Factors affecting vigilance within wild mixed-species troops of saddleback (<Emphasis Type="Italic">Saguinus fuscicollis</Emphasis>) and moustached tamarins (<Emphasis Type="Italic">S. mystax</Emphasis>)

We examine vigilance within a mixed-species troop of saddleback (Saguinus fuscicollis) and moustached (S. mystax) tamarins over a complete year. Saddleback tamarins were consistently more vigilant than moustached tamarins. This may be linked to their preference for lower strata. In accordance with previous studies of other primates, vigilant tamarins of both species were significantly further away from their nearest neighbours, and were also at lower heights in the forest than non-vigilant individuals. There was no observed sex difference in the amount of time spent vigilant. In terms of modes of scanning, the saddleback tamarins looked up significantly more frequently than the moustached tamarins, whereas there was no difference between the species in the frequency of side sweeps. There were no differences between the sexes in the frequencies of either type of vigilant behaviour. The proportion of time spent vigilant was higher than average immediately prior to entering a sleeping site for saddleback tamarins, but not for moustached tamarins. Both species were more vigilant immediately after exiting a sleeping site than at other times of the day. There was significant variation in the amount of time devoted to vigilance over the course of the year. These findings are discussed with respect to the social structure, ecology and main predator threats facing these species.Communicated by D. Watts     

Possible impact of sea-level rise on some habitat types at the Baltic coast of Denmark

According to estimates from the Danish Meteorological Institute global warming until 2080 may cause a relative sea-level rise in Danish waters of 33–46 cm. In the present paper the possible impact of a sea-level rise of this magnitude on coastal habitat types is discussed for three case studies, based on previous investigations of vegetation, topography and soil of localities at the Baltic coast of Denmark. The case studies include the following types of localities and habitats: (1) an off-shore barrier complex: sandy beach, sand dune, geolittoral, brackish, low-tidal meadow, reed bed; (2) a protected bay: geolittoral, brackish meadow, coastal grassland; (3) a dune area: mobile and fixed dune communities, and adjoining sea wall: coastal grassland. In the geolittoral meadow and coastal grassland habitats the sea-level rise is expected to cause a horizontal displacement of vegetation zones and a reduction in area, depending on accretion rate (sedimentation, peat formation), local topography and inland land-use. In the beach and sand dune habitats the sea-level rise is expected to cause a change in groundwater level, influencing slack vegetation, and a change in the erosion/accretion pattern, resulting in landward rebuilding of the mobile dune as well as in a more or less diffuse inland sand drift, causing destabilization of fixed dune vegetation.     

A study of the genetic relationships within and among wolf packs using DNA fingerprinting and mitochondrial DNA

Summary DNA fingerprinting and mitochondrial DNA analyses have not been used in combination to study relatedness in natural populations. We present an approach that involves defining the mean fingerprint similarities among individuals thought to be unrelated because they have different mtDNA genotypes. Two classes of related individuals are identified by their distance in standard errors above this mean value. The number of standard errors is determined by analysis of the association between fingerprint similarity and relatedness in a population with a known genealogy. We apply this approach to gray wolf packs from Minnesota, Alaska, and the Northwest Territories. Our results show that: (1) wolf packs consist primarily of individuals that are closely related genetically, but some packs contain unrelated, non-reproducing individuals; (2) dispersal among packs within the same area is common; and (3) short-range dispersal appears more common for female than male wolves. The first two of these genetically-based observations are consistent with behavioral data on pack structure and dispersal in wolves, while the apparent sex bias in dispersal was not expected.USA Offprint requests to: N. Lehman at the present address     

Is there a “sound window” for primate communication?

Summary It has long been asserted that habitat acoustics can determine the frequency band bestadapted for long-range communication, but the generality and validity of measurements claiming to demonstrate a window of best frequencies have recently been questioned. We report the discovery of a prominent sound window in Kenyan rain forest in a study that is free of methodological difficulties. Our results allow us to calculate the range advantage attained by an animal vocalizing within the sound window, and show that sound windows can be a potent factor for the evolution of primate communication.     

A ciliate red tide at Barrow,Alaska

In September 1968 the first occurrence of extensive red water in the Arctic Ocean in the vicinity of Point Barrow, Alaska, was recorded. The organism causing this water discoloration was a fairly large (100 to 150 ) ciliated protozoan, with chlorophyll-containing endosymbionts. This ciliate, which is not identical to the commonly reported Mesodinium or Cyclotrichium species, is described in this paper, but cannot be identified with any organism described in the literature. Concentrations of dissolved inorganic nutrients and trace metals were determined on water samples obtained from the red water and also in the clear water adjacent to it. These data are discussed relative to the hydrographic conditions in the Chuckchi Sea around Point Barrow. A direct species' analysis by microscopic methods indicated that the plankton were quite similar in all the water samples except for the aforementioned red ciliate, which accounted for over 90% of the total cellular organic carbon in the samples from the red water. Chemical analyses indicated that the red tide ciliate contained approximately 51% protein, 33% lipid, 8% carbohydrate, 0.2% chlorophyll a, and 1.2% DNA.     

