Arnon Lotem



Publications with abstracts                                               Return to my home page



Shafir S, Reich T, Tsur E, Erev I, and Lotem A. 2008. Perceptual accuracy and conflicting effects of certainty on risk-taking behaviour. Nature 453: 917-920  Full Text | PDF (221K) See also: Making the paper: Arnon Lotem Nature podcast: interview with Ido Erev media coverage  

Abstract: The 'certainty effect'1, 2 is a notable violation of expected utility theory by decision makers3, 4, 5, 6. It shows that people's tendency to select the safer of two prospects increases when this prospect provides a good outcome with certainty (for example, people prefer a monetary gain of 3 with certainty over 4 with a probability of 0.8, but do not prefer 3 with a probability of 0.25 over 4 with a probability of 0.2). Subsequent work on experience-based decision making in rats7 extended the certainty effect to other animals, suggesting its generality across different species and different decision-making mechanisms. However, an attempt to replicate this study with human subjects showed a surprising 'reversed certainty effect'8, 9, namely, the tendency to prefer the safer option decreases when this prospect is associated with certainty (and people now prefer 4 with a probability of 0.8 over 3 with certainty). Here we show that these conflicting results can be explained by perceptual noise and that the certainty effect can be restored experimentally by reducing perceptual accuracy. Using complementary experiments in humans and honeybees (Apis mellifera), we show that by manipulating perceptual accuracy in experience-based tasks, both the certainty and the reversed certainty effects can be exhibited by humans and other animals: the certainty effect emerges when it is difficult to discriminate between the different rewards, whereas the reversed certainty effect emerges when discrimination is easy. Our results fit a simple process-based model of matching behaviour10, 11, capable of explaining the certainty effect in humans and other animals that make repeated decisions based on experience. This mechanism should probably be distinguished from those involved in the original certainty effect that was exhibited by human subjects in single description-based problems1, 2.


Lotem A. and Halpern J.Y. 2008 A Data-Acquisition Model for Learning and Cognitive Development and Its Implications for Autism. Cornell Computing and Information Science Technical Reports Abstract PDF

Abstract: A data-driven model of learning is proposed, where a network of nodes and links is constructed that represents what has been heard and observed. Autism is viewed as the consequence of a disorder in the data-acquisition component of the model---essentially, it is the result of getting an ``inappropriate'' distribution of data. The inappropriate data distribution leads to problems in data segmentation, which, in turn leads to a poor network representation. It is shown how the model, given inappropriate data distributions, can reproduce the main cognitive deficits associated with autism, including weak central coherence, impaired theory of mind, and executive dysfunction. In addition, it is shown how the model itself can explain the inappropriate data distribution as the result of an inappropriate initial network. Finally, we discuss the relationships between our model and existing neurological models of autism, and the possible implications of our model for treatment.


Uri Grodzinski, Ido Erev, and Arnon Lotem 2008. Can hungry nestlings be trained to reduce their begging? Behavioral Ecology  19: 116-125 PDF


Abstract: Nestling begging behavior is usually characterized by a behavioral response of increasing begging levels with an increase in nestling need or hunger. Recent evidence for the possible effect of learning on begging intensity raises the question of how learning can shape this response rule. In particular, it is not clear whether hungry nestlings can learn to reduce their begging when it is not successful or, rather, whether they must first acquire positive experiences with low begging levels in order to do so. To explore this question, we conducted 3 hand-feeding experiments with pairs of house sparrow (Passer domesticus) nestlings. In the first 2 experiments, the nestlings targeted to lower their begging were rewarded mainly or only for low begging postures. However, despite the high expected reward for low begging, these nestlings did not lower their begging. Controlled by their behavioral response function, hungry nestlings were "stuck" at high postures without being able to experience the potential success of low postures. In the third experiment, nestlings targeted to lower their begging levels were rewarded for any begging posture, ensuring that satiation would provide their initial "positive experience" with low begging postures. Begging postures were reduced by this treatment. In light of these results, we suggest that parents are unlikely to reduce offspring begging levels by simply ignoring them. However, they might be able to do so by attending to the begging as soon as possible, thereby allowing their offspring to explore low begging and learn that it is sufficiently effective.



Katsnelson E, Motro U, Feldman MW, and Lotem A. 2008. Early experience affects producer–scrounger foraging tendencies in the house sparrow. Animal Behaviour, In press. (Available online November 19, 2007) PDF


Abstract: Group foragers can use a ‘producer’ tactic which involves searching for food or a ‘scrounger’ tactic which involves joining others who have discovered food. While these alternative behaviours are well documented, it is not clear to what extent an individual's tendency to forage independently or to follow others is under genetic control or rather is affected by experience. To examine whether hand-reared juveniles can learn to prefer using a producer or a scrounger tactic, we hand-reared house sparrow, Passer domesticus, nestlings that upon fledging were assigned to one of two training groups; the first was expected to enhance joining (scrounging) behaviour and the second to enhance searching (producing) behaviour. In the first group, fledglings were imprinted on a parent model (stuffed female sparrow) that visited locations containing food. In the second group, fledglings were imprinted on a parent model that visited locations containing no food, while food was available in different locations. At the end of a 5-day training phase, all fledglings were released into a shared aviary, and their social foraging tendencies were measured. We found that fledglings from the first group used significantly more joining behaviour than fledglings from the second group, suggesting that an individual whose early experience positively reinforced joining behaviour is more likely to later become a joiner. To our knowledge, this is the first experimental evidence for the effect of learning on the choice between social foraging strategies in the context of the producer–scrounger game.



