Possible functions of alternative nests in raptors: the case of Bonelli's Eagle

Auteur(s): Diego Ontiveros, Jesús Caro, Juan Manuel Pleguezuelos
Bron: Journal of Ornithology, Online article 9 January 2008
Abstract: Four non-exclusive hypotheses have been proposed to explain the alternative nest-building behaviour of raptors: (1) nests as an advertising signal in territories, (2) frustration nests, (3) competition avoidance by nest-site and (4) reduction of nest ectoparasites. We report here data collected during an observational study of a population of Bonelli's Eagle Hieraaetus fasciatus in southeastern Spain. Our data does not support the first two hypotheses based on the closeness of nests within territories, the lack of correlation between the number of nests and the distance to neighbours and the construction of secondary nests at similar frequencies after breeding failures as after successes. In contrast, the construction of alternative nests to avoid competition with other cliff-nesting raptor species breeding nearby was clearly important since 30% of the pairs obtained some direct benefit from the existence of alternative nests within their territories. We also found abundant Coleoptera (Dermestidae) and Diptera (Carnidae, Calliphoridae and Phoridae) as ectoparasites in nests, and the alternative use of nests, synergetically with the presence of greenery as mechanisms for avoiding ectoparasites, was an important factor for the breeding success of the eagle. Our data suggest that competition avoidance and, in particular, the reduction of nest ectoparasite hypotheses are the more plausible explanations for the maintenance of alternative nests in raptors.

Nest defence in the meadow pipit Anthus pratensis : the influence of renesting potential

Auteur(s): Václav Pavel, Stanislav Bureš
Bron: Journal of Ethology, Online article 11 January 2008
Abstract: The reproductive value hypothesis predicts that the level of nest defence is determined by the expected chance of offspring to survive until reproduction, and by the reproductive potential of the parents. Rates of survival from one breeding season to the next are low in small passerines, and their residual reproductive potential strongly declines as the current breeding season terminates. Therefore, we can expect that parents which have only one breeding attempt per season should defend their nests more intensively than parents with a possibility to renest. We studied nest defence in populations of meadow pipit (Anthus pratensis) breeding in Norway and the Czech Republic, differing in renesting potential. To simulate the threat from a predator, we placed a stuffed stoat (Mustela erminea) first 5 m and then 1 m away from a nest with nestlings. Parents increased or kept nest defence constant when the stoat approached their nests in Norway and, during a breeding season shortened by severe weather, in the Czech Republic (when renesting potential was limited). Parents decreased nest defence when the stoat approached the nest during "normal" breeding seasons in the Czech Republic (when renesting was common). These findings give support to the reproductive value hypothesis.

Secrets of bird flight revealed

Scientists believe they could be a step closer to solving the mystery of how the first birds took to the air.
A study published in the journal Nature suggests that the key to understanding the evolution of bird flight is the angle at which a bird flaps its wings.

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Green plant material versus ectoparasites in nests of Bonelli's eagle

Auteur(s): Ontiveros, D; Caro, J; Pleguezuelos, JM
Bron: JOURNAL OF ZOOLOGY 274 (1): 99-104 JAN 2008
Abstract: The greenery and arthropod nest composition has been studied in a population of Bonelli's eagle Hieraaetus fasciatus in south-east Spain, relating them to the plant availability within territories and breeding success of pairs. Greenery was invariably from trees and shrubs, with pine and oak species accounting for 78% of the nest composition in weight. All eagle pairs with Pinus pinaster availability in territories actively selected it for nest greenery. This pine species is characterized by a high level of aromatic compounds, particularly β-pinene, highly repellent for insects. The amount of pine greenery in the nest was correlated with a lower presence of ectoparasites in that nest (blow fly larvae, Protocalliphora), and higher breeding success of pairs. We discuss whether a coevolutionary process between parasites and their hosts has guided a particular nesting strategy of the eagles to improve their breeding success.

