Errors in egg-laying by female Common Cuckoo Cuculus canorus in nests of its common host

Dozens of studies have documented that brood parasites are well adapted to a brood parasitic lifestyle but not all parasitism events are successful. Co-evolution between brood parasites and their hosts is a dynamic process so it is reasonable to expect that a female brood parasite may commit errors during egg deposition by laying her eggs outside the laying period of the host, with consequent impacts on her fitness. Using an extensive dataset from a long-term study, we evaluated egg-laying patterns and errors related to the timing of egg-laying in the Common Cuckoo Cuculus canorus (hereafter ‘Cuckoo’). Specifically, we tested whether the Cuckoo avoids laying before or on the day of host clutch initiation to reduce the risk of rejection of parasitic eggs, whether laying errors will be more frequent in periods with a lack of active host nests, and whether the laying errors will be more frequent in periods with intense Cuckoo parasitism and a consequent lack of suitable host nests. We found that about one-third of Cuckoo eggs were laid on the host clutch initiation day or 1 day before, and the percentage of Cuckoo eggs laid decreased thereafter. Surprisingly, the probability of Cuckoo egg acceptance by the hosts was not affected by the egg-laying stage of the host clutch. Errors in the timing of egg-laying with fatal consequences (i.e. those precluding Cuckoo hatching because of laying in incubated or deserted clutches) were recorded in about 5% of cases. Only laying date of a Cuckoo egg had a significant effect on the probability of errors, which increased during the breeding season. This may be related to the higher number of deserted and incubated host nests at the site at the end of the breeding season. Errors in egg-laying may be attributed to young and inexperienced females but also impaired body condition or intraspecific competition may cause this behaviour. Future studies, which will test these possible explanations, will help to understand better the mechanism of co-evolutionary arms races and differences between host specialist and generalist brood parasites in various host–parasite systems.     

Mothers vigilantly guard nests after partial brood loss: a cue of nest predation risk in a paper wasp

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Post-parturial reproduction in terrestrial isopods: a partial review

This review deals with some aspects of terrestrial isopod reproduction including breeding season, breeding periods, patterns and strategies, parturition, number and size of broods and mancae. Reproductive period is described by the exact dates (i.e. season) marsupial females were collected in the field, and the duration of the breeding period. The information for both aspects was generally obtained through field work by observing marsupial females. Two reproductive patterns are used by terrestrial isopods, either a discrete (i.e. seasonal) or a continuous (i.e. non-seasonal) pattern. The discrete pattern can be either annual when females breed once a year, or they can breed biannually or multi-annually (two or more times during the year). This conclusion is based generally on observing marsupial females in the field. Therefore, this information does not apply to the reproductive pattern of the individual female since a female may use either or both patterns, i.e. seasonal and continuous. Only by raising individual females singly (with a male) can this point be clarified. This way, the breeding strategy of the same individual female can be studied. The subject is discussed and reviewed based on my research data.     

Dimethylsulphopropionate (DMSP) and proline from the surface of the brown alga Fucus vesiculosus inhibit bacterial attachment

It was demonstrated previously that polar and non-polar surface extracts of the brown alga Fucus vesiculosus collected during winter from the Kiel Bight (Germany) inhibited bacterial attachment at natural concentrations. The present study describes the bioassay-guided identification of the active metabolites from the polar fraction. Chromatographic separation on a size-exclusion liquid chromatography column and bioassays identified an active fraction that was further investigated using nuclear magnetic resonance spectroscopy and mass spectrometry. This fraction contained the metabolites dimethylsulphopropionate (DMSP), proline and alanine. DMSP and proline caused the anti-attachment activity. The metabolites were further quantified on the algal surface together with its associated boundary layer. DMSP and proline were detected in the range 0.12–1.08 ng cm^?2 and 0.09–0.59 ng cm^?2, respectively. These metabolites were tested in the concentration range from 0.1 to 1000 ng cm^?2 against the attachment of five bacterial strains isolated from algae and sediment co-occurring with F. vesiculosus. The surface concentrations for 50% inhibition of attachment of these strains were always <0.38 ng cm^?2 for DMSP and in four cases <0.1 ng cm^?2 for proline, while one strain required 1.66 ng cm^?2 of proline for 50% inhibition. Two further bacterial strains that had been directly isolated from F. vesiculosus were also tested, but proved to be the least sensitive. This study shows that DMSP and proline have an ecologically relevant role as surface inhibitors against bacterial attachment on F. vesiculosus.     

