in distinct types, while it has been argued that the relevant variation is continuous. Also, it is unclear how comparable the bill-shape classification is among studies and between the sexes and how universal bill shape-diet relationships are. Here we investigate the usefulness of bill-shape types as a proxy for diet choice in Oystercatchers, using four new and two published datasets. We show that quantitative bill-morphometrics provide no evidence that bill-shape types are discrete entities. Additionally, the dimensions of the same bill-shape type differ across studies. This difference is unlikely to be caused by methodology and might reflect subtle additional feeding specialization among birds with the same bill-shape type. Moreover, we show that the tip of the bill of males is typically 7% higher than that of females with the same bill-shape type. A higher — and probably stronger — bill tip in males may explain why males had more shellfish in their diet than females with the same bill-shape type. Finally, a literature-review shows that the exact bill shape-diet relationship differs between studies and the sexes. We conclude that the interpretation of bill-shape type as a proxy for diet choice in Oystercatchers is context dependent. We propose that quantitative bill dimensions are a better proxy for feeding specialization than bill-shape types.

Ecological constraints on the evolution of avian brains

Birds have brains that are comparable in size to those of mammals. However, variation in relative avian brain size is greater in birds. Thus, birds are ideal subjects for comparative studies on the ecological and behavioral influences on the evolution of the brain and its components. Previous studies of ecological or behavioral correlates in relative brain size were mainly based on gross comparisons between higher taxa or focussed on the relationships between the sizes of specific brain structures and the complexity of different tasks. Here we examine variation in dimensions of the braincase, relative overall brain size and size of its components, in reference to one general ecological and behavioral task: migration. We used data from three lineages of closely related species (14 Acrocephalines, 17 Sylvia and 49 parulid warblers). Within each group, species vary in their migratory tendencies. We found that species migrating long distances have lower skulls and smaller forebrains than resident species. We discuss four hypotheses that could explain smaller forebrain sizes, and suggest relevant taxa to use in comparative analyses to examine each of these hypotheses: Brain size is energetically constrained. Contrasts can be made not only between migrants and residents, but also between birds in habitats with high and low levels of available food. Brain size is developmentally constrained; birds with short growing periods should have smaller forebrains. Comparisons need to be made between birds living in habitats with long and short breeding seasons. Bill adaptations for foraging constrain braincase dimensions. Further analyses would need to be done on groups with high variation in bill dimensions and foraging modes. Birds with small brains have to migrate to compensate for low behavioral flexibility. Contrasts between members of families containing tropical residents and migrants need to be made. We also raise the question of whether only those parts of the brain are reduced that are most dispensable and whether brain size reduction limits foraging skills and social competence.

Energy Allocation and Postnatal Growth in Captive Elegant Tern (Sterna Elegans) Chicks: Responses to High-Versus Low-Energy Diets

AbstractEffects of variable energy intake on chick growth, organ development, and gut-passage time in seabirds were investigated by raising Elegant Tern (Sterna elegans) chicks in the laboratory on three diets involving a major prey species, northern anchovy (Engraulis mordax), and a minor prey species, topsmelt (Atherinops affinis). Anchovies are ∼25% higher in energy content than topsmelt and represent a more abundant but highly fluctuating prey resource. Chicks were raised from age 15 to age 35 days posthatch on one of three diets (n = 8): (1) high-energy anchovy at the average daily intake rate, (2) low-energy topsmelt at the same intake rate, and (3) high-energy topsmelt (i.e. at a biomass equal in energy content to the anchovy diet). Chicks raised on the high-energy anchovy diet had a significantly faster gain of body mass and wing length. All three groups, however, had attained a statistically similar wing length at 35 days posthatch and did not differ in lean dry mass or pectoral muscle mass, indicating that energy was allocated preferentially toward wing development and flight capacity. Most digestive organs were heavier and gut-passage rates faster for chicks fed topsmelt. Bill dimensions and tarsus length showed little difference among chicks on the three diets. Lipid content of chicks that were fed anchovy was twice that of those fed low-energy topsmelt and one-third higher than that of chicks on the high-energy topsmelt diet. Our results indicate that Elegant Terns have evolved certain capacities for growth and digestion in response to variable prey quality that may increase the probability of chick survival. Nevertheless, if Elegant Tern chicks were switched to a lower quality, primarily topsmelt diet, they would be underweight at fledging with heavier digestive organs, lower lipid reserves, and faster gut-passage times, which would place added provisioning demands on the parents. Under that scenario, the prospects for survival and long-term reproductive success might diminish for such an Elegant Tern colony.

