Ancient origin and maternal inheritance of blue cuckoo eggs

Maternal inheritance via the female-specific W chromosome was long ago proposed as a potential solution to the evolutionary enigma of co-existing host-specific races (or 'gentes') in avian brood parasites. Here we report the first unambiguous evidence for maternal inheritance of egg colouration in the brood-parasitic common cuckoo Cuculus canorus. Females laying blue eggs belong to an ancient (∼2.6 Myr) maternal lineage, as evidenced by both mitochondrial and W-linked DNA, but are indistinguishable at nuclear DNA from other common cuckoos. Hence, cuckoo host races with blue eggs are distinguished only by maternally inherited components of the genome, which maintain host-specific adaptation despite interbreeding among males and females reared by different hosts. A mitochondrial phylogeny suggests that blue eggs originated in Asia and then expanded westwards as female cuckoos laying blue eggs interbred with the existing European population, introducing an adaptive trait that expanded the range of potential hosts

Within-year nest reuse in open-nesting, solitary breeding passerines

During fieldwork at Lake Sic (46°57’N, 23°54’E), Romania, in the summer of 2003, we observed a strange incident of nest reuse in the Great Reed Warbler Acrocephalus arundinaceus. After first laying a complete clutch of five eggs and then ejecting an experimentally added parasite egg together with two of its own eggs, a new clutch was initiated in the same nest. In Tana (70°16’N, 28°19’E), Norway, in June 2003, we observed a similar incident in the Brambling Fringilla montifringilla. In a nest that was completely depredated when 3-4 eggs had been laid, a new clutch was initiated 8-9 days later. This is as far as we know the first time nest reuse has been documented in Great Reed Warblers and Bramblings

Sex Allocation in Relation to Host Races in the Brood-Parasitic Common Cuckoo (Cuculus canorus)

Sex allocation theory and empirical evidence both suggest that natural selection should favour maternal control of offspring sex ratio in relation to their ability to invest in the offspring. Generalist parasites constitute a particularly interesting group to test this theory as different females commonly utilize different host species showing large variation in provisioning ability. The common cuckoo (Cuculus canorus) is a generalist brood parasite that lays its eggs in the nest of many different passerine birds, but each female tends to specialize on one particular host species giving rise to highly specialized host races. The different host species show large variation in their ability to invest in the parasitic offspring, presenting an opportunity for female cuckoos to bias offspring sex ratio in relation to host species quality. Here, we investigate host-race specific sex allocation controlling for maternal identity in the common cuckoo. We found no evidence of any significant relationship between host race and sex ratio in one sympatric population harbouring three different host races, or in a total of five geographically separated populations. There was also no significant association between host quality, as determined by species-specific female host body mass, and cuckoo sex ratio. Finally, we found no significant relationship between individual cuckoo maternal quality, as determined by her egg volume, and sex ratio within each host race. We conclude that the generalist brood-parasitic common cuckoo show no significant sex-ratio bias in relation to host race and discuss this finding in light of gene flow and host adaptations

First-Time Migration in Juvenile Common Cuckoos Documented by Satellite Tracking

Being an obligate parasite, juvenile common cuckoos Cuculus canorus are thought to reachtheir African wintering grounds from Palearctic breeding grounds without guidance fromexperienced conspecifics but this has not been documented. We used satellite tracking tostudy naïve migrating common cuckoos. Juvenile cuckoos left breeding sites in Finlandmoving slowly and less consistently directed than adult cuckoos. Migration of the juveniles(N = 5) was initiated later than adults (N = 20), was directed toward the southwest±significantlydifferent from the initial southeast direction of adults±and included strikingly long BalticSea crossings (N = 3). After initial migration of juvenile cuckoos toward Poland, themigration direction changed and proceeded due south, directly toward the winter grounds,as revealed by a single tag transmitting until arrival in Northwest Angola where northernadult cuckoos regularly winter. Compared to adults, the juvenile travelled straighter andfaster, potentially correcting for wind drift along the route. That both migration route and timingdiffered from adults indicates that juvenile cuckoos are able to reach proper winteringgrounds independently, guided only by their innate migration programme.</p

Are tits really unsuitable hosts for the Common Cuckoo?

Avian brood parasites exploit hosts that have accessible nests and a soft insect diet. Common Cuckoo (Cuculus canorus) hosts were traditionally classified as suitable if both parameters were fulfilled or unsuitable if one, or both, were not. In line with this view, hole-nesting tits (Paridae) have become a text-book example of unsuitable Cuckoo hosts. Our extensive literature search for Cuckoo eggs hatched and chicks raised by hosts revealed 16 Cuckoo nestlings in Great Tit (Parus major) nests, 2 nestlings and 2 fledglings in Blue Tits (Cyanistes caeruleus), and 1 nestling in a Crested Tit (Lophophanes cristatus) nest. Our own data from natural observations and cross-fostering experiments concur with literature data that Great Tits are able to rear Cuckoo chicks to fledging. The natural observations involve the first known cases where a bird species became parasitized as a byproduct of nest usurpation (take-over). Surprisingly, Cuckoo chicks raised by Great Tits grew better than Cuckoo chicks raised by common hosts, even alongside host own chicks. The frequency of Cuckoo parasitism in tits may be underestimated by studying tits in artificial nest-boxes with small entrances that prevent Cuckoos from laying and/or fledging. Results support a view that host suitability is not a categorical parameter (host suitable or unsuitable) but a continuous phenomenon. Understanding the diversity of parameters that determine host selection by Cuckoos is limited, because studies on Cuckoo chick diet, growth, and survival in most hosts are rare. Therefore any data are valuable and provide indispensable material for future meta-analyses