Miklós Bán

Discordancy or template-based recognition? Dissecting the cognitive basis of the rejection of foreign eggs in hosts of avian brood parasites

SUMMARY Many avian hosts have evolved antiparasite defence mechanisms, including egg rejection, to reduce the costs of brood parasitism. The two main alternative cognitive mechanisms of egg discrimination are thought to be based on the perceived discordancy of eggs in a clutch or the use of recognition templates by hosts. Our experiments reveal that the great reed warbler (Acrocephalus arundinaceus), a host of the common cuckoo (Cuculus canorus), relies on both mechanisms. In support of the discordancy mechanism, hosts rejected their own eggs (13%) and manipulated (‘parasitic’) eggs (27%) above control levels in experiments when manipulated eggs were in the majority but when clutches also included a minority of own eggs. Hosts that had the chance to observe the manipulated eggs daily just after laying did not show stronger rejection of manipulated eggs than when the eggs were manipulated at clutch completion. When clutches contained only manipulated eggs, in 33% of the nests hosts showed rejection, also supporting a mechanism of template-based egg discrimination. Rejection using a recognition template might be more advantageous because discordancy-based egg discrimination is increasingly error prone with higher rates of multiple parasitism.

Experimental support for the use of egg uniformity in parasite egg discrimination by cuckoo hosts

Common cuckoo (Cuculus canorus) parasitism drastically reduces the reproductive success of their hosts and selects for host discrimination of cuckoo eggs. In a second stage of anti-parasite adaptation, once cuckoos can lay eggs that mimic those of their hosts, a high uniformity of host egg appearance within a clutch may favour cuckoo egg discrimination. Comparative evidence provides indirect support for this hypothesis although experimental support is currently lacking. Here, we studied the effect of experimentally decreased uniformity of host egg appearance on cuckoo egg discrimination by great reed warbler (Acrocephalus arundinaceus) hosts in a population in which long-term cuckoo parasitism has led to high levels of cuckoo–host egg mimesis. We manipulated host clutch uniformity by adding extra spots to fresh host eggs just after they were laid. Rejection of non-mimetic experimental eggs added to these nests was compared with those in control nests in which uniformity was not altered. Previously, by over-painting real spots in a control group of nests, we showed a negligible effect of our paints on hosts’ perception of their eggs. We show that for the great reed warbler, non-mimetic experimental eggs were relatively more tolerated in experimental nests, i.e. with lower uniformity (40%) than in control nests (5%). This is the first experimental study, to our knowledge, which demonstrates a reduced discrimination of foreign eggs as a consequence of an increase of egg phenotypes variation perception in a cuckoo host.

Egg Eviction Imposes a Recoverable Cost of Virulence in Chicks of a Brood Parasite

Background Chicks of virulent brood parasitic birds eliminate their nestmates and avoid costly competition for foster parental care. Yet, efforts to evict nest contents by the blind and naked common cuckoo Cuculus canorus hatchling are counterintuitive as both adult parasites and large older cuckoo chicks appear to be better suited to tossing the eggs and young of the foster parents. Methodology/Principal Findings Here we show experimentally that egg tossing imposed a recoverable growth cost of mass gain in common cuckoo chicks during the nestling period in nests of great reed warbler Acrocephalus arundinaceus hosts. Growth rates of skeletal traits and morphological variables involved in the solicitation of foster parental care remained similar between evictor and non-evictor chicks throughout development. We also detected no increase in predation rates for evicting nests, suggesting that egg tossing behavior by common cuckoo hatchlings does not increase the conspicuousness of nests. Conclusion The temporary growth cost of egg eviction by common cuckoo hatchlings is the result of constraints imposed by rejecter host adults and competitive nestmates on the timing and mechanism of parasite virulence.

