Virginia Morandini

Sibling aggression and brood reduction: a review

Siblicide may be “facultative” or “obligate”. When food resources provided by the parents are insufficient to rear a whole litter successfully, dominants may kill their subordinate siblings, either directly by physical damage, or indirectly through enforced starvation. This phenomenon is termed “facultative siblicide” and occurs in a wide range of bird species and at least one mammalian species. In contrast, when the lowest ranking sibling is routinely killed by its dominant brood mate or littermate this is called “obligate siblicide”, and seems to affect in particular large, long-lived species characterized by intense competition for breeding sites. This “obligate siblicide” has intrigued researchers for decades, trying to find an evolutionarily satisfactory explanation for this extreme behaviour. We review all scientific literature concerning sibling aggression published in the last 66 years. A bibliography search resulted in 104 references during the last 66 years, where birds represented 88% of the total published papers. Eleven hypotheses have been formulated for explaining these results, finding that siblicide is a complicated behaviour not controlled only for parents or chicks or environmental changes, but for a whole range of factors. These hypotheses have been identified and discussed according to actual supporting data. The relationship between food resources and brood reduction was widely documented; a sustained increase in food availability led to a highly significant decrease in both frequency and intensity of aggressiveness of the older chick towards its younger sibling in facultative species, also finding similar results in obligate siblicidal species. These results would suggest siblicide is an adaptive behaviour. This review tends to show that there is probably more than a single cause behind this behaviour. We conclude that more aspects must be considered in the design of future studies in order to understand the potential evolutionary sense of aggressive behaviour among siblings, especially those concerning food allocation decisions by parents.

Using manipulation of density-dependent fecundity to recover an endangered species: the bearded vulture Gypaetus barbatus as an example

1. Endangered species subjected to reintroduction programmes often occur as small and isolated populations with local high density and depressed fecundity. Variation in territory quality may lead to this low fecundity owing to increasing occupation of suboptimal territories as population density grows, known as the habitat heterogeneity hypothesis (HHH). In this context, food supplementation in poor territories may be used to produce extra young which could be allocated to reintroduction programmes. 2. We analyse the density-dependent fecundity pattern and the underlying mechanism in a small population of bearded vultures Gypaetus barbatus in Aragon (northeast Spain). We then use population simulations to examine the viability of a hypothetical reintroduction programme using extra young produced by supplementary feeding on poor-quality territories and the effect on the donor population. We also compare the economic cost of such a reintroduction programme in relation to the cost of a traditional captive breeding programme. 3. The wild population showed clear negative, density-dependent fecundity regulation driven by the HHH mechanism. Simulations showed that extractions for translocations had no relevant long-term effects on the donor population viability, but a marked population reduction during the extraction period. However, the implementation of supplementary feeding to produce extra young for translocation lessened significantly this expected initial population reduction. 4. Analyses showed that the annual budget of a captive breeding programme for this species could be seven times more expensive than the translocation of extra young produced by food supplementation. 5. Synthesis and applications. Reintroduction programmes based on translocation of wild-reared individuals, after a supplementary feeding programme oriented to poor-quality territories, provide a source of young at least seven times cheaper than those from captive breeding programmes. The use of this approach would decrease initial effects on donor population avoiding public criticism. Increasing the number of young released during the first years of the reintroduction decreases total financial cost and increases the final population size in the new area.

Juvenile dispersal behaviour and conspecific attraction: an alternative approach with translocated Spanish imperial eagles

