Bill morphology and biometrics of three sibling woodpecker species from sympatric populations

ABSTRACT

Capsule Different methods of comparing bill morphology between woodpecker species show different, but not contradictory results.

Aims Differences among similar, closely related species which co-occur are still highly debated. In such a scenario, species should diverge morphologically to reduce competition. We studied this phenomenon, in three closely related woodpecker species that co-occur in eastern Slovakia: Great Spotted Woodpecker Dendrocopos major, Syrian Woodpecker Dendrocopos syriacus and White-backed Woodpecker Dendrocopos leucotos. The Great Spotted Woodpecker has the widest niche and lives sympatrically with both Syrian and White-backed Woodpeckers, while the distributions of the latter two species do not overlap because of their use of different habitats. We predicted that Great Spotted Woodpeckers should differ morphologically from both sympatric species: Syrian and White-backed Woodpeckers.

Methods Comparisons were made between species, based on dorsal and lateral views of maxilla using both geometric morphometric techniques and traditional measurements.

Results We confirmed our hypothesis, and found significant differences in bill shape between Great Spotted Woodpecker and both congeners. This is in contrast to the observed higher similarity of Great Spotted Woodpecker and Syrian Woodpecker in traditional body measurements. However, surprisingly, Syrian Woodpecker and White-backed Woodpecker do not differ significantly in bill shape.

Conclusions This work indicates that geometric morphometry appears to be a promising tool for the investigation of how interspecific competition influences the shape of the bill between co-occurring species.     

Bemerkungen zum Maurenspecht,Picoides major numidus

Zusammenfassung Voous (1947) meinte, der BlutspechtPicoides syriacus und eine gut gekennzeichnete nordafrikanische Unterart des BuntspechtsP. m. numidus seien die Nachfahren von Rückzugs-populationen des Buntspechtes während der Mindel-Eiszeit. Alle morphologischen Merkmale, die sonst zur Unterscheidung von Blut- und Buntspecht herangezogen werden, zeigen, daßP. m. numidus ein Buntspecht ist. Dasselbe trifft für die Lautäußerungen zu. Im Gegensatz zu europäischen Rassen weistP. m. numidus einen ökologischen Sexualdimorphismus auf. gehen öfter in der Kronenschicht der Nahrungssuche nach. Sie halten sich dabei auch öfter an dünnen Zweigen auf als . Kein deutlicher Unterschied besteht bezüglich der Tätigkeiten des Nahrungserwerbs. Ökologisch ist die nordafrikanische Rasse mitteleuropäischen Buntspechten ähnlicher als Blutspechten. In der Erörterung des ökologischen Sexualdimorphismus wird auf das inselartige Vorkommen, die Eintönigkeit des Lebensraumes, das offensichtliche Fehlen einer Nahrungsspezialisierung im Winter, Merkmalsfreisetzung und die Rolle der Geschlechter im Fortpflanzungsgeschehen eingegangen. Die Auffassung wird vertreten, daßP. m. numidus keine unmittelbaren historischen Beziehungen zuP. syriacus hat.

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Remarks onPicoides major numidus

Summary Voous (1947) proposed that the Syrian WoodpeckerPicoides syriacus and an distinct North African subspecies of the Great Spotted WoodpeckerPicoides major numidus are the descendants of refugial populations of the Great Spotted Woodpecker during the Mindel glaciation. All morphological characters commonly used for discerningP. major andP. syriacus show thatP. m. numidus belongs to the former species. The same is true for the vocalizations. In contrast to European subspeciesP. m. numidus exhibits an ecological sexual dimorphism. Females feed more often in the crown of a tree. They also forage more often on thin twigs than males do. No significant difference between the feeding techniques of male and female was found. The North African subspecies is more similar ecologically to Central European Great Spotted Woodpeckers than to Syrian Woodpeckers. In discussing the ecological sexual dimorphism the insular distribution, the low habitat diversity, the apparent lack of a specialized winter food, competitive release and the role of the sexes in the breeding cycle are considered. It is pointed out that this situation does not allow to explain the dimorphism by the sole action of one of these factors. It is suggested thatP. m. numidus has no direct historical relationship withP. syriacus.