Current versus future reproduction: an experimental test of parental investment decisions using nest desertion by mallards (<Emphasis Type="Italic">Anas platyrhynchos</Emphasis>)

Past investment in offspring may be important in determining a parent's ability to reproduce in the future and, hence, should affect the relative value of current offspring. However, there have been surprisingly few clear tests of whether animals actually adjust parental care in response to diminished opportunities for future reproduction. We modified the experimental protocol of Sargent and Gross [Behav Ecol Sociobiol (1985) 17:43–45] to examine offspring desertion by mallards ( Anas platyrhynchos), and decoupled the influence of past investment from expected current benefits by controlling for the effect of offspring age on clutch value. Using 9 years of nest mortality data, we accounted for the increasing prospects of egg survival with clutch age by calculating clutch sizes throughout incubation with equivalent expected benefits. Applying this approach, we experimentally reduced 203 clutches at two different incubation stages such that they had equivalent expected benefits but differed in the amount of past investment. Nest desertion rates did not differ between early- and late-incubated clutches that had equivalent expected benefits. Rather, the probability of desertion increased with the severity of the clutch reduction treatment. These results suggest that female mallards adjust parental care according to the expected benefits of current offspring, rather than to diminished prospects for future reproduction due to past investment. We further examined whether females assessed expected benefits on the basis of clutch size alone or clutch size adjusted for the age of the clutch. Using Akaike's Information Criterion, the most parsimonious model to explain the probability of deserting an experimentally reduced clutch included both the proportion of the clutch remaining and clutch age. Thus, female mallards appear to fine-tune their level of parental care not only according to the relative number of offspring in the clutch, but also to the increased prospects for offspring survival as they age.     

Twilight fighting in the evening brown butterfly,<Emphasis Type="Italic"> Melanitis leda</Emphasis> (L.) (Nymphalidae): age and residency effects

Butterflies are conspicuous among animals that fight for mating opportunities because it is not clear how contest costs could accrue. Nevertheless, the bulk of research in this group suggests that contests are settled on the basis of asymmetries in fighting ability (the superior competitor hypothesis). There is also a consistent effect on contest escalation due to apparent 'confusion' over residency, which could result from resident butterflies playing different tactics than non-residents, or from a causal link between residency and fighting ability. I addressed these hypotheses by studying contest behavior in the crepuscular species Melanitis leda (L.) (Nymphalidae) over a 5-month period in tropical Australia. Males competed via conspicuous two-stage maneuvers of a form unique among butterflies. Prior residents won 77% of all contests. Non-resident males arrived and perched in occupied sites until challenged by incumbent residents, and the aggressiveness of these interlopers increased as a function of the time before they were detected. Contest winners also tended to be younger than losers, and contest escalation was negatively related to both the age of the losing male and the magnitude of the between-combatant age asymmetry. These results are consistent with the superior competitor hypothesis based upon age as a determinant (or correlate) of fighting ability, but also suggest residency has a unique influence on contest behavior. Further research is clearly required to unravel the effects of age, residency and other potential biophysical determinants of fighting ability in this species.     

What limits predator detection in blue tits (<Emphasis Type="Italic">Parus caeruleus</Emphasis>): posture,task or orientation?

To detect threats and reduce predation risk prey animals need to be alert. Early predator detection and rapid anti-predatory action increase the likelihood of survival. We investigated how foraging affects predator detection and time to take-off in blue tits (Parus caeruleus) by subjecting them to a simulated raptor attack. To investigate the impact of body posture we compared birds feeding head-down with birds feeding head-up, but could not find any effect of posture on either time to detection or time to take-off. To investigate the impact of orientation we compared birds having their side towards the attacking predator with birds having their back towards it. Predator detection, but not time to take-off, was delayed when the back was oriented towards the predator. We also investigated the impact of foraging task by comparing birds that were either not foraging, foraging on chopped mealworms, or foraging on whole ones. Foraging on chopped mealworms did not delay detection compared to nonforaging showing that foraging does not always restrict vigilance. However, detection was delayed more than 150% when the birds were foraging on whole, live mealworms, which apparently demanded much attention and handling skill. Time to take-off was affected by foraging task in the same way as detection was. We show that when studying foraging and vigilance one must include the difficulty of the foraging task and prey orientation.Communicated by P.A. Bednekoff     

A field test of the intraspecific brood parasitism hypothesis in the golden egg bug (<Emphasis Type="Italic"> Phyllomorpha laciniata</Emphasis>)

In natural populations of golden egg bugs ( Phyllomorpha laciniata), females lay eggs on plants where they develop unattended, or on conspecifics, where they remain firmly glued until the nymphs hatch and start an independent life. Mortality rates among eggs laid on plants are higher than among eggs carried by adults. Because females cannot lay eggs on themselves, in order to improve offspring survival, they have to lay eggs on other individuals. Two hypotheses have been proposed to explain egg carrying: (1) the mating pair intraspecific brood parasitism hypothesis suggests that females dump eggs on copulating pairs, and (2) the paternal care hypothesis suggests that the system is driven mainly by males accepting eggs to improve the survival rates of their own offspring. Our data from the field show that 77% of the eggs are carried by males, because more males than females carry eggs, and because males carry a greater number of eggs. In addition, we show that mating males carry more recently laid eggs than single males. These results support the view that egg carrying is performed predominantly by males and that eggs are laid on males by their current mating partner, probably between repeated copulations. Males are likely to accept eggs, despite intermediate levels of paternity, because they cannot discriminate in favour of their own eggs, because rejected eggs will face 97% mortality rates on plants, and because they do not suffer mating costs when they carry eggs. However, females carry 23% of the eggs, but no differences in egg carrying have been found between mating and single females, suggesting that this is not the result of egg dumping while females are copulating. Egg carrying by females could reflect low levels of intraspecific parasitism, which is likely to reflect the low rate of successful attempts by egg-laying females who try to oviposit on other conspecifics rather indiscriminately, in an effort to improve the survival of their offspring.