A method for determination of gender from bill measurements in Otago blue penguins (Eudyptula minor)

Ability to distinguish the gender of individuals of any animal population is a useful field tool. Blue penguins (Eudyptula minor) exhibit a sexual dimorphism in bill size which has not been confirmed for any New Zealand population solely by internal anatomy. In this study, bill and head dimensions were taken from birds sexed by dissection. Measurements taken from a reference group of morphologically adult birds were used to construct equations by discriminant analysis. Those equations were applied to the bill measurements of a separate, opportunistically collected test sample, including juveniles, the gender of which was known from necropsy. We found a 15% inaccuracy in the test group, mostly derived from errors in identifying juvenile males. Removal of those individuals reduced the error to 10%. Application of the equation to 47 pairs of living birds of a monitored breeding population determined the gender wrongly for only two of 94 birds. Except for juvenile males, this method is useful for identifying gender in unselected populations of blue penguins in the field. The principle is readily applicable to other New Zealand populations.

Divergent Foraging Strategies of Two Neotropical Migrant Warblers: Implications for Winter Habitat Use

Abstract To address whether foraging strategies affect habitat-use patterns of nonbreeding warblers, I quantified foraging behavior, bill dimensions, and diet (based on regurgitation samples) of Ovenbirds (Seiurus aurocapillus) and Swainson's Warblers (Limnothlypis swainsonii) wintering in three habitats in Jamaica. Ovenbirds primarily gleaned prey from the surface of the leaf litter (95% of foraging maneuvers), resulting in a diet comprised predominantly of ants (62% of all prey items), seeds (18%), and beetles (9%). Swainson's Warblers foraged by lifting leaves (80% of foraging maneuvers), resulting in a significantly different diet dominated by beetles (39%), spiders (22%), and ants (19%). More than 60% of the regurgitation samples from Swainson's Warblers contained orthopterans and/or gecko (Sphaerodactylus goniorhynchus) bones. Averaged across all habitat types, Ovenbirds consumed ants in direct proportion to their abundance based on visual counts of arthropods. Swainson's Warblers consumed beetles more than expected based on the abundance of beetles in visual counts and Berlese funnels. The use of a diversity of habitats by Ovenbirds may be related to their ability to feed opportunistically on ants, which are a widespread, abundant, and reliable resource. In contrast, based on their foraging behavior and diet, Swainson's Warblers may be restricted to habitats with a well-developed canopy and an abundant subsurface leaf-litter fauna.

DIVERGENT FORAGING STRATEGIES OF TWO NEOTROPICAL MIGRANT WARBLERS: IMPLICATIONS FOR WINTER HABITAT USE

Abstract To address whether foraging strategies affect habitat-use patterns of nonbreeding warblers, I quantified foraging behavior, bill dimensions, and diet (based on regurgitation samples) of Ovenbirds (Seiurus aurocapillus) and Swainson's Warblers (Limnothlypis swainsonii) wintering in three habitats in Jamaica. Ovenbirds primarily gleaned prey from the surface of the leaf litter (95% of foraging maneuvers), resulting in a diet comprised predominantly of ants (62% of all prey items), seeds (18%), and beetles (9%). Swainson's Warblers foraged by lifting leaves (80% of foraging maneuvers), resulting in a significantly different diet dominated by beetles (39%), spiders (22%), and ants (19%). More than 60% of the regurgitation samples from Swainson's Warblers contained orthopterans and/or gecko (Sphaerodactylus goniorhynchus) bones. Averaged across all habitat types, Ovenbirds consumed ants in direct proportion to their abundance based on visual counts of arthropods. Swainson's Warblers consumed beetles m...