     

Characteristics of woods used recently and historically by Lesser Spotted Woodpeckers Dendrocopos minor in England

Lesser Spotted Woodpecker Dendrocopos minor numbers have declined greatly in England since the early 1980s for reasons that are not yet fully understood. It has been suggested that the species’ decline may be linked to the increase in Great Spotted Woodpeckers Dendrocopos major, changes in woodland habitat quality (such as deadwood abundance) and landscape‐scale changes in tree abundance. We tested some of these hypotheses by comparing the characteristics of woods in southern England where the species is still relatively numerous with those of woods used in the 1980s before the major decline. In each time period, habitat, predator and landscape information from woods known to be occupied by Lesser Spotted Woodpeckers was compared with those found to be unoccupied during surveys. Before the main period of decline, Lesser Spotted Woodpeckers used oak‐dominated, mature, open woods with a large amount of standing deadwood. Habitat use assessed from recent data was very similar, the species being present in mature, open, oak‐dominated woodlands. There was a strong relationship between wood use probability and the extent of woodland within a 3‐km radius, suggesting selection for more heavily wooded landscapes. In recent surveys, there was no difference in deadwood abundance or potential predator densities between occupied and unoccupied woods. Habitat management should focus on creating and maintaining networks of connected woodlands in areas of mature, open woods. Finer‐scale habitat selection by Lesser Spotted Woodpecker within woodlands should be assessed to aid development of beneficial management actions.     

The utilization of dead wood resources by woodpeckers in Britain

Dead wood is important for woodpeckers, providing foraging, roost and nest-sites. In this paper, data from long-term studies of woodpeckers and dead wood in oakwoods in southern England are used to examine the dead wood requirements of the three British resident woodpecker species. Both Great Dendrocopos major and Lesser Spotted Woodpeckers Dendrocopos minor select dead trees for nest-sites although the former is able to nest in living trees too. On the other hand a smaller fraction of Lesser Spotted Woodpecker nests are in living trees. Green Woodpecker Picus viridis shows no selection for dead nesting trees. Hence the smallest woodpecker species appears to be most dependent on dead and decaying trees for nest-sites. Great and Lesser Spotted Woodpeckers show no preference for foraging on dead trees although they both make use of dead branches on living trees. Lesser Spotted Woodpeckers forage on smaller branches higher in the tree than Great Spotted Woodpeckers. There has been a trend for increasing dead wood resources in the study woods with both dead wood on the ground and standing dead trees (snags) increasing in the last 20 years. The levels of dead wood are shown to be the result of continual processes of creation and decay. Around 0.5% of oak Quercus spp., Ash Fraxinus excelsior and Hornbeam Carpinus betulus and 3.4% of the birch Betula spp. trees die each year in the woods resulting in a continuity of new dead snags and fallen trees. There is a high turnover of standing dead snags of oak and birch with 95% and 80% annual survival, respectively. Snags are only suitable for nesting Great Spotted Woodpeckers for a few years after their creation. It is suggested that these stand and dead wood dynamics are likely to provide habitats more favourable for the Great Spotted than the Lesser Spotted Woodpecker.     

Reproductive success and nestling diet in the Lesser Spotted Woodpecker ( Picoides minor ): the early bird gets the caterpillar

