The white colour of the Ostrich ( Struthio camelus ) egg is a trade-off between predation and overheating

Most ground nesters lay pigmented eggs, and egg pigmentation generally matches the environment. Pigmentation of eggs has evolved as a protective device against predation, but dark-pigmented eggs can be susceptible to overheating when exposed to solar radiation. The Ostrich (Struthio camelus) lays white eggs that are unattended for the first few weeks before incubation, and are quite visible to predators. To evaluate the effect of colour on the surface and core temperatures, we painted some Ostrich eggs dark brown or white, and left some unpainted (control), and exposed all of them directly to the sun during the day. The surface and core temperatures of brown eggs were significantly higher than those of the white-painted and control eggs. In addition, the core temperature of brown eggs exceeded 37.5°C, which is the temperature at which embryo mortality starts to increase. In a second experiment, we placed eggs (brown-painted and control) in various types of vegetation to study their visibility to an observer walking towards them. The white eggs were discovered from a significantly longer distance than the brown eggs, indicating that the predation risk may be much higher for white eggs. The results thus suggest that white eggs minimise overheating and allow the Ostrich to leave its eggs unattended before incubation starts, but they are more susceptible to predation.     

Rejection of Conspecific Eggs in Chaffinches: The Effect of Age and Clutch Characteristics

Previous experimental studies have found that the majority of chaffinches, Fringilla coelebs, are able to reject both non‐mimetic and mimetic cuckoo eggs and also non‐mimetic conspecific eggs. However, interestingly the frequency of rejecters of moderately mimetic conspecific eggs has been found to be only approx. 50%. We examined the possibility that acceptors of moderately mimetic conspecific eggs are first time breeders, because these individuals may lack the experience needed to reject eggs that deviate only slightly from their own eggs. Older individuals, with good knowledge of their own egg appearance, should therefore reject such eggs. We also examined the possibility that acceptors of moderately mimetic eggs have a higher intraclutch variation in egg appearance, which makes it more difficult to recognize such eggs when compared with rejecters. We obtained no support for any age‐specific pattern in rejection behaviour. Furthermore, there was no relationship between age and intraclutch variation, or intraclutch variation and rejection behaviour. As there is no evidence of intraspecific brood parasitism in this species, the rejection of any foreign eggs is most probably an adaptation to past cuckoo, Cuculus canorus, parasitism. Acceptance of good and moderately mimetic conspecific eggs is probably due to cognitive limitations, because evolution of a more fine‐tuned recognition ability is unnecessary in the absence of intraspecific brood parasitism.     

Rejection of cuckoo (Cuculus canorus) eggs by meadow pipits (Anthus pratensis)

Meadow pipits (Anthus pratensis) normally accept mimetic cuckoo(Cuculus canorus) eggs laid in their nests. In field experimentsin which a mimetic or a nonmimetic model cuckoo egg was placedin meadow pipit nests, those hosts that were simultaneouslypresented with a cuckoo dummy mounted beside the nest showeda significantly higher ability to recognize and reject (normallyby desertion) the parasite's egg than those that were not presentedwith the dummy. In the present study we sought to answer thequestion of why meadow pipits do not always (i.e., even whenno cuckoo was visible) reject cuckoo eggs. The results fromthe field experiments provide support for a theory that two"brood parasite" stimuli (a cuckoo egg in the nest and a cuckoonear the nest) are necessary to induce the meadow pipits toreject cuckoo eggs. When the threshold for rejection had beenreached, the hosts reacted in a relatively short time afterthey were faced with the parasite stimuli. The results of theseexperiments also showed that a significantly higher rate ofrejection occurred earlier rather than later in the incubationperiod. A possible explanation for the higher rate of acceptanceof model cuckoo eggs among meadow pipits in Norway comparedto those in Britain is discussed.     

No evidence for recognition errors in Acrocephalus warblers

Failure to recognise own eggs (recognition errors) may be an important selective force behind acceptance of parasitic eggs, leading to a balance between rejecters and acceptors in a host population (the equilibrium hypothesis). We predicted that recognition errors should occur frequently among host species with intermediate rejection rates, whose rejection behaviour shows many conditional responses. The reed warbler Acrocephalus scirpaceus and great reed warbler A. arundinaceus fulfil these requirements. These two species were therefore used in an experiment where host birds were exposed to a common cuckoo Cuculus canorus dummy, either <2 m or 5–10 m from the nest, at fishponds in southern Moravia (Czech Republic). The hosts responded to the cuckoo dummy, great reed warblers being much more aggressive than reed warblers, and both species being more aggressive towards the dummy when it was close to the nest than when it was farther away. We furthermore predicted that there should be more eggs rejected (ejected or nest abandoned) due to recognition errors among hosts exposed to a dummy close to the nest than among both those exposed to a dummy farther away from the nest and towards controls not exposed to cuckoo dummies. When comparing egg loss between groups of birds that were exposed to a cuckoo dummy with those that were not, we found no significant difference. However, partial egg loss was frequent among hosts in the studied population, most probably due to cuckoo depredation. We discuss why there were no detectable recognition errors in the studied population, when other researchers have claimed to have found such errors in host populations elsewhere.     