Internal incubation and early hatching in brood parasitic birds

The offspring of brood parasitic birds benefit from hatching earlier than host young. A proposed but little-known strategy to achieve this is ‘internal incubation’, by retaining the egg in the oviduct for an additional 24 h. To test this, we quantified the stage of embryo development at laying in four brood parasitic birds (European cuckoo, Cuculus canorus; African cuckoo, Cuculus gularis; greater honeyguide, Indicator indicator; and the cuckoo finch, Anomalospiza imberbis). For the two cuckoos and the honeyguide, all of which lay at 48 h intervals, embryos were at a relatively advanced stage at laying; but for the cuckoo finch (laying interval: 24 h) embryo stage was similar to all other passerines laying at 24 h intervals. The stage of embryo development in the two cuckoos and honeyguide was similar to that of a non-parasitic species that lay at an interval of 44–46 h, but also to the eggs of the zebra finch Taeniopygia guttata incubated artificially at body temperature immediately after laying, for a further 24 h. Comparison with the zebra finch shows that internal incubation in the two cuckoos and honeyguide advances hatching by 31 h, a figure consistent with the difference between the expected and the observed duration of incubation in the European cuckoo predicted from egg mass. Rather than being a specific adaptation to brood parasitism, internal incubation is a direct consequence of a protracted interval between ovulation (and fertilization) and laying, but because it results in early hatching may have predisposed certain species to become brood parasitic.

Naïve hosts of avian brood parasites accept foreign eggs, whereas older hosts fine-tune foreign egg discrimination during laying

BackgroundMany potential hosts of social parasites recognize and reject foreign intruders, and reduce or altogether escape the negative impacts of parasitism. The ontogenetic basis of whether and how avian hosts recognize their own and the brood parasitic eggs remains unclear. By repeatedly parasitizing the same hosts with a consistent parasitic egg type, and contrasting the responses of naïve and older breeders, we studied ontogenetic plasticity in the rejection of foreign eggs by the great reed warbler (Acrocephalus arundinaceus), a host species of the common cuckoo (Cuculus canorus).ResultsIn response to experimental parasitism before the onset of laying, first time breeding hosts showed almost no egg ejection, compared to higher rates of ejection in older breeders. Young birds continued to accept foreign eggs when they were subjected to repeated parasitism, whereas older birds showed even higher ejection rates later in the same laying cycle.ConclusionsOur results are consistent with the hypotheses that (i) naïve hosts need to see and learn the appearance of their own eggs to discriminate and reject foreign eggs, whereas (ii) experienced breeders possess a recognition template of their own eggs and reject parasitic eggs even without having to see their own eggs. However, we cannot exclude the possibility that other external cues and internal processes, accumulated simply with increasing age, may also modify age-specific patterns in egg rejection (e.g. more sightings of the cuckoo by older breeders). Future research should specifically track the potential role of learning in responses of individual hosts between first and subsequent breeding attempts by testing whether imprinting on a parasitized clutch reduces the rates of rejecting foreign eggs in subsequent parasitized clutches.

Post-ejection nest-desertion of common cuckoo hosts: a second defense mechanism or avoiding reduced reproductive success?

Hosts of the common cuckoo (Cuculus canorus), an avian brood parasite, develop antiparasite defense mechanisms to increase their reproductive success. Ejection of the parasite egg and desertion of the parasitized nest are the most typical adaptations in response to brood parasitism, but nest desertion may also occur in response to partial clutch reduction, independently from parasitism. Some great reed warblers (Acrocephalus arundinaceus) showed both mechanisms in the same incidence of cuckoo parasitism: in 18% of successful ejections of the parasite eggs, they deserted their nests. We studied if such cases of post-ejection nest-desertion are caused by brood parasitism or reduced clutch value. We experimentally parasitized clutches consisting of five or three host eggs with two painted conspecific eggs to mimic parasitic eggs, as multiple parasitism is frequent in the area. Although hosts ejected these parasitic eggs in both clutch categories (100% and 67% for the larger and smaller inital clutch sizes, respectively), we found that after manipulation, post-ejection nest-desertion frequently occurred at small (3-egg) clutches (40%), but rarely at large (5-egg) clutches (17%). The same phenomenon also occurred when unparasitized 3-egg clutches were reduced by two eggs, but not when 5-egg clutches were reduced in the same way. A logistic regression model revealed that only initial clutch size affected nest desertion of parasitized nests in our experiments. Therefore, we conclude that post-ejection nest-desertion is not a second antiparasite mechanism, which might serve as a redundant antiparasite defense, but a reaction to typically small and further decreased clutch size.