Populations of Lesser Spotted Woodpecker (Picoides minor) are decreasing in size, necessitating management strategies. However, data on the reproductive biology of this species are scarce. The aim of this study was to investigate the influence of timing of breeding and nestling diet on the reproductive success of the Lesser Spotted Woodpecker and thereby contribute to an understanding of the determinants influencing its reproductive success. During 6 study years between 1996–2003, we investigated various variables of reproductive success in a Lesser Spotted Woodpecker population in the Taunus low mountain range, Germany. We observed nestling feeding at breeding holes to assess the composition of nestling diet and how it changes during the season. Clutch size, number of fledglings as well as body mass of the nestlings declined with the start of egg laying. Pairs composed of individuals that had breed together in previous years started egg laying earlier than newly established pairs. Nestling diet consisted mainly of aphids, caterpillars, craneflies and wood-living larvae. The composition changed considerably within the breeding season in both early and late broods. However, early broods were provided with caterpillars more frequently, whereas late broods received wood-dwelling larvae more often. Our results suggest that Lesser Spotted Woodpeckers time their breeding so as to coincide with the early nestling stage with the highest availability of caterpillars, since this is the time of highest energy demand. Moreover, food availability declines during the breeding season, and the decline in reproductive performance seems to be an effect of this development.     

Drivers of low breeding success in the Lesser Spotted Woodpecker Dendrocopos minor in England: testing hypotheses for the decline

Capsule The breeding success of Lesser Spotted Woodpeckers Dendrocopos minor is now lower in England than previously reported and also lower than found in studies elsewhere in Europe.

Aims To quantify the breeding success and identify the causes of nest failure. To test the hypotheses that breeding success is related to aspects of food limitation and parental care, and inclement weather during the nesting period, or to interactions with Great Spotted Woodpeckers.

Methods Nests were monitored in three regions of England, recording survival and causes of failure. We measured aspects of food limitation and parental care, rainfall and Great Spotted Woodpecker interactions at nests, to explore whether there was any evidence that these factors were related to breeding success. We compared results to other studies from the UK and continental Europe.

Results Nest survival was 52%. The average number of chicks produced from successful nests was 2.8. Chick-stage daily nest survival was positively related to provisioning rates, indicating that food supply may be limiting. The most common cause of nest failure was presumed starvation of chicks after the disappearance of an adult. Some females ceased visiting nests, leaving provisioning solely to the male. This behaviour has been reported elsewhere in Europe, but in the present study males were unable to compensate fully by increasing their provisioning rates, leading to poor nest survival. Provisioning rates and chick-stage daily nest survival were negatively associated with rainfall. Nest predation by Great Spotted Woodpeckers occurred but was a less frequent cause of failure. Aggressive interactions were recorded between the two woodpecker species but these were unrelated to breeding parameters.

Conclusions Low breeding success is most probably related to food shortages in the breeding period. Simple population modelling using parameters from the present study and from published work shows that if the low productivity that we have observed is replicated throughout Britain, it would be sufficient to account for the observed population decline. However, the possibility that survival rates are also low cannot be ruled out.     

Beobachtungen zum Bearbeiten von L?rchenzapfen (Larix decidua) in einer Schmiede des Buntspechts (Dendrocopos major)

Zusammenfassung Ein Buntspecht(Dendrocopos major) wurde beim Bearbeiten von Lärchenzapfen(Larix decidua) beobachtet; verschiedene Verhaltensweisen wurden gemessen. Die Bearbeitungsdauer ist bei trockener Witterung länger als bei nasser (Abb. 2). Während des Bearbeitens wird der Zapfen in regelmäßigen Zeitabständen gedreht (Abb. 3 unten); das heißt, daß mit zunehmender Bearbeitungsdauer die Häufigkeit des Drehens linear anwächst (Abb. 4). Für das Heranholen eines neuen Zapfens benötigt der Specht durchschnittlich 43 sec. Die Daten werden mit solchen vom Fichtenkreuzschnabel(Loxia curvirostra) verglichen.

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Observations on the Great Spotted Woodpecker(Dendrocopos major) when working on larch cones(Larix decidua) in a cleft

Summary Different activities of a Great Spotted Woodpecker working on larch cones forced into a cleft (Spechtschmiede) were measured. Dry cones are worked on longer than wet ones (Fig. 2). During the work the Woodpecker turns the cone at regular intervals of time (Fig. 3, below); i. e. the frequency of turning grows in a linear manner with increasing duration of the work on one cone (Fig. 4). To take a fresh cone, the Woodpecker takes generally 43 seconds. The results are compared with those obtained with the common crossbill(Loxia curvirostra).

