Dietary complementation by wild birds: Considerations for field studies

Variation among arthropod taxa in the amino acid content of exoskeleton and digestible tissue

Arthropod consumption provides amino acids to invertebrates and vertebrates alike, but not all amino acids in arthropods may be digestible as some are bound in the exoskeleton. Consumers may not be able to digest exoskeleton in significant amounts or avoid it entirely (e.g., extraoral digestion). Hence, measures that do not separate digestible amino acids from those in exoskeleton may not accurately represent the amino acids available to consumers. Additionally, arthropods are taxonomically diverse, and it remains unclear if taxonomic differences also reflect differences in amino acid availability. Thus, we tested: (1) if there were consistent differences in the content and balance of amino acids between the digestible tissue and exoskeleton of arthropods and (2) if arthropod Orders differ in amino acid content and balance. We measured the amino acid content (mg/100 mg dry mass) and balance (mg/100 mg protein) of whole bodies and exoskeleton of a variety of arthropods using acid hydrolysis. Overall, there was higher amino acid content in digestible tissue. There were also significant differences in the amino acid balance of proteins in digestible tissue and exoskeleton. Amino acid content and balance also varied among Orders; digestible tissues of Hemiptera contained more of some essential amino acids than other Orders. These results demonstrate that arthropod taxa vary in amino acid content, which could have implications for prey choice by insectivores. In addition, exoskeleton and digestible tissue content differ in arthropods, which means that whole body amino acid content of an arthropod is not necessarily a predictor of amino acid intake of a predator that feeds on that arthropod.

Energy density of mesopelagic fishes from the Atlantic Ocean

Mesopelagic fishes play a central role in marine food webs linking primary consumers to top predators. In this study, measures of direct calorimetry were used to analyse the energy density (ED) of 34 mesopelagic species collected at 12 stations in the equatorial and tropical Atlantic. Mean ED ranged from 2.7 kJ g^-1 wet weight (WW) for the lanterfish Lampanyctus nobilis to 8.7 kJ g^-1 WW for the lanterfish Benthosema glaciale. This study includes species of the orders Myctophiformes and Stomiiformes and represents migrants, non-migrants and partial-migrants species. The majority of the species were grouped into the medium-energy quality category (ED from 4 to 6 kJ g^-1 ); Myctophiformes showed higher energetic values than the Stomiiformes. For the different species, the ED values were discussed in relation to spawning period and energy allocation strategies for reproduction and growth and feeding and migratory behaviour, as well as the ecoregion of study. These values will be useful for future assessment of energetic transfer between trophic levels and energetic modelling of Atlantic ecosystems.

Fleshy fruit traits and seed dispersers: which traits define syndromes?

BACKGROUND AND AIMS

Fruit traits and their inter-relationships can affect foraging choices by frugivores, and hence the probability of mutualistic interactions. Certain combinations of fruit traits that determine the interaction with specific seed dispersers are known as dispersal syndromes. The dispersal syndrome hypothesis (DSH) states that seed dispersers influence the combination of fruit traits found in fruits. Therefore, fruit traits can predict the type of dispersers with which plant species interact. Here, we analysed whether relationships of fruit traits can be explained by the DSH. To do so, we estimated the inter-relationships between morphological, chemical and display groups of fruit traits. In addition, we tested the importance of each trait group defining seed dispersal syndromes.

METHODS

Using phylogenetically corrected fruit trait data and fruit-seed disperser networks, we tested the relationships among morphological, chemical and display fruit traits with Pearson's correlations and phenotypic integration indices. Then, we used perMANOVA to test if the fruit traits involved in the analysis supported the functional types of seed dispersers.

KEY RESULTS

Morphological traits showed strong intragroup relationships, in contrast to chemical and display traits whose intragroup trait relationships were weak or null. Accordingly, only the morphological group of traits supported three broad seed disperser functional types (birds, terrestrial mammals and bats), consistent with the DSH.

CONCLUSIONS

Altogether, our results give some support to the DSH. Here, the three groups of traits interacted in different ways with seed disperser biology. Broad functional types of seed dispersers would adjust fruit consumption to anatomical limitations imposed by fruit morphology. Once this anatomical filter is sovercome, seed dispersers use almost all the range of variation in chemical and display fruit traits. This suggests that the effect of seed dispersers on fruit traits is modulated by hierarchical decisions. First, morphological constraints define which interactions can actually occur; subsequently, display and composition determine fruit preferences.

Nutrition of free-living Neotropical psittacine nestlings and implications for hand-feeding formulas

Psittacidae is one of the most endangered families of birds in the world. Knowledge of their nutrition is important for understanding their survival and productivity in the wild, as well as for their adequate husbandry under human care. Hand-rearing is a common practice for psittacines, however research on their nutrition is limited. We analysed the predicted metabolisable energy, crude protein, crude fat, minerals and the essential amino acid profiles of the crop contents from free-living nestlings of scarlet macaws (Ara macao) and red-and-green macaws (Ara chloropterus) from southeastern Peru, Cuban Amazons (Amazona leucocephala bahamensis) from the Bahamas, lilac-crowned Amazons (Amazona finschi) from northwestern Mexico and thick-billed parrots (Rhynchopsitta pachyrhyncha) from northern Mexico. The crop content of the different parrot species displayed remarkably similar nutritional profiles, considering their diversity in habitats, geographic ranges and food sources. The crude protein and crude fat concentrations in crop samples were particularly similar for the Ara and Amazona species, while the thick-billed parrot stood out for its higher crude fat and lower crude protein content. Wider variations were found among the concentrations of sodium (Na) and iron (Fe), proline and tryptophan. Compared with the requirements of 6-12 weeks leghorn chickens, all free-ranging parrot diets contained lower crude protein, calcium (Ca), potassium (P) and Na concentrations. The hand-feeding formulas contained lower crude fat, magnesium (Mg), arginine, valine and phenylalanine concentrations, as well as much higher levels of Ca and zinc (Zn), in comparison with parrot crop samples. Our data suggest that a single formulation could be used to hand-rear Ara and Amazona sp. of 3 weeks of age and older, while a different formulation would likely be more appropriated for Rhynchopsitta sp. Experimental studies should evaluate if increasing the concentration of crude fat, Mg, arginine, valine and phenylalanine enhances psittacine chick growth and health.