Evolutionary trends in southern African glossy starlings (Lamprotornis)

Craig, A.J.F.K. 2000. Evolutionary trends in southern African glossy starlings (Lamprotornis). Ostrich 71 (1 & 2): 244–245. In southern African six Lamprotornis species occur in savanna woodland. Locally up to five species may be sympatric, dependent on similar food sources and sharing roost sites. All are obligate tree-hole nesters. Morphological differences concern signal structures (tail length and shape, iris coloration, wing notches) rather than adaptations for feeding. There is very little sexual dimorphism, and when body size is accounted for, there are no significant inter- or intra-specific differences in bill dimensions. The long-tailed L. mevesii and L. australis are probably sister taxa, which evolved in southern Africa. L. nitens and L. acuticaudus are also likely to be southern African in origin, whereas L. chalybaeus and L. chloropterus may have evolved to the north, with their current distribution in southern Africa a consequence of later range expansion. Similar modifications of signal structures in sympatric species are evident in northern glossy starlings.

Growth of Duck Bills

We analyzed growth in length and width of bill in Mallards (Anas platyrhynchos), Pekin (Anus platyrhynchos f. domestica) and Muscovy (Cairina moschata f. domestica) Ducks with growth curve analysis. Bill growth is characterized by a relatively high proportion of growth realized prehatching and early posthatching points of inflection. Individual variability of bill measurements limits its value for estimating age. Bill width is already further developed at hatching than length, a difference that is maintained throughout the posthatching period. Consequently, bill width has a lower allometric exponent than length. This delay in development of length vs. width probably reflects overall development of the skull. Skull development is in turn closely related to brain growth, thus bill dimensions correlated with brain mass with coefficients of determination of ca. 0.9.

Natal Philopatry and Close Inbreeding in Cory's Shearwater (Calonectris diomedea)

Close inbreeding is known in several bird species, although it is seldom observed (Greenwood et al. 1978, Craig and Jamieson 1988, Gibbs and Grant 1989, Bensch et al. 1994). Inbreeding can have important evolutionary consequences because it may carry both costs and benefits to fitness (Mayr 1963, Shields 1983, Greenwood 1989). However, the seemingly low rate of inbreeding in nature may result from the fact that documenting inbreeding requires long-term monitoring of marked individuals. Colonial waterbirds are good candidates for studies of inbreeding because they often exhibit high natal philopatry (Greenwood and Harvey 1982). Moreover, long-term studies allowing individual identification and monitoring are relatively easy and widespread in this group (Wooller et al. 1992). Curiously, however, only two cases of inbreeding have been reported for colonial waterbirds: Yellow-eyed Penguin (Megadyptes antipodes; Richdale 1957), and Mute Swan (Cygnus olor; Coleman et al. 1994). Here, we report two cases of close inbreeding in Cory's Shearwater (Calonectris diomedea) documented during an 18-year study. We also consider philopatric behavior in this species and its possible relationships with inbreeding. Cory's Shearwaters are highly philopatric (Ristow et al. 1990, Thibault 1993, Borg and Cachia-Zammit 1997), breeding only on islands in the Mediterranean Sea (C. d. diomedea), and along the west coast of Africa from the Cape Verde islands (C. d. edwardsii) to the Macaronesian and Berlenga islands (C. d. borealis). The biology of this species has been well documented, and geographic variation in biometric (Massa and Lo Valvo 1986), vocal (Bretagnolle and Lequette 1990), and genetic (Randi et al. 1989, Wink et al. 1993) traits tend to confirm this extreme philopatric behavior. Methods.-Our study was conducted on the Lavezzi Islands, south Corsica (300 to 400 breeding pairs). All adults and fledglings were banded and recaptured annually between 1978 and 1996 in five subcolonies totaling 104 to 133 nests (Thibault 1993); 1,045 chicks were banded during this period. Prospecting birds also have been recaptured, albeit irregularly (but more thoroughly since 1992; see Thibault 1993). Recaptured birds were sexed using bill dimensions that have about 95% predictive power (Ristow and Wink 1980, Granadeiro 1993, Thibault 1993).