     

Der embryonale Sauerstoffverbrauch des Buntspechts (Dendrocopos major): Einflu? von Entwicklungsmodus und Bebrütungszeit

Zusammenfassung Der Sauerstoffverbauch von zwei Eiern des Buntspechtes (Dendrocopos major) wurde während der letzten sechs Tage der Embryogenese mit Hilfe eines Durchflußrespirometers gemessen. Der zeitliche Verlauf des embryonalen Stoffwechsels folgt annähernd einer Exponentialfunktion mit Ausnahme einer siebenstündigen Plateauphase am 9. Bebrütungstag. Während der gesamten Embryogenese setzt der Buntspecht 0.9 kJ × g^–1 Frischeimasse um. Dies entspricht nur etwa dem halben Umsatz durchschnittlicher Vogelembryonen (rund 2 kJ × g^–1). Als Ursache dafür wird die kurze Bebrütungszeit des Buntspechts (10 Tage) diskutiert.

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Embryonic oxygen consumption in the Great Spotted Woodpecker (Dendrocopos major) — influence of developmental mode and incubation period

Oxygen consumption of two eggs of the Great Spotted Woodpecker was measured with a two-channel oxygen analyzer using an open flow system. The embryogeny of oxygen consumption nearly follows an exponential equation with the exception of a 7-hour plateau phase on day 9 of incubation. During this period the embryos consume ca. 4 ml O₂ × min^–1. For a given fresh egg mass the eggs of woodpeckers have unusually short incubation periods (10 days measured vs. 17 days expected). Thus a comparison of the embryonic metabolism with that of species having long incubation periods but similar egg sizes shows the influence of a fast embryonic development on avian enbryonic energetics. The total embryonic metabolism of the Great Spotted Woodpecker amounts to 0.9 kJx g^–1 fresh egg mass which is half as much as the value for most other birds (ca. 2 kJ × g^–1).

     

Attributes of trees used by nesting and foraging woodpeckers (Aves: Picidae) in an area with old pollarded Oaks (Quercus spp.) in the Taurus Mountains,Turkey

We used three woodpecker species as umbrella species for old deciduous forests, and analysed their preferences in an area with old pollarded oaks in the Taurus Mountains, Turkey. Using plot inventories, we physically characterised trees utilised for nesting and foraging amongst woodpeckers in general and the Middle Spotted Woodpecker (Leiopicus medius) in particular. Trees more frequently visited by foraging woodpeckers differed from randomly chosen trees by being taller, having a larger circumference, greater bark furrow depth and shorter distance to neighbouring trees. Nesting trees were taller, had a higher proportion of dead wood but a lower surface area of natural cavities. Our results suggest that the woodpeckers in the study area rely upon woodlands containing mature trees, thus have the potential to function as suitable umbrella species’ to highlight the conservation value of oak forest habitats in southern Turkey.     

农田林网条件下大斑啄木鸟夏季和冬季日间行为模式

2005年7月至2008年1月,利用目标动物取样法对内蒙古乌拉特前旗地区农田林网中大斑啄木鸟(Picoides major)夏季和冬季的日间行为模式进行了分析.结果发现,大斑啄木鸟不同行为的活动次数差异极为显著,主要活动是觅食啄食;夏季具午间休息习性,日间行为节律明显,而冬季没有午休习性,日问行为节律不明显;不同性别大斑啄木鸟之间的日间行为差异不显著,但大斑啄木鸟在不同季节的日间行为差异极为显著,夏季活动时间明显长于冬季.     

The carotenoid‐based red cap of the Middle Spotted Woodpecker Dendrocopos medius reflects individual quality and territory size

Carotenoid‐based plumage ornaments have the potential to signal individual condition and health in many species of birds. However, very little is known about the function of red plumage in woodpeckers. We assessed whether the red cap displayed by both male and female Middle Spotted Woodpeckers reflects individual quality, finding that the size of the cap is sex‐dependent, whereas the brightness of the cap correlates with the body condition of an individual. Furthermore, birds with brighter caps had larger clutches, suggesting that cap coloration may be an honest signal of parental quality in woodpeckers. Interestingly, more colourful individuals also occupied smaller territories, suggesting that territory size and territory quality may be inversely related in the Middle Spotted Woodpecker.     