Digestive efficiency of Knysna and purple-crested turacos fed varying concentrations of equicaloric and equimolar artificial fruit

Avian frugivores have been somewhat poorly studied with regards to the effects that different fruit sugar types and concentrations have on their digestive efficiencies. Therefore, two relatively large South African frugivores, the Knysna turaco (Tauraco corythaix) and the purple-crested turaco (Gallirex porphyreolophus), were fed artificial fruit that contained equicaloric and equimolar concentrations of different sugars, to determine their daily food and energy intake, digestive efficiencies and digestive transit times. The artificial fruit contained 6.6, 12.4 or 22%, or 0.42, 0.83 or 1.66 mol l–1 sucrose or glucose. Food intake of both turaco species increased with decreasing sugar concentration and molarity, irrespective of sugar type, suggesting compensatory mechanisms for energy requirements. Apparent assimilation efficiencies of both turaco species ranged from 61.4-90.0% and 60.2-92.4% for equicaloric and equimolar artificial fruit diets, respectively. Digestive transit times for both turaco species were slowed with an increase in sugar concentration and molarity, irrespective of sugar type. Consequently these two frugivores appear to be tolerant of sugar type and would be expected to select fruits based on energy yields. Future studies of the composition of indigenous forest fruit sugars may give insight into food preferences of the turaco species and their role as potential seed dispersers of fruiting tree species.

Birds select conventional over organic wheat when given free choice

BACKGROUND

Global demand for organic produce is increasing by euro4 billion annually. One key reason why consumers buy organic food is because they consider it to be better for human and animal health. Reviews comparing organic and conventional food have stated that organic food is preferred by birds and mammals in choice tests.

RESULTS

This study shows the opposite result-that captive birds in the laboratory and wild garden birds both consumed more conventional than organic wheat when given free choice. There was a lag in preference formation during which time birds learnt to distinguish between the two food types, which is likely to explain why the present results differ from those of previous studies. A further experiment confirmed that, of 16 potential causal factors, detection by birds of consistently higher levels of protein in conventional seeds (a common difference between many organic and conventional foodstuffs) is the likely mechanism behind this pattern.

CONCLUSION

The results of this study suggest that the current dogma that organic food is preferred to conventional food may not always be true, which is of considerable importance for consumer perceptions of organically grown food.

Within population variation and interrelationships between morphology, nutritional content, and secondary compounds of Rhamnus alaternus fruits

•  We studied within-species variation in and interrelations among morphological and chemical traits of ripe Mediterranean buckthorn ( Rhamnus alaternus ) fruit, a bird-dispersed species. •  Principal component analysis revealed that larger fruits tended to be relatively rich in nonstructural carbohydrates (NSC), water and P but poor in protein and most minerals. Small fruits tended to be relatively rich in protein, structural carbohydrates, K and Zn while intermediate size fruits tended to be rich in lipids, Mg and Ca. Variation in chemical traits (organic compounds and minerals) was typically much higher than in morphological traits (e.g. fruit size) with the exception of NSC and water content, which varied little. This discrepancy might be explained by differences in environmental conditions between plant microsites that imposed greater variability on fruit nutrient composition than on fruit-morphological traits; and by lower selective pressure by birds on fruit chemical traits than on morphological traits. •  Secondary metabolite (emodin) concentration was positively correlated with concentrations of NSC, supporting the nutrient/toxin titration model, which predicts that high levels of secondary metabolites in fruits should be off set by high nutritional rewards for dispersers. •  Emodin concentration in leaves was much higher than in fruit pulp, which may indicate its differential adaptive roles in seed dispersal and against herbivores.

Dietary amino acid complementation as a foraging strategy for wild birds

Foraging birds finding foods containing protein of various quality could satisfy their amino acid needs by either 1) choosing only those foods that contain a suitable array of essential amino acids, or 2) choosing foods in amounts that permit complementation of constituent amino acids. We studied the abilities of sparrows (Zonotrichia leuchophrys gambelii) to use dietary amino acid complementation as a foraging strategy. We conducted two series of tests: 1) to determine if sparrows could select adequate portions from food pairs in order to compensate for reciprocal dietary deficiencies of either valine and lysine or lysine and threonine, and 2) to evaluate to what extent fortuitous (passive) complementation of dietary amino acids was constrained in sparrows by the magnitude of the dietary amino acid deficiency and the schedule of daily intakes of complementary foods. Small birds appear to have limited abilities to actively exploit dietary amino acid complementation. Birds offered a choice of two foods deficient in either lysine, valine, or threonine but of complementary compositions, reduced their daily intakes of food and body masses, but to a lesser extent (ca. one-half to one-third, and ca. one-quarter as much, respectively) than when either of the deficient foods were offered alone. Even passive complementation of dietary amino acids was severely constrained by both the magnitude of the dietary amino acid deficiency and the time course of feeding. The greater the amino acid deficiency, the less effective the complementation of dietary amino acids. The time course for effective and efficient complementation of dietary essential amino acids in these small, metabolically active animals was less than 2 h.