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.

Rapid change in host use of the common cuckoo Cuculus canorus linked to climate change.

Parasites require synchrony with their hosts so if host timing changes with climate change, some parasites may decline and eventually go extinct. Residents and short-distance migrant hosts of the brood parasitic common cuckoo, Cuculus canorus, have advanced their phenology in response to climate change more than long-distance migrants, including the cuckoo itself. Because different parts of Europe show different degrees of climate change, we predicted that use of residents or short-distance migrants as hosts should have declined in areas with greater increase in spring temperature. Comparing relative frequency of parasitism of the two host categories in 23 European countries before and after 1990, when spring temperatures in many areas had started to increase, we found that relative parasitism of residents and short-distance migrants decreased. This change in host use was positively related to increase in spring temperature, consistent with the prediction that relative change in phenology for different migrant classes drives host-use patterns. These findings are consistent with the hypothesis that climate change affects the relative abundance of different host races of the common cuckoo.

[Involution of the uterus following vaginal or abdominal delivery]. / Uterusrückbildung nach vaginaler und abdominaler Entbindung.

Involution of the uterus was observed in 77 puerperae by B-scan ultrasonography. In most cases the examinations were carried out several times on different days. Of all uterine dimensions (extension, circumferences, areal dimensions, volume index) the length proved particularly suitable for evaluating the involution. The other parameters offered no advantages. The findings covered 60 examinations following spontaneous labor and 137 following cesarean section. In both groups involution was completed by the 6th to 7th week after parturition. On the basis of mean values the course of involution was identical in the two groups, although there was considerable individual scatter. These findings, which do not correlate to the usual palpation findings in daily fundus checks on puerperae, may be explained by the different position of the uterus. Following spontaneous labor there is pronounced anteversion of the uterus and it is located lower. Following cesarean section it adopts a more extended position causing the fundus to be higher on palpation. It was also found that daily intramuscular injection of Syntocinon following cesarean sections has no measurable influence on the rate of involution.