Mixed species flocking of tits (Parus spp.): a field experiment

Summary We tested two general models of flocking behaviour, namely the antipredation model and foraging efficiency model on mixed-species tit flocks (Parus spp.). After food addition the size of mixed-species flocks was significantly less than in the control samples. In the presence of extra food significantly more birds were observed either in monospecific flocks or solitary, than during the control observations. In the presence of a living predator the birds foraged in larger mixed-specifies flocks than during the control observations. In addition, the social behaviour of Great Spotted Woodpecker, Middle Spotted Woodpecker and Nuthatch shifted to mixed-specific flocking. The size of monospecific flocks was independent of both treatments. The density of birds increased significantly after food addition, while in the predator presence the birds tended to leave the forest. These results support the view that both the antipredation model and foraging efficiency model seem to be valid for mixed-species flocking. However, in the case of monospecific flocks, the territory maintenance could be the most important factor.     

Effects of the winter beechmast crop on bird occurrence in British gardens

Capsule Woodland birds were significantly less likely to occur in gardens in years of high beechmast crop.

Aim To test the hypothesis that woodland species that feed on beechmast will have significantly lower occurrence rates at garden feeders in mast years.

Methods Weekly winter occurrence rates at garden feeders between 1970/71 and 1999/2000 for 40 species were analysed in relation to annual beechmast abundance, classified into low, medium and high years. A repeated-measures logistic regression model was used to assess whether beechmast abundance explained further significant variation additional to underlying seasonal and annual trends.

Results Seven species that commonly feed on beechmast showed significantly lower occurrence in gardens in years of highest beechmast abundance: Great Spotted Woodpecker Dendrocopos major, Woodpigeon Columba palumbus, Great Tit Parus major, Coal Tit Periparus ater, Nuthatch Sitta europaea, Jay Garrulus glandarius and Chaffinch Fringilla coelebs. Blackbird Turdus merula and Siskin Carduelis spinus, which showed similar significant patterns, are likely to take beechmast as elements of their diet. Pied Wagtail Motacilla alba was the only insectivorous species to show significant effects, but occurrence was lowest in years of intermediate beechmast abundance. For the latter species, this may have been due to confounding effects of temperature, but there were no such confounding effects of either temperature, or the number of bird feeders provided in gardens, for the other nine species.

Conclusion Use of artificial food sources by birds in gardens is influenced by resources in the surrounding countryside, suggesting that food provided in gardens may play a significant part in the population dynamics of these species, that population monitoring without consideration of the garden habitat may be deficient, and that volunteer-based garden bird recording may provide data that can be used as an indicator of changes in the wider countryside.     

Habitatansprüche des Kleinspechts(Dendrocopos minor) in W?ldern der Nordost-Schweiz

Zusammenfassung Viele Aspekte der Autökologie des Kleinspechts(Dendrocopos minor) sind schlecht untersucht. Dies gilt in besonderem Maß für seine Habitatansprüche in den Wäldern Mitteleuropas. Ein Ziel der vorliegenden Arbeit bestand deshalb darin, in ausgewählten Wäldern der Nordost-Schweiz die für den Kleinspecht relevanten Habitatstrukturen zu identifizieren. Ausserdem wurde die Eignung von Tonband-Klangattrappen für die Kartierung untersucht. Für die Habitatanalyse wurden in 21 der 22 Wälder mit Kleinspechten und in einer Kontrollgruppe von 21 Wäldern ohne Kleinspechtvorkommen verschiedene Habitatvariablen erhoben. Mit einer logistischen Regression wurden die Variablen ermittelt, die am meisten zur Unterscheidung der beiden Gruppen beitragen. Es resultierten vier Variablen als Prädiktoren für das Vorkommen von Kleinspechten: 1) Weichhölzer begünstigen die Anwesenheit des Kleinspechts; 2) besiedelte Wälder weisen eine geringere Entfernung zu einem Gewässer auf; 3) Kleinspechte kommen hauptsächlich in tieferen Lagen vor; 4) Die untersuchten Kleinspecht-Wälder weisen im Vergleich mit den Kontrollwäldern weniger stehende tote Bäume mit BHD 15 cm auf. Die Erhebung von Kleinspecht-Beständen mit einer Klangattrappe kann während eines kurzen Zeitraums im März/April effizient und zuverlässig durchgeführt werden.