Why do Red-winged Blackbrids accept eggs of Brown-headed Cowbirds?

Summary Avian brood parasites usually severely depress the reproductive success of their hosts, yet many host species, including those presumably capable of ejecting parasitic eggs, accept them. Female, brood-parasitic, Brown-headed Cowbirds typically remove a host egg when they lay their own and damage some host eggs in the process of ejecting a host egg. Data from a field study of Red-winged Blackbirds show that these costs, which cannot be avoided by ejecting the parasitic egg, account for some of the reproductive losses attributable to parasitism, but part is due to the presence of the cowbird egg in the nest. To assess whether ejection would be favoured under current circumstances, the probable damage a female Redwing could cause to her own eggs by attempting to eject a cowbird egg needs to be determined.     

Breeding ecology of Kori Bustard Ardeotis kori strunthiunculus in the Serengeti National Park

The breeding ecology of the Kori Bustard Ardeotis kori strunthiunculus was studied in the plains of the Serengeti National Park, Tanzania in 2014 and 2015. Random transects were used to search for male courtship displays, nests, chicks and subadults. GPS satellite collars were used to locate nesting females. Linear regression analyses and post hoc tests were used to determine the predictors that contributed most to the variation of the dependent variables (courtship display, nest, chicks and subadults). The results indicate that courtship behaviour peaks during the short dry and short rainy season before the peaks in nests and chicks. The highest nest frequency was found in short grass habitats. Female Kori Bustard may undergo repeated nestings within a single breeding season. The adult sex ratio was female skewed during the breeding season. The Kori Bustard breeding season in the Serengeti plains is relatively long, lasting for almost nine months, and taking place during all seasons except for the long dry season. We recommend that management authorities conduct assessments of Kori Bustard recruitment as well as habitat suitability in the Serengeti ecosystem to develop future conservation strategies.     

Importance of spatial habitat structure on establishment of host defenses against brood parasitism

We used metapopulation dynamics to develop a mathematical simulationmodel for brood parasites and their hosts in order to investigatethe validity of the "spatial habitat structure hypothesis,"which states that a low level of parasite egg rejection in hostpopulations is due to the immigration of acceptor individualsfrom nonparasitized populations. In our model, we varied dispersalrate and the relative carrying capacity of host individualsin parasitized and unparasitized patches. When both the relativecarrying capacity in the parasite-free patch and the dispersalrate increase, the nonparasitized patch will provide more acceptorindividuals to the parasite-prone patch. As the relative carryingcapacity in the parasite-free patch increases, the equilibriumfrequency of rejecters both in the parasite-prone and in theparasite-free patch decreases toward zero for intermediate levelsof the dispersal rate. Although the rejecter strategy is moreadaptive than the acceptor strategy in the parasite-prone patch,large numbers of acceptors are produced in the parasite-freepatch dispersing to the parasitized patch. As the number ofindividuals in the parasite-free patch increases, parasitismrate can be maintained stable at a high equilibrium level inthe parasite-prone patch.     

Determining adrenocortical activity as a measure of stress in African elephants (Loxodonta africana) in relation to human activities in Serengeti ecosystem

African elephants (Loxodonta africana) play a vital role in most African ecosystems, with their opportunity to alter the entire ecosystem by their sheer numbers. Defining and measuring animal welfare has been much discussed. One potential way of determining an animal's welfare is to record the absence or presence of stress. Little research on elephant welfare has so far been performed in the Serengeti ecosystem. The aim of this study was to record the faecal glucocorticoid metabolite levels of African elephants in areas with high or with minimum human interference. A total of 117 faecal samples were collected from randomly located single elephants as well as family herds in the northern, central and western Serengeti National Park (SNP) as well as in Grumeti Game Reserve and Ikoma Open Area, northern Tanzania in 2010. Elephants had higher levels of faecal glucocorticoid metabolites in the areas outside, compared with areas inside SNP. No single males were observed outside SNP, and in general, higher abundance of elephants was observed inside SNP. This suggests that elephants may prefer to reside in the potential safer areas inside the national park, demonstrating the importance of protected areas to improve the welfare of elephants.