Adar E, Lotem A. and A. Barnea 2008. The effect of social environment on singing behavior in the zebra finch (Taeniopygia guttata) and its implication for neuronal recruitment. Behavioural Brain Research 187: 178-84 (Available online 17 September 2007) PDF


Abstract: Previous studies found that complex social environment increases new neuronal recruitment in brains of adult male zebra finches, in comparison with exposure to a simple social environment. These experiments could not determine, however, whether this increase was due to greater amounts of auditory input (amount of auditory information the male is exposed to), or auditory output (amount of song it produces). To answer this question, we raised male zebra finches to adulthood in a controlled environment, and were then exposed them to either a single unfamiliar female (simple social environment) or to 45 unfamiliar zebra finches of both sexes (complex social environment). Their singing behavior was monitored in these new social environments. Birds which were exposed to a simple social environment sang significantly more than birds which were exposed to a complex social environment. This supports the hypothesis that increased neuronal recruitment in birds exposed to a complex social environment correlates with processing and storing of auditory input, and not with song produced by the bird.



Grodzinski U, Lotem A. 2007. The adaptive value of parental responsiveness to nestling begging. Proceedings of the  Royal  Society of  London B.  274 (1624): 2449-56 PDF


Abstract: Despite extensive theoretical and empirical research into offspring food solicitation behaviour as a model for parent–offspring conflict and communication, the adaptive value of parental responsiveness to begging has never been tested experimentally. Game theory models, as well as empirical studies, suggest that begging conveys information on offspring state, which implies that parental investment can be better translated to fitness by responding to begging when allocating resources rather than by ignoring it. However, this assumption and its underlying mechanisms have received little or no attention. Here we show by experiments with hand-raised house sparrow (Passer domesticus) nestlings that a ‘responsive parent’ will do better than a hypothetical ‘non-responsive’ mutant (that provides similar food amounts, but irrespective of begging). This is neither because food-deprived nestlings convert food to mass more efficiently, however, nor because responsiveness reduces costly begging. Rather, responsiveness to begging is adaptive because it reduces two opposing risks: one is wasting time when returning too soon to feed already satiated nestlings and the other is repeatedly overlooking some nestlings as a result of the stochastic nature of a random, non-responsive strategy. This study provides the first experimental evidence for the adaptive value of parental responsiveness to offspring begging.



Dor R., Kedar H., Winkler WD. & Lotem 2007. Begging in the absence of parents: a "quick on the trigger" strategy to minimize costly misses. Behavioral Ecology, 18: 97-102  PDF


Abstract: Nestling begging in the absence of parents may reflect ‘‘false alarms’’ due to cognitive constraints or signaling activity toward nest mates (sibling negotiation).According to signal detection theory, cognitive constraints should result in both false alarms (begging in the absence of parents or to inappropriate stimuli)and misses (failure to beg during parental visits).In our study of house sparrows, nestling begging in the absence of parents comprised up to 50%of the begging events at the nest and was more frequent at an early age and among hungrier (lower ranked)nestlings. In contrast, the probability of begging during parental visits was constantly high (80%or more), suggesting that the rate of misses must have been low even at an early age. These results have 2 main implications. First, the observation that begging in the absence of parents decreases with nestling age favors the cognitive constraints hypothesis over functional explanations such as the sibling negotiation hypothesis. Second, the low proportion of ‘‘misses’’ among young nestlings suggests that nestling respond to their cognitive constraints by using low decision criteria (a ‘‘quick on the trigger’’ strategy) that increases the frequency of false alarms but minimizes costly misses.



Munichor N., Erev I. & Lotem A. 2006 Risk attitude in small timesaving decisions. Journal of Experimental Psychology: Applied. 12: 129-141. PDF


Abstract: Four experiments are presented that explore situations in which a decision maker has to rely on personal experience in an attempt to minimize delays. Experiment 1 shows that risk-attitude in these timesaving decisions is similar to risk-attitude in money-related decisions from experience: A risky prospect is more attractive than a safer prospect with the same expected value only when it leads to a better outcome most of the time. Experiment 2 highlights a boundary condition: It suggests that a difficulty in ranking the relevant delays moves behavior toward random choice. Experiments 3 and 4 show that when actions must be taken during the delay (thereby helping compare delays),this increases the similarity of timesaving decisions to money-related decisions. In these settings the results reflect an increase in risk aversion with experience. The relationship of the results to the study of non-human time-related decisions, human money-related decisions and human time perception is discussed.