Comparative diurnal and nocturnal diet and foraging in Eurasian Golden Plovers and Northern Lapwings wintering on arable farmland

Auteur(s): Gillings, S; Sutherland, WJ
Bron: ARDEA, 95 (2): 243-257; FAL 2007
Abstract: Knowledge of diet and intake rates are useful first steps in
understanding the distribution and behaviour of foragers. The diet of
Golden Plovers and Lapwings feeding on arable farmland has been rarely
studied, yet these species increasingly occupy this habitat in winter.
They are known to feed at night but little is known about their diet
and foraging success at night. This study aimed to describe and compare
diurnal and nocturnal foraging behaviour in order to explain spatial
and temporal patterns in foraging. Over three winters
(1999/2000-2001/02) diurnal and nocturnal observations of focal
individuals and collection of faecal samples were used to reconstruct
diet and quantify intake rates across a range of arable habitats.
Numerically, arthropods (mostly Carabids and millipedes) were the main
diurnal prey types but by biomass, small earthworms were the major prey
items. Diurnal intake rates were low but comparable with other studies of these species, prompting questions concerning the profitability of
feeding on agricultural farmland and the pause-travel foraging mode.
Nocturnal intake rates were up to 50% higher due to a greater reliance
on catching large earthworms at night. Diurnal intake rates were
highest during mild weather and on grass and sugar beet stubble fields;
they were lowest on cereal crops, yet this was the habitat most
consistently occupied. Current methods for assessing earthworm
abundance limit further explanation of foraging behaviour.

Climate Change study predicts hazy future for Europe's birds

On January 15th, BirdLife International welcomed the publication of ' A Climatic Atlas of European Breeding Birds'. This Atlas marks a major advance in understanding the potential impacts of climate change on wildlife. It shows that in the course of the 21st century the changing climatic conditions will force most species to move into new areas. For many of them this will prove difficult, and combined with other threats this will increase their risk of extinction in Europe.

Lees meer: BirdLife International

Common scoter: concern over rare duck's decline

Numbers of one of the UK's rarest breeding ducks have almost halved in the past decade, a survey has revealed.
The breeding population of the common scoter is now found only in remote freshwater lochs in northern Scotland.



Lees meer: BBC News

On the song resumption, polyterritorial behaviour and their population context in the Sedge Warbler Acrocephalus schoenobaenus

Auteur(s): Zajac, T; Bielanski, W; Solarz, W
Bron: JOURNAL OF ORNITHOLOGY 149 (1): 49-57 JAN 2008
Abstract: Mating tactics in species with facultative polygyny seem to be very flexible and to depend on local environmental conditions. We analysed the habitat and population contexts of territorial behaviour, associated with polygyny, in a population of Sedge Warblers Acrocephalus schoenobaenus inhabiting natural wetlands.
Nearly one-third of all breeding males (46 individuals) resumed song after completing their mating with the first female, in order to attract another one. Resuming males were usually the earliest arrivals. There was a continuity in the territorial behaviour between resuming song on first territory and polyterritorial behaviour.
Fifty-nine percent of resuming males set up second territories, clearly separated from the first. The second territory was usually located close to the primary female activity area. The quality of the first and second territories were correlated, with second territories being significantly inferior. However, their quality was not significantly different from the territories of non-breeding males.
The quality of the second territories was also negatively related to the distance from the first territories. Polyterritorialism was influenced by population numbers: the higher the number of territorial males, the lower the number of second territories settled and the lower their average quality. Although the polygyny frequency in the studied population was very low, polyterritorial males were significantly more likely to be polygynous. We concluded that polygyny frequency can be
significantly influenced by population numbers, which might be one of the main factors responsible for the variability in the mating system in this species.

Siberian jays can communicate about behavior of birds of prey

With the aid of various alarm calls the Siberian jay bird species tells other members of its group what their main predators - hawks - are doing. The alarm calls are sufficient for Siberian jays to evince situation-specific fleeing behaviors, which enhances their chances of survival.
This discovery, being published by Uppsala University researcher Michael Griesser in the journal Current Biology, shows for the first time that animals can assess and communicate about the behavior of predators.