The transient stage prior to definitive recruitment, known as juvenile dispersal, is thought to be under great evolutionary pressure and subject to a trade-off between associated costs and long-term benefits for fitness. Conspecific attraction has been shown to be an adaptive mechanism driving dispersal behaviours that may lead to negative density-dependent dispersal patterns. However, conspecific attraction can be scarcely discernible from imprinting to the natal area in wild populations. Reintroductions in the absence of settled individuals can be used as alternative colonization-like contexts to investigate the relative role of conspecific attraction in juvenile dispersal behaviours. We examined the spatiotemporal development of dispersal movements in reintroduced juveniles of a long-lived species with deferred maturity, the Spanish imperial eagle, Aquila adalberti , in comparison with nonmanipulated juveniles from a nearby population. We found that reintroduced birds started dispersal earlier and were initially more philopatric, probably encouraged by the advantageous competitive environment in the release area. Conversely, they revealed a more expansive strategy as they matured and approached the time when settlement decisions would be made, especially in females. They returned less frequently, increased exploratory movements and dispersal ranges, and visited breeding areas, probably as a consequence of the relatively lower reproductive prospects in the release area than in nearby populations. Therefore, the singular social cueing in reintroductions may eventually lead to juvenile wandering behaviours characteristic of colonization contexts in this territorial long-lived species. Such dispersive strategies relying on conspecifics may have important consequences for population dynamics and management. They may hinder the initial settlement phase in reintroductions, although behaviours such as longer returns may enhance recruitment prospects. Translocation programmes should consider specific dispersal scenarios, as well as postrelease monitoring to increase philopatry and success probabilities.

Natural expansion versus translocation in a previously human‐persecuted bird of prey

Abstract Many threatened species in Europe have been expanding their distributions during recent decades owing to protection measures that overcome historical human activity that has limited their distributions. Range expansion has come about via two processes, natural expansion from existing range and reintroductions to new ranges. Reintroductions may prove to be a better way to establish populations because individuals are less subject to competitive relationships lowering breeding success than individuals expanding from existing populations. Whether this is true, however, remains uncertain. We compared success of breeding pairs of an expanding and a reintroduced population of spanish imperial eagles monitored for over 15 years in the south of Spain. We found significant differences in productivity between breeding pairs of each population. Newly established territories in reintroduction areas were almost three times more productive than new territories established as individuals expanded out from an existing population. We conclude that among these eagle populations reintroduced to new areas may fare as well or better than individuals expanding out form existing populations.

Factors affecting plasma chemistry values of the black-browed albatross Thalassarche melanophrys

Blood chemical reference values and variations in them in long-lived endangered birds are of metabolic, veterinary, ecological and/or taxonomic interest. In the present study, we for the first time provide such reference values and test the influence of sex, age, and nest location on up to 11 plasma values in nesting black-browed albatrosses (Thalassarche melanophrys) that we sampled in 2015 on the Falkland Islands. Our results showed that differences between sexes were not significant for any of the parameters for which we tested. We found insignificant differences in metabolically related parameters in nestlings being raised in the middle of nesting colonies and those being raised at the edges of the colonies indicating that nest location did not affect the nutritional status or health of young, developing albatrosses. Conversely, age had a significant effect on a number of metabolites, inorganic ions and enzymatic activity. In particular, age-related differences in glucose, triglyceride, urea, and uric acid suggested that the relative metabolic rate was higher in nestling than in adult albatrosses.

Sex Determination by Morphological Measurements of Black-Browed Albatrosses ( Thalassarche melanophrys ) Using Discriminant Analysis

Abstract. To provide an easy and reliable work tool to identify the sex of individuals, adult Black-browed Albatrosses (Thalassarche melanophrys) (n = 31) were weighed and measured, and the sex determined using DNA analyses. Stepwise discriminant analysis showed upper bill depth and weight to be the best predictor variables for sex determination. This model classified correctly 95.0% of the males and 81.8% of the females (overall success was 90.3%). Additionally, a single measure discriminant analysis of upper bill depth was developed that is able to separate sexes using a threshold upper bill depth of 29.87 mm, with values above this point being males and values below it being females.

Productivity is related to nest site protection and nesting substrate in a German Osprey population