Werner N.Y. & Lotem A. 2006.  Experimental evidence for male sequential mate preference in a lekking species. Ethology 112: 657-663. PDF


Abstract: In lekking species females visit male aggregations solely to copulate or have their eggs fertilized. Because lekking males do not contribute to parental care, evolutionary theory does not expect them to be choosy. However, we show here that in the cichlid fish Astatotilapia flaviijosephi the lekking males exhibit sequential mate preference that strongly suggests a trade-off between present and future reproductive effort. We tested mate preferences of A. flaviijosephi males by sequentially presenting them with two images of a gravid female, differing only in size. Previously, males were shown to prefer larger, more fecund females in simultaneous preference tests. The sequential presentation experiment reported here indicates that even in the absence of simultaneous presentation, males spent more time courting larger female images, and stayed longer in their vicinity. Thus, our study suggests that lekking males may be much choosier than previously appreciated. Furthermore, considering the intense competition among lekking males we also suggest that male choosiness, combined with other factors, may help to solve the 'paradox of the lek'. It can make less attractive females more available to subordinate males, thereby increasing the contribution of the latter to the population gene pool and keeping genetic variability among males at a level that justifies female choice.



Ben-Dov A., Vortman Y. & Lotem A. 2006. First documentation of sibling cannibalism in a small passerine species. Ibis 148: 365-367. PDF

No abstract. In this paper, we report on a female House Sparrow, Passer domesticus, caught on video camera feeding her nestlings with the carcass of their dead sibling.  See video clip at:



Lotem A. & Winkler DW. 2005 Defining the Concept of Public Information. Science  308: 354. PDF (no abstract)



Lotem A. & Winkler DW. Can reinforcement learning explain variation in early infant crying? Behavioral and Brain Sciences  27: 468. (PDF version)


Abstract: We welcome Soltis' use of evolutionary signaling theory, but question his interpretations of colic as a signal of vigor and his explanation of abnormal high-pitched crying as a signal of poor quality. Instead, we suggest that these phenomena may be sub-optimal by-products of a generally adaptive learning process by which infants adjust their crying levels in relation to parental responsiveness.




Werner N.Y., Balshine-Earn S., Leach B. & Lotem A. Helping opportunities and space segregation among helpers in co-operatively breeding cichlid. Behavioral Ecology 14:749–756. (PDF version)

Abstract: Studies of cooperative breeding have largely ignored the role of conflict among helpers and how it shapes group dynamics and helping behavior. In this study, using laboratory experiments with cooperatively breeding cichlids from Lake Tanganyika, we show that secondary group members (potential helpers) occupy home ranges within the group territory and may be aggressive to one another. Experimental removal of secondary group members allowed the individual next in rank to move closer to the removed individual’s home range. In the field, dominant secondary group members stayed closer to the brood chamber than subordinate group members of similar size, and proximity to the brood chamber was related to the length of time spent inside. We suggest that space segregation and competition among secondary group members may be common in these cichlids, and may limit the opportunities to provide help.


Fishman MA, Stone L & Lotem A. 2003  Fertility assurance through extrapair paternity, and male paternity defense. J. Theor. Biol. 221:96-107. (PDF version

Abstract: Extrapair paternity has been observed in many formally monogamous species. Male pursuit of extrapair fertilizations is explained by the advantages of having offspring that receive essential paternal care from other males. Since females are capable of exercising a degree of control over the post copulatory sperm competition, extrapair paternity cannot persist unless it confers fitness benefits on cuckolding females. Thus, extrapair paternity involves cooperation between mated females and extrapair males. On the other hand, paired males frequently exhibit strategies that minimize their loss of paternity and/or conserve paternal investment if paternity is lost. Hence, extrapair attributes of diverse species and populations reported in the literature are particular solutions of evolutionary games involving gender-specific cuckolding/anti-cuckolding strategies. Here we use methods of evolutionary game theory to study the role of male paternity guarding strategies in situations where females seek extrapair fertilizations for reasons of genetic compatibility and/or in pursuit of genetic diversity for their offspring. Our results indicate that in these circumstances pursuit of extrapair fertilizations is the only evolutionary stable female strategy. Males, on the other hand, have two, mutually exclusive, evolutionary stable strategies: full time pursuit of extrapair fertilizations and a compromise strategy wherein they protect in-pair paternity during their mate’s fertile periods and pursue extrapair paternity the rest of the time. The relative merits of these two strategies are determined by the efficiency of male in-pair paternity defense, breeding synchrony, fitness advantages of extrapair over in-pair offspring, and the intensity of competition for extrapair fertilizations from floater males.