Growth of Nestling and Juvenile Platypuses (Ornithorhynchus anatinus).

Body lengths and bill dimensions were recorded from 26 nestling platypuses from various museum collections and from published records. In nestling platypuses less than 3 months old bill width was greater than length, but this was reversed in older nestlings and in juveniles of both sexes. Nestlings grew from a body length of approximately 5 cm (~ 1 week of age) to 34 cm (14-17 weeks). Comparative data on growth of captive nestlings while sparse, supported the general trends seen in nestlings collected for this study. Body lengths and weights were also recorded from 219 (113 female; 106 male) platypuses which had been captured initially as juveniles in the upper Shoalhaven River. New South Wales. Recaptures resulted in 358 separate (215 female; 143 male) records from these animals. At emergence from the breeding burrow in January/February, juvenile males were significantly larger than females. Juvenile males had a mean body length of 41.2 (S.D.± 2.8) and females 37.5 (S.D.± 2.0) cm respectively (p<O.OOI) and mean body weights of recently emerged juvenile males and females were 779 (S.D.± 127) and 588 (S.D.± 88) g (p<O.OOI). Mean lengths and weights of the emerged juveniles were significantly smaller (p<O.OOI) than those sampled as adults (weight 65-70%; length 83-87%). The wide variation in weights and lengths of juvenile individuals of both sexes at first capture may be due to different times of emergence and/or the effects of different litter sizes.

Sexual size dimorphism in red-necked phalaropes and functional significance of nonsexual bill structure variation for feeding performance.

Sexual size dimorphism is widespread in shorebirds, yet no tests of the assumption that such size dimorphism extends to functionally significant dimensions of the bill exist. This report presents tests of: (1) the assumption that sexual size dimorphism extends to the feeding structures in sexually size dimorphic bird, and (2) the hypothesis that bill-size variation influences feeding performance in Phalaropus lobatus, the red-necked phalarope. Discriminant function analysis revealed that the sexes of this species can be distinguished on the basis of five body size/bill length variables, but with low accuracy in sexing of females because of misclassification of small females as males. In the shorebird literature, the assumption is generally made that in the absence of selection to the contrary, bill size scales to body size and hence sexual size dimorphism extends to bill size. However, discriminant function analysis of measures from red-necked phalaropes failed to separate the sexes on the basis of either external or internal bill dimensions other than length. Nonetheless, internal dimensions of the upper jaw combined with exposed culmen length explained 86% of the variance in feeding performance of phalaropes; high feeding performance depends on a wide, shallow, complex internal bill structure. This study provides evidence that internal bill dimensions determine feeding performance in a manner consistent with the mechanics of surface tension transport of prey. These results suggest that some dimensions of bill size may be constrained by performance demands and demonstrate that variation in bill morphology has functional consequences. © 1996 Wiley-Liss, Inc.

Sex Determination Based on Cloacal Protuberances in the Japanese Accentor Prunella rubida.

External morphological measurements and the characteristics of cloacal protuberances were investigated to find a useful index of sexing the Japanese Accentor Prunella rubida. From 20 May to 15 June in 1989-1990 and 1992, morphological variations in eight characters were measured in known-sexed 58 males and 36 females inhabiting on the top of Mt. Norikura, Japan. The males were significantly heavier and had longer wings and tails than females, but these measurements could not be used as indexes for sexing because there was still considerable overlap. No sex-related difference in size was evident in the five skeletal elements monitored (tarsus, three bill dimensions and head length). The sharpness of the cloacal protuberance of each sex proved to be the most useful index to identify the sex of individuals. The males developed a nodular cloacal protuberance formed by the growth of the distal ends of sperm-filled ductus deferens, while the female's cloaca protruded from its original position to form a cylindrical protuberance. Because the cloacal protuberance of each sex developed only during the breeding season, its use as a characteristic for sex is confined to the breeding season. Male Japanese Accentors had a relatively large cloacal protuberance and testes compared with other passerines. It seems that these large reproductive organs are linked to the intense sperm competition predicted from this species' polyandrous or polygynandrous mating combination.