Distribution of duck broods relative to habitat characteristics in the Prairie Pothole Region

Conservation programs for breeding ducks in the Prairie Pothole Region (PPR) of the United States and Canada require effective means of evaluating and characterizing breeding habitat across large landscapes. Extensive surveys of the distribution of duck broods in late-summer could help identify wetland basins with greater probabilities of occupancy. Broods are difficult to detect, however, rendering presence–absence data from single-visit surveys difficult to interpret, particularly when probability of detection is related to habitat features. Multiple-visit occupancy surveys offer a potential solution. From 20 July to 5 August 2007–2009, we conducted a 3-visit survey of wetland basins located on 167 10.4-km² study plots in the PPR. Our survey focused on broods of the 5 most common breeding duck species (Anas spp.). Our main objectives were to investigate ecological relationships between occupancy of wetland basins by broods and habitat characteristics and to examine if habitat-specific detection was of enough concern to warrant multi-survey approaches in the future. We surveyed 3,226 wetland basins during the study. Probability of occupancy of a wetland basin by a brood was positively related to the log of wet area for all 5 study species and was greater on wetlands located on plots with a greater proportion of herbaceous perennial cover for 4 of 5 species. For example, the median probability of occupancy for gadwall (Anas strepera) increased from 0.08 (90% Credible Interval [CrI]: 0.07, 0.10) to 0.28 (90% CrI: 0.23, 0.33) as wet area increased from 0.19 ha to 2.12 ha, and increased from 0.12 (90% CrI: 0.09, 0.16) to 0.20 (90% CrI: 0.16, 0.25) as proportion of perennial grass cover on the study plot increased from 0.03 to 0.99. Because occupancy and detection were both related to attributes of wetland basins, we concluded that the multiple-visit survey was a useful approach for identifying habitat relationships of duck broods. Our results indicated that most broods of the study species were found in 10.4-km² landscapes with greater densities of small- to mid-sized wetland basins and a greater proportion of herbaceous perennial vegetation. Our study provided new empirical support that could be used to help target conservation actions to the most productive landscapes for breeding ducks. © 2012 The Wildlife Society.     

Habitat complexity affects how young of the year Atlantic cod Gadus morhua perceive predation threat from older conspecifics

The response of age 0+ year juvenile Atlantic cod Gadus morhua to the presence of age 1+ and age 3+ year conspecifics was measured with and without cover available. Juveniles reacted by aggregating more closely and maintaining distance from older conspecifics in an experimental setting without cover but only to age 3+ year conspecifics when cover was available. The results indicate that prior residence of older juveniles can affect age 0+ year juveniles during benthic settlement and highlights the conservation value of structurally complex nursery habitats.     

Do sex ratio and development differ in sexually size‐dimorphic shiny cowbirds (Molothrus bonariensis) parasitizing smaller and larger hosts?

Two possible patterns of bias in primary sex ratio have been proposed for size‐dimorphic brood parasites that do not evict host chicks: (1) larger males should be laid at greater frequency in hosts larger than the parasite because they compete better (increasing their survival) than females with large host nest‐mates, and (2) more costly males (i.e. the larger sex) should be laid at greater frequency in hosts smaller than the parasite because, in these hosts, parasite nestlings are provisioned at a higher rate and grow faster than in larger hosts. We tested these hypotheses in two hosts of the sexually size‐dimorphic shiny cowbird, Molothrus bonariensis, one smaller (house wren, Troglodytes aedon) and one larger (chalk‐browed mockingbird, Mimus saturninus) than the parasite. We measured: (1) sex ratio at laying; (2) development of sexual differences in body mass during the nestling stage; and (3) chick survival and sex ratio of chicks before fledging. In both hosts, we found sexual differences in body mass of nestlings from 7 days of age onwards, although we did not find a bias in the sex ratio of eggs laid and chicks fledged. The results of the present study do not support the hypothesis that shiny cowbird females benefit from biasing the primary sex ratio depending on the size of the hosts they parasitize. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 442–448.     

Bird attacks on a butterfly with marginal eyespots and the role of prey concealment against the background

Small eyespots on butterflies have long been thought to deflect attacks, and birds are the presumptive drivers selecting for these patterns; however, evidence of this function is still ambiguous. Marginal eyespots typically consist of a UV‐reflective white pupil, surrounded by one black and one yellowish ring. We have recently shown that Cyanistes caeruleus (blue tits) attack such eyespots, but only under low light intensities with accentuated UV levels: the increased salience of the eyespots relative to the rest of the butterfly probably explains this result. Possibly the background against which the butterfly is concealed may deceive birds to make similar errors. We therefore presented speckled wood butterflies decorated with eyespots (or controls without eyespots) to C. caeruleus against two backgrounds: oak and birch bark. Our results show that: (1) eyespots, independent of background, were effective in deflecting attacks; (2) the time elapsed between a bird landing and the attack was interactively dependent on the background and whether the butterfly bore an eyespot; and (3) the speed at which a butterfly was attacked predicted the outcome, with faster birds being more prone to errors than slower birds. This underscores a speed–accuracy trade‐off in the predators, and that background plays a role in the defensive qualities of marginal eyespots. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 290–297.     

Parental differences in brood provisioning by Hen Harriers Circus cyaneus

Capsule Females varied their provisioning patterns according to brood age and brood size, whereas males did not.

Aims To quantify how parents balance the needs of their offspring for food and protection.

Methods We studied 13 nests from hides and spent on average 101 hours per nest monitoring prey types, provisioning rate and the time spent at the nest by both sexes in relation to brood size and brood age.

Results Males always provided more food than females. Males brought similar amounts of prey items irrespective of brood size and nestling age, whereas females brought more prey and bigger items to larger and older broods. Females spent less time brooding larger broods, particularly early on.

Conclusions Hen Harrier parents share the provisioning burden, with each parent delivering prey as a function of brood care requirements, hunting capability and the behaviour of the other parent.