Werner N.Y. & Lotem A. 2003  Choosy males in a haplochromine cichlid: first experimental evidence for male mate choice in a lekking species. Anim. Behav. 66:293–298. (PDF version)

Abstract: Current theories of mate choice predict that the level of choosiness exhibited by the different sexes will depend on their relative investment in parental care. Females often invest more than males (both in the pre- and post-zygotic stages), and are therefore expected to be the choosier sex. Males, on the other hand, are expected to be less choosy, especially in lekking species where males contribute nothing but sperm to reproduction. In these latter species males have often been found to mate indiscriminately with as many receptive females as possible. In contrast, our study of the haplochromine cichlid fish Astatotilapia flaviijosephi, a maternal mouth-brooder, provides the first experimental evidence for male mate choice in a lekking species. In this species the number of eggs spawned correlates positively with female weight, thus, making larger females potentially better mates. Our experiments indeed demonstrated that A. flaviijosephi males prefer to court the larger of two females when given a simultaneous choice. Furthermore, males spent more time courting during experimental trials involving larger females. This selective allocation of courtship effort to more attractive (i.e. heavier) females suggests that there may be constraints on males in fertilizing multiple females, thus compelling them to be choosy.


Lotem A, Fishman M.A., & Stone L. 2003 From reciprocity to unconditional altruism through signaling benefits. Proc. Roy. Soc. Lond. B. 270:199-205. (PDF version).


Abstract: Cooperation among genetically unrelated individuals is commonly explained by the potential for future reciprocity or by the risk of being punished by group members. However, unconditional altruism is more difficult to explain. Here we show that unconditional altruism can evolve as a costly signal of individual quality (i.e. a handicap) as a consequence of reciprocal altruism. This is because the emergent correlation between altruism and individual quality in reciprocity games can facilitate the use of altruism as a quality indicator in a much wider context, outside the reciprocity game, thus affecting its further evolution through signaling benefits. Our model, based on multitype evolutionary game theory, shows that when the additive signaling benefit of donating help exceeds the cost for only some individuals (of high quality state) but not for others (of low quality state), the population possesses an ESS profile wherein high quality individuals cooperate unconditionally while low quality individuals defect or play TfT. Hence, as predicted by Zahavis handicap model, signaling benefits of altruistic acts can establish a stable generosity by high quality individuals which no longer depends on the probability of future reciprocation or punishment.

Ovadia O, Pinshow B. & Lotem A. 2002 Thermal imaging of house sparrow nestlings: the effect of begging behavior and nestling rank. The Condor 104:837
842. ( PDF version)

Abstract: We used infrared imaging to test whether the energetic cost of begging is observable in changes in body surface temperature (Ts) of young House Sparrow nestlings (Passer domesticus), and whether Ts is affected by nestling rank. Begging had a mixed effect on Ts, increasing it slightly at first, but decreasing it when hungry nestlings begged more vigorously. This mixed effect may result from heat production being quickly offset when begging posture and movement enhance heat loss through the skin, and suggests that the energetic cost of begging cannot be inferred from thermal imaging. The analysis of Ts in relation to nestling rank showed that although low-ranked nestlings maintained lower Ts than their larger siblings, their Ts was higher than expected for their body mass. This suggests that nestlings of a lower rank may gain heat from their larger, more developed nestmates.

Fishman M.A., Lotem A & Stone L. 2001 Heterogeneity stabilizes reciprocal altruism interactions. J. Theor. Biol. 209, 87-95. (PDF version)

Abstract: In considering the phenomena of reciprocal altruism few would dispute that there are differences in individual quality-in particular, that for some individuals, at least on occasion, the cost of doing favors will exceed the potential of future benefits. That is, at any given time, a typical population is heterogeneous with respect to the affordability of reciprocal altruism. However, methodological limitations of the traditional analytical framework-Single Type (symmetric) Evolutionary Game Theory-have restricted previous analytical efforts to addressing populations idealized in terms of their averages. Here we use the methods of Multitype Evolutionary Game Theory to analyze the role of individual differences in direct reciprocity interactions. Multitype analysis shows that non-idealized populations possess an ESS profile wherein individuals who cannot afford reciprocity (low quality) defect, while individuals who derive net benefits from reciprocity (high quality) cooperate. Furthermore, this cooperation is implemented via unmodified Tit-for-Tat strategy. Hence our results may help resolve a long-standing problem concerning the evolutionary stability of Tit-for-Tat in direct reciprocal altruism. Finally, this difference between idealized and real populations is not restricted to direct reciprocal cooperation. Previously (Lotem et al., 1999) we have demonstrated evolutionary stable indirect reciprocal cooperation among high quality individuals in heterogeneous populations.

Kedar H., Rodriguez-Girones M., Yedvab S., Winkler DW & Lotem A. 2000. Experimental evidence for offspring learning in parent-offsrping communication. Proc. Roy. Soc. Lond. B. 267, 1723-1727. (PDF version)

Abstract: The offspring of birds and mammals solicit food from their parents by a combination of movements and vocalizations that have come to be known collectively as `begging'. Recently, begging has most often been viewed as an honest signal of offspring need. Yet, if offspring learn to adjust their begging efforts to the level that rewards them most, begging intensities may also reflect offsprings' past experience rather than their precise current needs. Here we show that bird nestlings with equal levels of need can learn to beg at remarkably different levels. These experiments with hand-raised house sparrows (Passer domesticus) indicated that chicks learn to modify begging levels within a few hours. Moreover, we found that the begging postures of hungry chicks in natural nests are correlated with the average postures that had previously yielded them parental feedings. Such learning challenges parental ability to assess offspring needs and may require that, in response, parents somehow filter out learned differences in offspring signals.

