Results of dyeing male yellow-headed blackbirds solid black: implications for the arbitrary identity badge hypothesis

Summary Territorial male yellow-headed blackbirds that were dyed solid black were similar to controls in their ability to attract mates. They also had no difficulty in defending their territories from floating males. The only remarkable effect of this dramatic color manipulation was that five of the 12 blackened males that regained a territory after being dyed also later took over the better quality territory of another male. Not one of the 11 control males that regained a territory succeeded in such an eviction. This surprising result is interpretable under the theory that conspicuous and distinctive coloration sometimes evolves as an arbitrary recognition badge by making good fighters more memorable to their opponents. With insight gained from these results, we modify and considerably expand the theoretical treatment of this Arbitrary Identity Badge Hypothesis. We also explain why our results for yellow-headed blackbrids should differ so dramatically from those for red-winged blackbirds where blackened males often lost their territories to floating males.     

Environmental conditions influence egg color of reed warblers <Emphasis Type="Italic">Acrocephalus scirpaceus</Emphasis> and their parasite,the common cuckoo <Emphasis Type="Italic">Cuculus canorus</Emphasis>

The outer layer of the eggshell in birds is in many cases covered by pigments that are assumed to be genetically determined traits with a negligible environmental component. To test the hypothesis that spring environmental conditions (i.e., temperature and rainfall) may affect bird egg pigmentation, we measured by spectrophotometry and photography egg coloration and spottiness on reed warbler (Acrocephalus scirpaceus L.) clutches parasitized by the common cuckoo (Cuculus canorus L.) collected over a period of 24 years and preserved in the Zoological Museum, Copenhagen, Denmark. In addition, we investigated whether spring environmental conditions may influence the coevolutionary relationship between the cuckoo and its host via changes in cuckoo–host egg matching. Generalized mixed models revealed that reed warbler eggs were more brilliant in those springs with a higher rainfall and tended to be bluer and greener in springs with a lower relative temperature. On the other hand, cuckoo eggs were bluer and greener in springs with a higher rainfall. Cuckoo–host egg matching in blue-greenness and spottiness was better in springs with a higher rainfall. These results provide support for the existence of an environmental component on bird egg coloration and suggest that environmental factors may potentially affect the outcome of important features of the arms race between cuckoos and reed warblers.     

The rarity of twins: a result of an evolutionary battle between mothers and daughters—or do they agree?

The aim of this study was to test the hypothesis that parent–offspring conflict over parental investment might have led to the rarity of dizygotic twins in humans. We explored the theoretical prediction that twins maximize their inclusive fitness by the death of a co-twin, while mothers of twins maximize fitness by raising both twins to independence. We used life history data (1700–1900) from two parishes in Central Norway to compare differences in inclusive fitness (measured as number of children reared to the age of 16 years, using Hamilton's rule) between twins and mothers of twins. Our results show that twins maximize their inclusive fitness by the death of a co-twin, while mothers of twins raise more children by rearing both twins to adulthood. However, because twins growing up as singletons may produce higher or at least equal number of offspring than the sum of the two twins growing up together, mothers might gain more grandchildren by allowing twins to grow up as singletons. To conclude, both selfish twins and their mothers might benefit by the death of a co-twin, indicating that there is no parent–offspring conflict responsible for the rareness of twins in these human populations. Finally, we discuss the results in the light of “The Insurance Egg Hypothesis” and “The Natural Selection Hypothesis”.     

Large carnivores and human safety: a review

Attacks by large carnivores on humans can occasionally help to generate significant resistance to carnivore conservation efforts. We have reviewed research addressing concerns for human safety in large carnivore conservation, and have evaluated statements about the frequencies and causes of attacks based on our findings concerning i) existing data on the number of attacks by large carnivores in various parts of the world; ii) information systems documenting details of attacks; and iii) research that provides credible advice on what to do when encountering a large carnivore, to minimize the likelihood of being attacked. We conclude that little information exists for any of these criteria and what is available is often inadequate to determine the frequency of attacks, their causes and how to avoid them. We suggest that information systems, including database(s) on attacks and encounters, should be established for large carnivore conservation efforts, to supply information and to answer future requests for this information.     

Host species affects the growth rate of cuckoo (Cuculus canorus) chicks

The cuckoo (Cuculus canorus) is an obligate interspecific brood parasite. When about to lay an egg, the female must decide which nest to parasitise. A high-quality host species should be preferred, to enhance the possibility of producing a viable offspring. In this study, we investigated the effects of two closely related host species, the great reed warbler (Acrocephalus arundinaceus) and the reed warbler (A. scirpaceus) on the growth rate of cuckoo nestlings. We found that cuckoo nestlings raised by the larger host species, the great reed warbler, grew significantly faster and became statistically significantly larger at fledging than nestlings raised by the smaller host, the reed warbler. Our results indicate a qualitative difference between the two host species. The great reed warbler, considered to be the best host, was parasitised at a higher rate than the reed warbler. Received: 2 February 1999 / Received in revised form: 3 September 1999 / Accepted: 18 September 1999     

Eggshell strength of an obligate brood parasite: a test of the puncture resistance hypothesis

