Bill Length (bill + length)

Distribution by Scientific Domains

Selected Abstracts

Variation in the growth and survival of Golden Plover Pluvialis apricaria chicks

IBIS, Issue 2 2002
J. W. Pearce-Higgins
The growth of Golden Plover Pluvialis apricaria chicks is modelled in detail for the first time. The pattern of growth is typical of postnatal development in waders, although the mean fledging time of 37 days is slower than would be expected from adult body weight. Bill length and weight at hatching had significant effects on the rate of weight gain shown by 2-day-old chicks, although this effect was not noticeable at 4 days of age. Chick survival was significantly affected by bill length, as a result of the variation in weight gain. The growth of older chicks was positively correlated with mean minimum temperature. The slow rate of growth exhibited by Golden Plover chicks is discussed in relation to breeding habitat and the effects of weather and hatchling biometrics. [source]

Lifetime reproductive success in relation to morphology in the house sparrow Passer domesticus

Henrik Jensen
Summary 1In this study we relate variation in lifetime reproductive success (LRS) of male and female house sparrows Passer domesticus to morphological characteristics. 2Our analyses demonstrated no sex-specific difference in the distribution of LRS. The variance in LRS was influenced mainly by variation in individual annual reproductive success, and to a lesser extent by variation in individual lifespan. 3Phenotypic traits explained a significant proportion of the variation in LRS in males, but not in females. The effect of male morphology on LRS operated mainly through an effect on the number of recruiting daughters. 4The size of the patch of black feathers on the chest of males (badge size) and male bill length were both positively associated with LRS. Lifespan and bill length were positively related and reproductive success increased with badge size. In females, number of recruiting daughters was positively related to bill length, body mass and body condition index due to the positive effect of these traits on annual production of daughters. 5These results indicate that identifying factors causing the large individual variation in LRS, which is likely to be closely related to fitness, will be important to understand microevolutionary processes in this metapopulation, and hence their demographic feedbacks. [source]

Using net sacks to examine the relationship between egg size and young size in Common Pochards

David Ho
ABSTRACT Investigators studying the relationship between egg size and young size often face difficulties in assigning particular young to particular eggs. We present a new method based on the use of separate net sacks for each egg that allowed us to study this phenomenon in Common Pochards (Aythya ferina) without excessive disturbance of breeding birds. We found a positive isometric relationship between duckling body mass and estimated fresh egg mass (P < 0.001). However, we found no relationship between estimated fresh egg mass and structural measurements of ducklings (tarsus and bill length, both P > 0.29). In addition, we found a weak positive relationship between estimated egg mass and the size of ducklings (P= 0.049). Greater hatchling mass typically means a larger yolk supply, and more yolk may provide energy crucial for survival during the first few days after hatching. In addition, ducklings with longer tarsi may be better swimmers and better at finding food and escaping from predators. Although our method has certain limitations and investigators should consider risks when applying it in over-water nests or in nests with large clutches, we believe it is a reliable way to assign young to particular eggs in waterfowl and possibly other bird species. SINOPSIS Los investigadores que estudian la relación entre el tamaño del huevo y el tamaño de los pichones se han encontrado con la dificultad de asignar un pichón a un huevo en particular. Presentamos un nuevo método basado en el uso individual de sacos de redes (para cada huevo), que nos ha permitido estudiar el fenómeno en Aythya ferina, sin causar gran disturbio a la reproducción de las aves. Encontramos una relación isométrica positiva entre la masa del patito y el estimado de la masa del huevo fresco (P < 0.001). Sin embargo, no encontramos una relación apropiada, entre la masa fresca del huevo y medidas estructurales en los patitos (ej. longitud del tarso y el pico, ambos con P > 0.29). Además, encontramos una relación positiva, pero débil, entre el estimado de la masa del huevo y el tamaño del patito (P= 0.049). Al eclosionar, una mayor masa del patito, significa una mayor cantidad de yema. Una mayor cantidad de esta pudiera proveer de mayor cantidad de energía la que a su vez pudiera ser crucial para la sobrevicencia durante los primeros dias. En adición, patitos con tarsos de mayor tamaño pudieran ser mejores nadadores, y más capaces de encontrar alimento y escapar de depredadores. Aunque nuestro método tiene limitaciones (y los investigadores debieran considerar el riesgo de aplicar el método en nidos sobre agua o en nidos con grandes camadas), creemos que es una forma confiable de asignar un neonato a un huevo particular, tanto a aves acuática como posiblemente a otras especies. [source]

Individual feeding specialisation in shorebirds: population consequences and conservation implications

ABSTRACT Individual feeding specialisation in shorebirds is reviewed, and the possible mechanisms involved in such specialisations. Any specialisation can be seen as an individual strategy, and the optimum strategy for any given individual will be conditional upon its specific priorities and constraints. Some specialisations are related to social status and some to individual skills. Some are also probably frequency-dependent. However, most shorebird specialisations are constrained to a large extent by individual morphology, particularly bill morphology. For example, larger birds are able to handle larger prey, and birds with longer bills are able to feed on more deeply buried prey. Sex differences in bill length are uncommon in the Charardriidae, which are surface peckers, but are common in the Scolopacidae, which feed by probing in soft substrates. Sex differences in bill morphology are frequently associated with sex differences in feeding specialisation. There is evidence that different feeding specialisations are associated with different payoffs, in which case the probability of failing to reproduce or of dying will not be distributed equally throughout the population. I consider the population consequences of such feeding specialisations, particularly the different risks and benefits associated with different habitats or diets. I also consider the way in which individuals may differ in their response to habitat loss or change. I suggest that population models designed to predict the effect of habitat loss or change on shorebirds should have the ability to investigate the differential response of certain sections of the population, particularly different ages or sexes, that specialise in different diets or feeding methods. [source]