Lotem A., Fishman A. M., & Stone L. 1999. Evolution of cooperation between individuals.Nature 400:226-227. (PDF version) (see for an electronic appendix)

Abstract: Nowak and Sigmund(1) conclude that cooperation may have evolved through indirect reciprocity by image scoring. Their simulations and analytical models(1,2) predict long term cyclical dynamics between cooperative and defector populations rather than an evolutionarily stable equilibrium. Here we add a realistic feature to their model: that there are always some individuals unable to cooperate owing to their poor phenotypic condition (we call these individuals ('phenotypic defectors'). The presence of phenotypic defectors paradoxically allows persistent discriminating cooperation under a much wider range of conditions than found by Nowak and Sigmund because there is selection against both defection and unconditional altruism. In real populations there will nearly always be some level of defection because phenotypic defectors such as the young, sick or handicapped) may be unable to help even if they have a genetic predisposition to do so.

Rodriguez-Gironez M., Lotem A. 1999, How to detect a cuckoo egg: a signal detection theory model for recognition and learning. Amer. Natur. 153: 633-648. (PDF version)

Abstract: This article presents a model of egg rejection in cases of brood parasitism. The model is developed in three stages in the framework of signal-detection theory. We first assume that the behavior of host females is adapted to the relevant parameters concerning the appearance of the eggs they lay. In the second stage, we consider the possibility that females make perceptual errors. In the final stage, females must learn to recognize their own eggs through an imprinting process. The model allows us to make a number of predictions concerning the egg types that should be rejected in different circumstances: egg rejection should increase as the parasitism rate increases and egg mimicry deteriorates; host females' erroneous ejection of their own eggs should be expected for intermediate levels of egg mimicry but not for very good or very poor mimicry; host females would benefit most from learning to recognize their own eggs when individual variability in egg characteristics is much lower than the population variability; and, when egg mimicry is poor or individual variability is very low, females should attempt to imprint on the first egg they lay, before they can be parasitized, but, when mimicry is good and individual variability is relatively high, females must use an extended learning phase. The model provides a framework to study how the enigmatic acceptance of parasitic eggs can be explained by adaptive discrimination mechanisms.

Lotem A. Wagner R.H. & Balshine-Earn S. 1999, The overlooked signaling component in non-signaling behavior. Behavioral Ecology. 10: 209-212. (PDF version)

Abstract: Despite the general acceptance that the handicap principle explains extravagant morphological and behavioral signals, the model's mechanism has not been applied to explain quantitative variations in non-signaling behaviors. We suggest that animals may be selected to perform many behaviors differently when they are observed by other animals, and that such changes in the level or the intensity of a behavior can shift the behavior from its non-signaling optimum. As a result, many behaviors that are not defined as signals may nevertheless evolve a signaling component that affects them quantitatively rather than qualitatively. We explore this issue using examples from prey fleeing from a predator, human behavior in the presence of others, and parental care behavior. We then apply the overlooked signaling component of behaviors to illustrate that helping behavior among kin, which increases inclusive fitness, also may eventually evolve into signals of individual quality, condition, or need.

Lotem A. 1999 Manipulative begging by parasitic cuckoo nestlings and paradoxical host behaviour: a reply to Redondo. Trends in Ecology and Evolution. 14: 107. (PDF version)

Abstract: I welcome Redondo's clarification that Davies et al.'s new finding(1) can be viewed as a specific case of his Manipulative Interference Model(2) (MIM). My suggestion that Davies et al.'s study provides a 'different answer' related to the precise way in which cuckoo chicks manipulate their hosts, not in questioning whether they do so. Regarding the title question of my article 'Why should true offspring not do the same?': there is no doubt that because of the lack of genetic relatedness parasitic nestlings are expected to beg more(3-5). However, because we cannot feasibly predict how much more, we cannot determine if this is the only reason; perhaps there are additional ones. Being satisfied with the immediate and obvious explanation, as suggested by Redondo, might not be the most productive methodology, because it weakens the motivation to consider alternatives or to look for additional factors

Lotem A. 1998. Manipulative begging calls by parasitic cuckoo chicks: why should true offspring not do the same? Trends in Ecology and Evolution. 13: 342-343. (PDF version)

Abstract: The long-standing puzzle of how cuckoo chicks deceive their foster parents(1-4) continues to challenge evolutionary biologists. Although the host's inability to discriminate among nestlings can be explained as a result of an evolutionary lag(1-3) or learning constraints(5), the tendency to feed any nestling at the nest does not explain how the single chick of the common cuckoo (Cuculus canorus) extracts food from its foster parents at a rate comparable to that of a whole brood of host young(6). A new study(7), using reed warbler hosts (Acrocephalus scirpaceus), suggests that cuckoo chicks trick their foster parents by using begging calls that mimic the sound of a whole brood. This finding provides an exciting explanation for how the cuckoo deceives its host but also challenges our view of nestling begging as honest signals of offspring need(8,9). If cuckoo chicks can use manipulative begging calls, why have normal chicks not evolved similar adaptations to exploit their parents? Although there are certain hints in the literature that suggest possible answers, the issue is still unresolved.

