Avian Biology Research

A method has been devised to study the nutritional role of yolk cholesterol in the development of the chicken (Gallus gallus domesticus) embryo using egg yolk replacement. Preliminary experiments revealed that 11 mL of yolk in medium-sized eggs were adequate to support embryos from 4 to 20 days of incubation, and that low levels of β-cyclodextrin (β-CD) and amyloglucosidase (AG) in yolk were tolerated by the embryo. Fresh egg yolk was treated with β-CD at 50 °C, centrifuged to remove the insoluble β-CD-cholesterol complex, and incubated with AG to degrade residual β-CD. The cholesterol content was reduced from 13.1 mg g⁻¹ in fresh egg yolk to 1.3 mg g⁻¹ in cholesterol-reduced yolk supernatant (CRYS). Yolk granules co-precipitated with the β-CD-cholesterol complex. The cholesterol concentration of CRYS supplemented with granules from fresh yolk (i.e. CRYSg) was 3.2 mg g⁻¹. When yolks of early 5-day embryos were replaced with 11 mL of CRYS, the maximum survival was 17 days of incubation. When yolks were replaced with 11 mL CRYSg, 30% of embryos survived to 20 days, a significant increase in survival compared to CRYS (P < 0.05). Sixty per cent of embryos receiving fresh yolk (yolk controls) and 83% of embryos in intact eggs (intact controls) survived to 20 days. The controls did not differ significantly (P > 0.05). Embryos in the CRYS and CRYSg groups had shorter survivals than yolk controls (P < 0.001) and intact controls (P < 0.005). These results suggest a methodological approach for investigations of egg yolk cholesterol and yolk granules in chick embryo development.

Detection of prey DNA from faecal samples is a non-invasive method being successfully applied to the dietary analysis of birds as well as other vertebrates and invertebrates. We have employed this technique to examine the significance of Horseshoe Crab eggs (Limulus polyphemus) for Dunlins (Calidris alpina), Semipalmated Sandpipers (Calidris pusilla), Least Sandpipers (Calidris minutilla) and Short-billed Dowitchers (Limnodromus griseus) during northbound migration at their major stopover area in Delaware Bay. This was accomplished through polymerase chain reaction amplification of Limulus DNA from faecal samples using new Horseshoe Crab-specific primers. We detected the consumption of crab eggs in all study species, although results suggest that eggs may be a less important food source for Least Sandpipers than for the other species. Consumption of eggs increases as the migration season progresses, implying a strong preference of birds for this resource at the end of May, when eggs are readily accessible. The results confirm the value of Horseshoe Crab eggs for migrating shorebirds in this crucial stopover area. The Limulus-specific primers we designed can be effectively used for detection of semidigested Limulus DNA from faecal samples and thus they can be employed in the dietary analysis of other predators that seasonally capitalise on Horseshoe Crabs or their eggs.

We investigated the effects of supplemental chitosan on digestibility of feed nutrients, intestinal histology and digestive enzyme activity in the pancreas, duodenum and jejunoileum in Leiothrix lutea. Sixty-four adult birds were randomly allotted to one of four dietary treatments (basal diet supplemented with 0%, 0.1%, 0.5% and 1% chitosan). The experiment lasted for 30 days, of which the last 4 days involved metabolic experiments. Compared with the control group, the addition of 0.5% chitosan enhanced the apparent metabolism rate of dry matter, metabolisable energy, crude fat and phosphorus, and decreased apparent metabolism rate of calcium; crude protein was unaffected. Compared with the control group, the villous height of the duodenum and ileum supplemented with 0.5% chitosan increased by 12.11% and 15.03%, while the crypt depth in the duodenum deepened by 6.48%. Supplemental chitosan decreased lipase and amylase activities; trypsin and chymotrypsin activities increased first and then decreased as the level of chitosan increased. These data suggest that dietary chitosan (0.5%) may improve the digestive physiology of L. lutea in captivity by increasing the apparent metabolic rate of most nutrients, improving intestinal health and enhancing digestive enzyme activity.

Three factors potentially facilitating avian urban colonisation are: (a) inherent suitability for city environments, (b) limited resource overlap with residents, achieved through resource partitioning or outcompeting residents for shared resources, and (c) behavioural flexibility permitting innovative resource exploitation. We examined the foraging ecology and nest site choice of the Noisy Miner (Manorina melanocephala) in urban parks in Melbourne, Australia to elucidate which of these three factors was likely to be instrumental in facilitating occupancy of this urban habitat by this native honeyeater. The Noisy Miner was relatively unspecialised in its nest site choice in parks, suggesting that the many suburban parks with branching eucalypts probably provide lots of suitable nest sites for this species. Park-dwelling Noisy Miners appeared to be superior competitors for food to most cohabiting bird species. They were never targets of interspecific aggression, but quite often initiated it against 16 other bird species. Most interactions were attacks and/or chases and 74% displaced the target species’ member. In Melbourne's parks, Noisy Miners foraged for invertebrates mainly: (a) in the sub-canopy on foliage, using hanging and reaching behaviours, and (b) on the ground on bark litter and grass, gleaning in a standing posture. Several cohabiting bird species also gleaned invertebrates on the ground in a similar manner, but all also commonly used other behaviours when foraging on this substrate. No cohabiting species that foraged extensively in the sub-canopy fed substantially on invertebrates there. Thus Noisy Miners could successfully inhabit Melbourne's parks apparently at least partly because: (i) nest site choice was relatively unspecialised; (ii) they flexibly exploited food resources at ground level, unlike exurban conspecifics; (iii) they aggressively dominated possible heterospecific food competitors at ground level; and (iv) they probably experienced fairly limited dietary overlap with cohabiting bird species.

The eggshells of many avian species are characterised by distinctive patterns of maculation, consisting of speckles, spots, blotches or streaks, the spatial-statistical properties of which vary considerably between (and often within) species. Understanding the mechanisms underlying the production of eggshell maculation would enable us to explore the costs and constraints on the evolution of maculation patterns, but as yet this area is surprisingly understudied. Here I present a simple model of eggshell maculation, which is based on the known biology of pigment deposition, and which can produce a range of realistic maculation patterns. In particular, it provides an explanation for previous observations of maculation heterogeneity and diversity, and allows testable predictions to be made regarding maculation patterns, including a possible signalling role.

Differences in the deposition of limited maternal resources to eggs can reflect the optimal allocation to manipulate offspring phenotype, or constraints caused by maternal condition. We examined multiple maternal substances transferred to eggs in the magpie Pica pica to test the hypothesis that certain substances represent constraint and some optimal allocation. We did this by supplementary feeding magpies prior to egg-laying and then comparing the effect of food on maternal substances in conjunction with laying order relative to a control group. Certain substances such as carotenoids, immunoglobulins and avidin responded positively to food supplementation, whereas others, such as testosterone and total protein content of eggs, did not. Immunoglobulin allocation increased with laying order in fed but not in unfed groups. Our results suggest that patterns of optimal allocation and constraint in maternally-provisioned substances co-occur within clutches. Furthermore, constraint and optimal allocation may co-occur within the same substance i.e. immunoglobulins, highlighting the complexities of maternal resource allocation.