AbstractThe Osprey (Pandion haliaetus) is an emblematic example of conservation. Currently, the species is progressively recovering in population size and range after dramatic reductions as a consequence of human persecution and the use of pesticides in the nineteenth and twentieth centuries. Here, we analysed the population trend and productivity in relation to the nesting substrate (artificial structures or trees) and the protection status of the nest location (inside or outside protected areas) in the eastern German population of Ospreys. The Osprey population steadily grew during the study period (2000–2009), accompanied by the increased use of artificial structures for nesting, possibly due to the scarcity of suitable natural nest sites in the region. Pairs nesting in trees showed higher variance in productivity than those nesting on artificial supports during the study period. Further, the productivity recorded in Ospreys nesting on natural sites decreased during the study period, regardless of the protection status of the nest location, whereas it did not vary for pairs nesting on artificial structures. The productivity of Ospreys was also related to the protection status of the nest location since pairs breeding inside protected areas, either in natural or on artificial nest sites, showed higher productivity than pairs nesting outside protected areas. These findings suggest that the protection of the nest location and the type of substrate used for nesting are relevant factors underlying the breeding performance in this Osprey population and are therefore key to its management.ZusammenfassungReproduktion des Fischadlers hängt vom Schutzstatus der Horstumgebung und vom Nistplatztyp ab Der Fischadler (Pandion haliaetus) ist ein Wahrzeichen für erfolgreichen Artenschutz. Nach dramatischem Rückgang durch menschliche Verfolgung und Pestizide im 19. und 20. Jahrhundert stieg die Populationsgröße in den letzten Jahrzehnten wieder an, und in vielen Regionen hat sich auch das Areal vergrößert. Hier analysieren wir den Populationstrend und die Reproduktion von Fischadlern in Ostdeutschland in Abhängigkeit vom Nistplatztyp (künstliche Strukturen vs. Bäume) und dem Schutzstatus des Nistplatzes (innerhalb vs. außerhalb von Naturparks, Biosphärenreservaten und einem Nationalpark). Die Fischadlerpopulation ist im betrachteten Zeitraum 2002–2009 stetig gestiegen, wobei—wohl in Ermangelung geeigneter alter Nistbäume—zunehmend anthropogene Strukturen, vor allem Gittermasten genutzt werden. Paare, die auf Bäumen nisten, zeigen eine höhere Varianz in der Zahl der Nachkommen als Paare, die auf künstlichen Strukturen nisten. Die Reproduktion der Fischadler auf natürlichen Nistplätzen hat im Verlauf der Untersuchungszeit abgenommen, unabhängig vom Schutzstatus der Umgebung. Dagegen hat sich Reproduktion der Fischadler auf künstlichen Strukturen nicht verändert. Paare innerhalb von Schutzgebieten hatten eine höhere Produktivität als Paare außerhalb von Schutzzonen, egal ob auf natürlichen oder künstlichen Nistplätzen. Die Ergebnisse weisen darauf hin, dass Schutzgebiete und der Nistplatztyp für die Reproduktion in dieser Fischadlerpopulation und ihr Management relevant sind.

Physiological conditions of parent and offspring Black-browed Albatrosses Thalassarche melanophris

ABSTRACT Capsule: In Black-browed Albatrosses Thalassarche melanophris nutritional condition is correlated between parents and their offspring. Aims: To test resource allocation hypotheses analysing the relationship between parental and offspring nutritional condition. Methods: We measured blood chemistry parameters related with nutritional condition in 24 parents and their nestlings in a colony of Black-browed Albatrosses. Results: There were no significant differences in blood parameters between sexes or location of the nest within the colony, neither among adults nor among nestlings. We found a significant positive correlation between parents and the nutritional condition of their offspring, measured as urea, uric acid and beta-hydroxybutyrate concentrations in blood. Discussion: These relationships demonstrate that condition of the young seems to be merely a reflection of parental condition. An interesting relationship between alkaline phosphatase concentration in adults and nutritional condition of their nestlings was found, suggesting that age of the parents would be a key factor explaining quality of the nestling.

Natal philopatry: local experience or social attraction? An experiment with Spanish imperial eagles

We investigated juvenile dispersal strategy of a territorial long-lived species with deferred maturity, the Spanish imperial eagle, Aquila adalberti . Here we used a reintroduction programme as an experimental approach to test separately predictions of the two hypotheses about natal philopatry: social attraction and local experience. We determined the maximum juvenile dispersal distance of 90 young eagles in three different categories: (1) 31 translocated young released without adults in the area; (2) 29 translocated young released with adults breeding in the area; and (3) 30 wild nonmanipulated individuals. No differences between the sexes were found but there was a highly significant difference between the three categories, with longer distances in young released without adults in the area and similar distances in the other two categories. Our results thus showed that social attraction determined the juvenile dispersal strategies in this species.