Lotem A. 1998. Differences in begging behaviour among barn swallow (Hirundo Rustica) nestlings. Anim. Behav. 55:809-818. (PDF version)

Abstract: Recent models of parent-offspring communication suggest that nestling begging reliably reflects food requirements, and therefore should increase with nestling need. Need may be affected by short-term variations in hunger, as well as by long-term factors such as relative size, growth rate and body condition. In the present study, the brood sizes of barn swallows were manipulated to create differences in nestling growth rate and body condition. The extent to which begging behaviour reflects these differences was tested. I measured begging behaviour by removing nestlings from the nest for three laboratory tests in which temporal variations in hunger were controlled, and four target nestlings (small and large, from small and large broods) were tested simultaneously. Small nestlings and nestlings from large broods had lower growth rates and poorer body condition than large nestlings and nestlings from small broods, respectively. Begging was positively correlated with both short- and long-term determinants of need. However, when nestlings grew older (second test), the trend was mixed, mainly because begging levels dropped in the neediest nestling category (small nestlings from large broods). After nestlings had been exchanged between broods for 24 h, small nestlings from large broods improved their growth rate and body condition, but still begged less than expected from their long-term need. The results suggest that nestling begging strategies vary with brood size and with nestling rank. However, these variations may reflect not only long-term need, but also nestling response to past experience or to variations in the cost and effectiveness of their begging efforts.

Lotem A. 1998. Brood reduction and begging behaviour in the Swift Apus apus; no evidence that large nestlings restrict parental choice. Ibis 140:507-511.

Abstract: Brood reduction in birds is generally viewed as an adaptive process by which parents can maximize reproductive success in the face of an unpredictable environment. However, brood reduction may not be adaptive for the parents if the reduction is instead caused by large nestlings that block the nest entrance, thereby restricting parental choice, To determine the degree of difficulty faced by the parents in obtaining access to their smallest nestlings, a simple experiment was conducted in the Swift Apus apus. By inserting a human hand blindly into Swift nesting holes, nestlings were stimulated to beg and to grasp the approaching fingers. The results show that the smallest nestlings in the nest were the first to encounter the approaching fingers. Small nestlings were also just as likely to be found with at least some food in their crops as were medium and large nestlings, but gained mass at a significantly slower rate. I suggest that parent Swifts can easily access small nestlings, but prefer either to allocate more food to larger nestlings or to allow sibling competition in order to facilitate brood reduction.

Lotem A. 1998. Higher levels of begging behavior by small nestlings: a case of a negatively correlated handicap. Israel J. of Zool. 44:29-45. (PDF version)

Abstract: Recent theoretical models of parent-offspring conflict suggest that costly solicitation by offspring reflects offspring need in a reliable manner, and that parents are, therefore, selected to increase parental effort in response to offspring solicitation. However, theory and experiments suggest that parents pay attention not only to their nestlings' needs, but also to their relative quality as reflected by size and competitive ability. A study on barn swallow nestlings, described here, investigates how such complex feeding rules affect nestling begging strategies, and how different begging strategies affect the nestlings' relative success. Begging strategies were compared for large and small brood mates, assumed to represent high and low nestling qualities, respectively. The results indicate that small nestlings tend to beg at greater intensities than large nestlings for a similar level of food deprivation. A-higher intensity of begging does not, however, guarantee greater success for smaller nestlings because mass gain by nestlings is affected by both size and begging differences among the competing nestlings. I suggest that higher levels of begging by small nestlings are caused by differences in the expected benefit for a given level of begging, and create a negative correlation between the optimal level of signaling and the signaler's quality. This contrasts with the typical handicap case discussed in the literature, in which differences among individuals in the cost of signaling create a positive correlation between the optimal level of signaling and the signaler's quality. This study suggests that "negatively correlated handicaps" may emerge whenever receivers integrate cryptic information about the signaler's momentary need or motivation, based on one signal, and non-cryptic information about the signaler's quality based on other cues.

Balshine-Earn S., Lotem A. 1998. Experimental evidence for individual recognition from video playbacks in a cooperatively breeding cichlid (Neolamprologus brichardi). Behaviour 135:1-18  PDF VERSION

Abstract: Most theories of social behaviour and cooperation assume that animals can recognise other individuals, but this is rarely tested. Using Neolamprologus brichardi, a cooperatively breeding cichlid fish, we monitored behavioural responses to (1) real fish versus video images of fish; (2) mate versus neighbour and (3) video images of mate versus video image of neighbour. All tests were controlled for size and sex. Fish reacted appropriately to the playbacks, although responses to videos were not as strong as to real fish. Both males and females fought against the images of stranger and neighbour fish and they courted images of mates. These results confirm that the cooperatively breeding fish, Neolamprologus brichardi, recognises individuals based on vision and that video playbacks contain sufficient information to facilitate recognition.