Lees meer: Biology News Net

Small-prey profitability: Field analysis of shorebirds' use of surface tension of water to transport prey

Auteur(s): Sora M. Estrella, José A. Masero, Alejandro Pérez-Hurtado
Bron: AUK 124 (4): 1244-1253 OCT 2007
Abstract: Previous laboratory studies have shown that Red-necked Phalarope (Phalaropus lobatus), Wilson's Phalarope (P. tricolor), Western Sandpiper (Calidris mauri), and Least Sandpiper (C. minutilla) use the surface tension of water surrounding a prey item to transport it from bill tip to mouth. Although such experimental work suggests that many species of shorebird may be capable of surface-tension feeding, no field studies have been done that examine this possibility.
We studied the occurrence and interspecific variation in the performance of surface-tension transport (STT) in wild shorebirds feeding on identical prey items in shallow water. All shorebirds videotaped - Little Stint (C. minuta), Dunlin (C. alpina), Sanderling (C. alba), Curlew Sandpiper (C. ferruginea), Common Redshank (Tringa totanus), and Black-winged Stilt (Himantopus himantopus) - used STT to feed on small prey items. Individuals employing STT used one or several cycles of jaw spreading to transport the prey contained in a drop of water upward along the bill cavity, an action indicative of STT.
Two distinct types of prey transport were observed: (1) use of STT in isolation by calidridine species following the description given in previous studies (i.e., an absence of other feeding mechanisms such as tongue movements, suction, or inertial transport), and (2) STT aided by inertial transport (head jerks) as seen in Common Redshank and Black-winged Stilt. Measured prey-transport variables (number of cycles, total time, and speed of transport) varied among species. The absence of significant relationships between these variables and measures of external morphology (bill length, bill length-to-width ratio, and bill length-to-depth ratio) suggests that some interspecific variations in STT performance may be attributable to differences in internal bill morphology. We show that STT is a common feeding mechanism in small or medium- sized shorebird species that feed on small prey items in shallow water. Birds using STT transported ≤3.6× faster than the theoretical value predicted by a previous model and can achieve high intake rates when foraging on high densities of available small prey items.

Prey size and ingestion rate in raptors: importance for sex roles and reversed sexual size dimorphism

Auteur(s): Slagsvold, Tore; A. Sonerud, Geir
Bron: JOURNAL OF AVIAN BIOLOGY, Volume 38, Number 6, November 2007
, pp. 650-661(12)
Abstract: Compared to other birds, most raptors take large prey for their size, and feeding bouts are extended. However, ingestion rate has largely been overlooked as a constraint in raptors′ foraging and breeding ecology. We measured ingestion rate by offering avian and mammalian prey to eighteen wild raptors temporarily kept in captivity, representing seven species and three orders.
Ingestion rate was higher for small than for large prey, higher for mammalian than for avian prey, higher for large than for small raptors, and higher for wide-gaped than for narrow-gaped raptors. Mammalian prey were ingested faster by raptors belonging to species with mainly mammals in their diet than by raptors with mainly birds in their diet, but the drop in ingestion rate with increasing prey size was more rapid for the former than for the latter.
We argue that the separate sex roles found in raptors, i.e. the male hunting and the female feeding the young, is a solution of the conflict between the prolonged feeding bouts at the nest, and the benefit of rapid resumption of hunting in general, and rapid return to the previous capture site in particular (the prey size hypothesis). Thus, the sex roles differ more when prey takes longer to feed, i.e. from insects to mammals to birds.
We then argue that the reversed sexual size dimorphism in raptors, i.e. smaller males than females, results from a conflict between the benefit of being small during breeding to capture the smallest items with the highest ingestion rate among these agile prey types (mammals and bird), and the benefit of being large outside the breeding season to ensure survival by being able to include large items in the diet when small items are scarce (the ingestion rate hypothesis). This hypothesis explains the observed variation in reversed sexual size dimorphism among raptors in relation to size and type of prey, i.e. increasing RSD from insects to mammals to birds as prey.