Aspekte van die anatomie, morfologie en ververing van die kroonkiewiet <i>Vanellus coronatus<i/>

Aspects of the anatomy and morphology of crowned plovers (Vanellus coronatus) collected over a period of one year at the J.B.M. Hertzog (Bloemfontein) and B.J. Vorster (Kimberley) airports were investigated. The renewal of plumage in both sexes apparently takes place mainly during the summer months. Except for some bill dimensions, all standard body measurements of adult and immature males are significantly larger than those of females. No clear seasonal pattern could be distinguished in the body and liver mass of the birds. Seasonal variations in the visible fat content of adult crowned plovers of both sexes are probably related to breeding activities and the availability of food.

Individual Variation in Fruit Choice by American Robins (Turdus migratorius)

A13STRACT.--I tested American Robins (Turdus migratorius) for individual differences in fruit consumption and preference when offered six trials of a three-way choice of white mulberry (red variety; Morus alba L.), Bella honeysuckle (Lonicera x bella), and red-osier dogwood (Cornus stolonifera Michx.) fruits. Fruit choice was examined secondarily in relation to indices of fruit quality (fruit mass, percent water, refractive index, trial date, source plant) and in relation to age, sex, and individual morphometric variation of the birds. Pooling all trials and all birds, mulberry was eaten significantly more than either honeysuckle or dogwood. Although adults differed from juveniles in body mass at capture and in relative bill dimensions, fruit choice did not vary in relation to age or sex. Also, juveniles were not more variable than adults in fruit choice. However, individual birds differed significantly in fruit choice (15 preferred mulberry, 2 preferred dogwood, 0 preferred honeysuckle), and 15 individuals were consistent in fruit choice from trial-to-trial. Indices of fruit quality changed over the course of the study. For each of the three fruit species, some variables were significantly different among individual plants, over time, or both. Some fruit-quality variables explained small but significant amounts of variation in fruit consumption (numbers of fruits eaten) and preference (number of fruit A eaten/[(number of fruit B eaten) + (number of fruit C eaten)]. Robins preferred fruits from mulberry trees that had fruits of relatively lower mass and higher refractive index. After I controlled for effects of fruit quality, trial date, and source plant in multiple regression analyses, residual consumption and preference scores still differed significantly among individuals. Residuals for mulberry and dogwood were negatively correlated, which implies a trade-off in consumption of these two fruits. Individual differences in body mass, but not in bill or wing dimensions, explained significant amounts of the variation in residual mulberry consumption and in mulberry and dogwood preference. Heavier robins tended to prefer and eat more mulberries, the largest fruit, whereas lighter robins preferred dogwood fruits, which were the smallest. Dietary diversity correlated positively with wing length. Received 26 December 1990, accepted 8 June 1991.

Patterns and Variability of Growth in the Yellow-Eyed Penguin

Growth of Yellow-eyed Penguin (Megadyptes antipodes) chicks was monitored at six breeding areas over one season, and at two breeding areas over three seasons to describe the growth pattern and determine the degree of interseasonal and interlocality variation in growth rates. Growth parameters measured were weight, bill depth, flipper area, and lengths of culmen, skull, foot, central tail feathers, wing (humerus), and flipper. Data were fitted to logistic curves which were compared using a weighted least squares technique from the Maximum Likelihood Program (Ross et al. 1980). Observed seasonal and geographical variations in growth rates were small and appeared to reflect variations in food supply. Variations in growth rates of morphometric parameters were small or absent, with few differences in final fledging size. Dimensions with invariable growth rates were those that were smaller than average at maturity. Skull and foot + claw were least variable, implying high priority in the allocation of resources during development. Foot + claw was first to reach asymptotic size, followed by wing and flipper (area and length). This pattern of growth is consistent with that of other penguin species. Feet may grow quickly to allow heat loss until the flippers can function as thermal windows. Bill dimensions did not reach adult size by the end of the fledging period.