Rodriguez-Gironez M., Lotem A. 1998. Acceptance by the splendid fairy-wren of parasitism by Horsfield's bronze-cuckoo: re-examination of Brooker and Brooker equilibrium model. Behavioral Ecology 9:419-420. PDF VERSION

Abstract: Brooker and Brooker (1996) have recently published data from a 17 year study of a splendid fairy-wren (Malurus splendens) population parasitized by Horsfield's bronze-cuckoo (Chrysococcyx basalis) in Western Australia. They argue that "of the two explanations for the lack of rejection, neither really stands up to scrutiny with respect to the splendid fairy-wren" (p. 396). Instead, they propose a new model for evolutionary equilibrium based on the life history and population structure of the host species. According to their model, pure acceptance of parasitic eggs and chicks is an evolutionarily stable strategy (ESS, Maynard Smith and Price, 1973) regardless of how costly rejection of parasitic eggs might be. While we endorse the use of equilibrium models in the study of avian brood parasitism, we find some problems in the specific model proposed by Brooker and Brooker. Namely, we suspect that their model cannot be stable.

Lotem A., & Nakamura H., 1998. Evolutionary equilibria in Avian brood parasitism: an alternative for the "arms race-evolutionary lag" concept. In Parasitic birds and their hosts: studies in coevolution. Ed. by S.I. Rothstein and S.K. Robinson, pp. 223-235. Oxford University Press. Oxford.

Abstract: Based on a review of the literature, this paper investigates whether avian brood parasitism systems are continuously coevolving as in an arms race, or rather they are in an evolutionary equilibrium. Under the "arms race" view, the acceptance of parasitic eggs or nestlings, which reduces host fitness, is a result of an evolutionary lag in the development of counter adaptations by the host.. Under the equilibrium view, acceptance is an inevitable result of an equilibrium among various selective pressures. The possible costs and benefits of egg rejection are summarized in a model, and some possible ways in which an equilibrium might be expressed in a host population are suggested. Available data on avian brood parasitism are discussed in relation to the equilibrium hypothesis; Direct measurements of rejection costs and benefits rarely provide conclusive results but suggest that in many systems an equilibrium is as reasonable an interpretation as evolutionary lag. Evidence for adaptive rules in the occurrence of rejections and acceptances within a host population provides the strongest support for the equilibrium model. Comparative evidence previously explained by the arms race model, is shown here to fit the equilibrium model as well.

Lotem A. & Rothstein S.I. 1995. Cuckoo-host coevolution: from snapshots of an arms race to the documentation of microevolution. Trends in Ecology and Evolution 10:436-437. (PDF version)

Abstract: It is not often that a notable study in evolutionary biology published in Nature has nearly all of its assumptions and conclusions challenged by a second paper. But this is precisely what happened when Zuniga and Redondo1 questioned Soler and Moller's2 work on coevolution between the brood parasitic great spotted cuckoo (Clamator glandarius) and its magpie (Pica pica) host.

Lotem A., Nakamura H. & A. Zahavi. 1995. Constraints on egg discrimination and cuckoo-host coevolution. Anim. Behav. 49:1185-1209. (PDF version)

Abstract: To understand the co-existence of rejection and acceptance of cuckoo eggs within a host population, the mechanism of egg discrimination and the cost-benefit balance of rejection behaviour were investigated. At a study site in central Japan, rejection rate of cuckoo, Cuculus canorus, eggs by great reed warblers, Acrocephalus arundinaceus, was 61·5%. An analysis of host response to natural and experimental parasitism with real cuckoo eggs, cuckoo egg models and painted host eggs indicated that: (1) hosts are more likely to reject eggs that look different from their own; (2) almost all individuals (94%) can reject highly non-mimetic eggs, suggesting that there are few, if any, true accepter genotypes in the host population; (3) hosts usually reject by egg ejection; (4) during the host-laying period, the day of parasitism does not affect host response; (5) egg types that were rejected at lower rates also took longer to be rejected; (6) acceptance was more likely to occur among mid-season breeders which consist of a higher proportion of younger females in the host population. Two experiments indicated that previous exposure of a host to its own eggs affects its rejection behaviour, suggesting that a learning mechanism (an imprinting-like process) is involved. Parasitized nests from which the cuckoo egg was experimentally removed, or ejected by hosts, fledged more host young than nests in which the cuckoo egg was accepted. Hosts that deserted parasitized nests were likely to re-nest, and the success of re-nests was high. Costs due to breakage of host eggs occurred in only 3·5% of successful cuckoo egg ejections. A cost-benefit model of egg rejection suggests that under some circumstances, the cost of recognition errors may exceed that of parasitism. Egg variability within a clutch was higher among younger females. Some hosts rejected painted eggs and conspecific eggs based on differences that may occur naturally within variable clutches of other individuals. It is suggested that host egg variability is a major constraint on the learning mechanism of egg recognition. Accordingly, the cost of mistakenly rejecting an odd egg from the nest selects for greater tolerance towards divergent eggs in young breeders, and justifies a prolonged learning mechanism in which a host can learn to recognize the variation range of its own eggs. The co-existence of rejection and acceptance within the host population can therefore be explained as a compromise between the cost of parasitism and the cost of recognition errors, rather than as an evolutionary lag. This explanation is particularly pertinent where the cuckoo has evolved mimetic eggs and where the parasitism rate is low.