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Habitat requirements of the Lesser Spotted Woodpecker(Dendrocopos minor) in forests of northeastern Switzerland

Summary Despite the widespread distribution of the Lesser Spotted Woodpecker, many aspects of the species' biology are poorly known, particularly regarding its habitat requirements in central European forests. Recent studies suggest population declines in many areas of its range, making the need for appropriate management guidelines urgent. In 1997, we examined which habitat factors affect the presence of the Lesser Spotted Woodpecker in decidous lowland, non-riverine forests of northeastern Switzerland and evaluated the usefulness of playback tapes for censusing the species. Selected on the basis of prior knowledge of the species' distribution, 27 forests were searched for Lesser Spotted Woodpeckers using playbacks from March to early May. The species was still present in 17 of these formerly occupied forests, while 5 new registrations were made in previously unoccupied forests. Ninety percent of the registrations occurred between 16 March and 24 April, and the woodpeckers responded to the playbacks most often with call series. The habitat structure of forests with Lesser Spotted Woodpeckers was compared with that of forests where the species had been absent both during previous censuses and in 1997, and which had a similar tree species composition, forest structure and elevation to the occupied forests. Logistic regression analysis identified four habitat variables as significant predictors of the species' presence/absence. Accordingly, forests were most likely occupied by the Lesser Spotted Woodpecker if more softwoods, but fewer snags (with a DBH 15 cm) per area were available, if the distance to lakes and rivers was small, and the elevation was low. Therefore, the distribution of the Lesser Spotted Woodpecker seems to be affected by variables reflecting both forest structure and relative position of the forests within the landscape. We conclude that the Lesser Spotted Woodpecker will benefit from protection and promotion of softwood in all forest types, resulting in increased habitat connectivity. Moreover, censuses using playbacks can be efficiently conducted during a short period in March/April.

     

笼养大斑啄木鸟行为时间分配和活动节律

2011年6～8月,在北京市野生动物救护中心露天笼舍内,采用瞬时扫描法对笼养条件下的4只大斑啄木鸟(Dendrocopos major)行为时间分配和活动节律进行了研究,利用单因素方差分析来说明不同性别大斑啄木鸟间行为时间分配差异以及研究对象在日间不同时间段行为节律差异.结果显示,笼养条件下大斑啄木鸟的各种行为活动具有一定的时间分配特点和日行为节律.大斑啄木鸟的行为主要表现为休息和飞行走动,占全部行为的36.24％和26.96％,其次为觅食行为,占17.69％.除觅食、理羽和其他行为外,雌雄间行为时间分配差异不显著(P＞0.05).大斑啄木鸟昼间活动的高峰期出现在上午,中午有午休现象,日间行为节律明显.飞行走动、休息、理羽、跳跃行为的发生频次在雌雄间无显著差异(P＞0.05),而雄性觅食的发生频次显著地大于雌性的(P＜0.05).     

Do Oaks Quercus spp., dead wood and fruiting Common Ivy Hedera helix affect habitat selection of the Middle Spotted Woodpecker Dendrocopos medius?

Capsule The occurrence of the Middle Spotted Woodpecker in northern Switzerland was related to the availability of large oaks and standing dead trees, but not to trees with fruiting Common Ivy.     