Eggs of several brood parasites have thicker and stronger shells than expected for their size. The present study evaluated the puncture resistance hypothesis for the occurrence of thick-shelled eggs in common cuckoos Cuculus canorus by investigating costs of cuckoo egg ejection in four Acrocephalus warblers—the great reed warbler A. arundinaceus, reed warbler A. scirpaceus, marsh warbler A. palustris and sedge warbler A. schoenobaenus. The three latter species all suffered ejection costs, while ejection was not costly in the larger great reed warbler. The occurrence of ejection costs was negatively related to host bill size. In the marsh warbler, we compared ejection costs in naturally parasitized nests and two experimental treatments, in which broods were parasitized artificially with great reed warbler and conspecific eggs. Hosts damaged their own eggs significantly more often when ejecting the thick-shelled cuckoo eggs than when ejecting the similarly sized but thinner-shelled great reed warbler eggs, providing some support for the puncture resistance hypothesis. Ejection of conspecific eggs did not involve any costs. Furthermore, contrary to predictions derived from the laying damage hypothesis, there was no evidence that egg damage was associated with cuckoo egg laying. Hosts damaging their own eggs during ejection were more likely to subsequently desert their clutches than those that did not. The frequency of clutches smeared with the contents of the ejected egg were positively related to the hypothesized difficulty of foreign egg puncturing. Potential advantages of thicker shells in common cuckoo eggs are discussed.     

大型食肉动物与人类的安全:综述

人类遭大型食肉动物袭击有时会造成对食肉动物保护工作的强大的抵触情绪.我们回顾了在大型食肉动物保护工作中致力于解决人类安全问题的研究工作,并在我们所得到的如下几方面的调查结果的基础上,对有关遭袭击的频率和原因方面的陈述进行评估:①有关在世界不同地区遭大型食肉动物袭击次数的资料;②提供遭袭击细节的信息系统;③就遭遇大型食肉动物时如何应对的问题提出可靠建议的研究工作,目的是尽量减少遭袭击的可能性.我们的结论是,上述各标准中的现存信息很少,并且现有的信息往往不足以确定袭击的频率、袭击的原因以及如何避免上述袭击.我们建议为大型食肉动物保护工作建立信息系统(包括有关人类遭袭击和人类与食肉动物相遇的数据库),以便提供相关信息并满足将来对这些信息的需求.     

Evolution of variation in male secondary sexual characteristics

Summary The male pied flycatcher Ficedula hypoleuca exhibits sexual dimorphism in its plumage colour, varying from a female-like brown to jet black. The evoltution of this variation in male plumage colour can be explained by at least eight hypotheses viz., (I) neutral mutation; (II) individual recognition; (III) three forms of inter-sexual selection; (IIIa) mate selection for phenotypes, (IIIb) Fisherian selection, (IIIc) handicap selection; (IV) intrasexual selection; (V) delayed maturation; and (VI) female mimicry. The assumptions and predictions derived from all these hypotheses were tested by analysing the observed variation in male plumage colour in relation to age, body size, physical condition, survival rate, aggressivity in territorial defence, territorial quality, female choice of mate, sex ratio, and reproductive success. We found that: males became blacker with age; black males were larger than browner ones; however, browner males survived better between breeding seasons than did blacker ones; black males were more aggressive against black than brown intruders; blacker males occupied better territories; blacker males were paired earlier than browner males; and finally blacker males produced heavier offspring than did brown males. A reasonable conclusion from the results of these analyses is that four of the hypotheses considered, viz. mate selection for phenotypes (IIIa), Fisherian selection (IIIb), handicap selection (IIIc), and intra-sexual selection (IV) could not be rejected. We therefore suggest that the evolution of the observed variation in the secondary sexual characteristics of the male pied flycatcher can be explained by a combination of these hypotheses.     

First evidence of regular common cuckoo, <Emphasis Type="Italic">Cuculus canorus</Emphasis>, parasitism on eastern olivaceous warblers, <Emphasis Type="Italic">Hippolais pallida elaeica</Emphasis>

Coevolution is defined as specialized relationships between species that lead to a reciprocal evolutionary change. A particularly suitable model system for studying coevolution is the interactions between obligate avian brood parasites and their hosts. The common cuckoo (Cuculus canorus, hereafter cuckoo) is a well-known brood parasite, which utilizes a range of smaller passerines as hosts. However, warblers of the genus Hippolais have rarely been reported as being victims of cuckoos, and furthermore, few data exist on the occurrence of antiparasite defenses in these hosts. In this study, we examined possible host–parasite coevolution between cuckoos and eastern olivaceous warblers (Hippolais pallida elaeica, hereafter olivaceous warblers) in three closely situated areas in northwestern Bulgaria. The olivaceous warbler has never been reported to be a regular cuckoo host. However, the present study, carried out in 2001–2003 shows that the olivaceous warbler is regularly and heavily parasitized by the cuckoo in this area. Parasitism rate was high (26.6%, 34/128) and consistent among years, with some variation between areas. The cuckoo egg mimicry was moderately good, and olivaceous warbler rejection rate of such eggs was 50%. Cuckoo eggs laid in olivaceous warbler nests had a whitish to whitish-green ground color, and the majority appeared to be distinctly different from cuckoo eggs found in other host species in the area. The olivaceous warbler proved to be a rather good host for cuckoos as 20.6% (7/34) of cuckoo eggs laid produced fledglings, a breeding success comparable to other suitable hosts in Europe. This is the first in-depth study of brood parasitism in a warbler of the genus Hippolais, and cuckoos parasitizing olivaceous warblers probably represent a previously unknown gens.