When should Common Cuckoos Cuculus canorus lay their eggs in host nests

Capsule Brood parasitic Common Cuckoo Cuculus canorus chicks hatch earlier than the nestlings of their Great Reed Warbler Acrocephalus arundinaceus hosts, but hatching priority is less consistent when Cuckoo eggs are laid after the onset of host incubation. Aim To reveal by field observations what the optimal stage is for Cuckoos to lay their eggs in relation to the host laying cycle to ensure prior hatching of the parasitic chicks. Methods We monitored the hatching of Cuckoo chicks in relation to the hosts’ laying stage at which the Cuckoo eggs appeared and also monitored host incubation behaviour. Results Great Reed Warblers incubated more on day 5 after the hosts onset of laying relative to day 3. All Cuckoo eggs hatched earlier than hosts when they were laid prior to the onset of host incubation (day 4). Cuckoo eggs also maintained hatching priority in about 2/3 of the nests when laid on days 5–6. Conclusions Most Cuckoo eggs are laid prior to the onset of host incubation and this, together with other adaptive mechanisms, ensures the prior hatching of Cuckoo eggs. Cuckoo eggs laid after the onset of incubation lose the advantage of prior hatching in approximately 30% of nests.

Simple command-line open-source software to analyse behavioural observation video recordings

Video techniques are broadly used in the field of behaviour sciences, thus there is an increasing interest in softwares that simplify the processing of recordings. One of the difficulties is that observed objects can exhibit a wide variety of behaviours that cannot usually be recognized and recorded automatically, therefore the video has to be watched and analysed manually by humans. We have developed a simple, open-source and free command-line video analysis software, that helps the processing of observation sessions from recordings and helps to verify the processed events.

Return migration of Common Cuckoos (Cuculus canorus) between breeding grounds in Hungary and wintering grounds in Africa as documented by non-PTT GPS technology

Abstract We tagged 12 adult Common Cuckoos (Cuculus canorus) with non-platform terminal transmitter (non-PTT) GPS-UHF telemetry at their breeding grounds in Hungary. One male and two female Cuckoos (one of them twice) were again observed in subsequent years, and GPS fixes documented their migration routes to and from Africa, as far south as Namibia. All four routes showed the species-typical clockwise loop migration. Although currently non-PPT GPS tracking with remotely downloadable data as an ornithological method is primarily suitable to map home ranges of birds, it could be a complement to PTT technology in migration research, especially for delivery of higher spatial accuracy.ZusammenfassungZug des Kuckucks (Cuculus canorus) zwischen den Überwinterungsgebieten in Afrika und den Brutgebieten in Ungarn, aufgezeichnet mittels nicht-Satellitenbasierter GPS-Technologie Wir markierten 12 adulte Kuckucke (Cuculus canorus) in ihren Brutgebieten in Ungarn mit nicht Satellitenbasierter GPS-UHF-Telemetrie. Ein Männchen und zwei Weibchen (eines davon zweimal) wurden in den folgenden Jahren erneut beobachtet. Die GPS-Daten zeigten ihre Zugrouten von und nach Afrika mit Namibia als südlichstem Punkt. Alle vier Routen zeigten den arttypischen Schleifenzug im Uhrzeigersinn. Obwohl in der Ornithologie derzeit nicht Satellitenbasierte GPS-UHF-Telemetrie mit Datenfernübertragung in erster Linie eingesetzt wird, um Bewegungen im Territorium aufzuzeichnen, könnte sie auch die Vogelzugforschung ergänzen, vor allem dann, wenn eine höhere räumliche Auflösung gewünscht wird.

An open framework for biodiversity databases

OpenBioMaps is a recently developed, open and free web application with distributed database background, operated by several universities and national parks. This system provides free web map services and open database access by using standard OGC protocols. One of its’ main features is that users can create new and unique database projects. The databases involved are maintained by the data providers themselves. Standard tools supplied to the users include repeatable and referable data queries, exporting, evaluations and tracking of data changes. The system also provides a programmable data service for promoting data processing.