Morphometrics confirm taxonomic deflation in dwarf lemurs (Primates: Cheirogaleidae), as suggested by genetics

Detailed knowledge of the identity and distributions of extant species is essential for unravelling patterns and mechanisms of biodiversity, and it provides indispensable baseline data for conservation efforts. The taxonomy of the primates of Madagascar (Lemuriformes) has experienced drastic revisions in the last decades, with species numbers skyrocketing, especially in the genera Microcebus, Avahi, and Lepilemur. The dwarf lemurs (genus Cheirogaleus) have received less attention in terms of their taxonomy, even though they are closely related and syntopic with these diverse genera. The last revision of the genus was based on morphological data from museum specimens, and accepted seven species: Cheirogaleus medius, Cheirogaleus major, Cheirogaleus crossleyi, Cheirogaleus adipicaudatus, Cheirogaleus sibreei, Cheirogaleus ravus, and Cheirogaleus minusculus, whereas a more recent multilocus molecular study only detected three lineages: C. medius, C. major, and C. crossleyi. The goal of this study was to reassess the currently accepted taxonomy of the genus by examining six external and 32 craniodental characters of 120 museum specimens and 36 new specimens from the field. This study, in conjunction with a complementary molecular study, revealed lower diversity and a lower number of distinct morphs of dwarf lemurs than previously postulated. We conclude that in our sample there are three distinct morphs in the genus Cheirogaleus that correspond to C. medius, C. major, and C. crossleyi. We formally recognize C. adipicaudatus and C. ravus as synonyms of C. medius and C. major, respectively, and consider C. minusculus and C. sibreei to be potential synonyms of C. medius. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010.     

Compensation for predator-induced reduction in nestling feeding rate in the Great Spotted Woodpecker

Parent birds make efforts to prevent the immediate costs of predation through plastic behavioural responses to the actual predation risk, but this may incur future costs for offspring due to reduced parental care. However, the temporary nature of predator encounters suggests that nestling feeding reduced during the risky periods may be later compensated for by an increased feeding effort (the predation risk allocation hypothesis). We tested this prediction in the Great Spotted Woodpecker (Dendrocopos major) confronted with its major nest predator/competitor, the European Starling (Sturnus vulgaris). A brief encounter with a live starling was followed by a reduction in the nestling feeding rate, but the lost feedings were subsequently compensated for by an increased feeding rate. This compensatory effect was higher in older nestlings that are highly demanding in terms of energy requirements and fitness value from the parents’ perspective. Thus, birds are potentially able to respond not only to the immediate risk of nest predation by nest defence but also to compensate for the potential costs of nest defence in terms of unfulfilled nestling demands. However, data on the amount of delivered food are necessary to distinguish whether parents truly compensate for lost feeding or whether the increased feeding frequency represents a nest guarding strategy.     

The advantages of social foraging in downy woodpeckers

I investigated the advantages gained by downy woodpeckers (Picoides pubescens) which join mixed-species winter flocks. Woodpeckers foraging alone showed high levels of vigilance as measured by head-cocking rates, and low feeding rates. Woodpeckers foraging with one or two flock members showed intermediate rates of head-cocking and feeding, while woodpeckers foraging with flocks of three or more birds showed low head-cocking rates and high feeding rates. Although local enhancement and copying may contribute to the woodpeckers' increased foraging efficiency in a flock, these do not appear to be the main factors. As downy woodpeckers spend less time on vigilance, they devote more time to foraging, thereby increasing their foraging efficiency     

The effect of social dominance on foraging by the Three-toed Woodpecker Picoides tridactylus

During the winter, female Three-toed Woodpeckers Picoides tridactylus , when unaccompanied by the male, foraged at a lower height above the ground and on tree trunks of greater diameter than when foraging together with a male. Among males, however, no such differences were found between those birds foraging in the absence of, or in company with, a female. The niche breadth of the males was less than that of the females, indicating a higher degree of specialization by the males. The niche overlap between the sexes was less when the birds foraged together in pairs, especially as regards foraging height and foraging site diameter. The intersexual segregation of foraging niche recorded for the Three-toed Woodpecker is therefore probably not determined genetically, but is due to social dominance by males which obliges the females to occupy the less preferred niche. Both sexes spent less time being vigilant when foraging together, than when alone.