Lotem A. 1993. Secondary sexual ornaments as signals: the handicap approach and three possible problems. Ethologia 3:209-218. Proceedings of the XXIII International Ethological Conference, Torremolinos, Spain (An invited plenary lecture). (PDF version)

Abstract: Secondary sexual ornaments have recently been discussed in the context of biological signals, and the handicap principle has been suggested as a model explaining their evolution. The handicap principle predicts that at equilibrium, sexual ornaments will be honest signals of the male's quality. This is because the cost of ornaments to a potential cheater (a low quality male) will be greater than to an honest signaler (a high quality male), to an extent that makes cheating maladaptive. Accordingly, the cost of the ornament (the handicap) should be related to the quality it reveals. In the following, I discuss three problems with the handicap approach: i) It is difficult to determine the cost of the handicap and the quality it reveals. Nevertheless, I suggest that it is feasible and is worth doing. ii) It is not clear whether phylogenetic data can be used to distinguish between the handicap model and the sensory exploitation model. I suggest that it can be used only under restricted conditions. iii) Cheating (dishonest signalling) seems to contradict the handicap model. I will try to show, however, that some forms of cheating can be explained by the handicap model.

Lotem A. 1993. Learning to recognize nestlings is maladaptive for cuckoo Cuculus canorus host. Nature 362:743-745. (PDF version)

Abstract: The picture of a tiny passerine host feeding a huge cuckoo nestling challenges evolutionary biologists who explain animal behaviour as adaptive(1-4). Cuckoo eggs sometimes resemble the eggs of the host, but nestlings of the common cuckoo, Cuculus canorus, look very different from the young of the host. The inability of the host to discriminate against such divergent nestlings is especially puzzling as some cuckoo hosts show a finely tuned discrimination ability between eggs(5-8). Here I present a simple model to explain this paradox. The model shows that although learning to recognize eggs is adaptive, learning to recognize nestlings might not be. The mechanism of learned recognition, previously shown to maintain egg recognition, is unlikely to be adaptive for hosts like those of the common cuckoo, in which only the parasitic nestling remains in the nest. The reason that discrimination against parasite nestlings is not adaptive is that the cost of misimprinting (learning to recognize the parasite nestling as the parents' own) exceeds the benefit of correct learning. The model also explains why nestling discrimination is mostly found in host-parasite systems in which the parasite and the hosts' young are reared together(1).

Lotem A., Nakamura H. & A. Zahavi. 1992. Rejection of cuckoo eggs in relation to host age: a possible evolutionary equilibrium. Behavioral Ecology 3:128-132. PDF VERSION

Abstract: Because hosts that accept a parasitic egg laid by the common cuckoo, Cuculus canorus, are unlikely to fledge their own offspring, rejection should be an adaptive response. Evidence that cuckoo host species attain only intermediate rates of rejection are commonly interpreted as resulting from an evolutionary lag. Yet, we found that the acceptance of cuckoo eggs by female great reed warblers, Acrocephalus arundinaceus, occurs mainly among the younger breeders in the host population. We suggest that some level of acceptance can arise in the host population as a result of the need of naive breeders to learn to reliably recognize their own eggs rather than representing evolutionary lag.

Lotem A., Schechtman E. & G. Katzir. 1991. Little egrets' Egretta garzetta capture of submerged prey: Strike depth, strike angle and possible effects of light refraction. Anim. Behav. 42:341-346. PDF VERSION

Abstract: How little egrets catch submerged prey was observed in the field. The proportion of successful strikes was measured relative to the angle and depth of the strike and the water level in the pond. Prey capture success was significantly related to strike angle, being highest at the most acute angles. Strike depth had no effect on capture success. Strikes were more successful in shallow streams than in full or partly drained ponds. Adult breeding birds were as successful as non-breeders and juveniles, but performed deeper strikes more often. There was also significant variation between individuals in capture success. Light refraction had no apparent effect on the egrets' capture success.

Katzir, G., Lotem, A. & N. Intrator. 1989. Stationary underwater prey missed by reef herons, Egretta gularis: head position and light refraction at the moment of strike. J. Comp. Physiol. A. 165:573-576. PDF VERSION

Abstract: This paper attempts to verify the importance of spatial positioning of the eyes of reef herons Egretta gularis schistacea, when coping with light refraction at the air-water interface. The herons' striking of prey, while their approach angle was restricted, was observed. (a) The herons' capture success in the restricted situation was markedly lower than in the unrestricted situation. (b) The points of strike (STR) in unsuccessful strikes differed from those of successful strikes, and from those of the unrestricted situation. (c) The larger the differences between the observed and the predicted ratio of prey depth to apparent prey depth, the higher the probability of missing a prey. These results support predictions of a model presented elsewhere (Katzir and Intrator 1987) that a heron will attempt to reach spatial positions at which prey's real depth and apparent depth are linearly correlated.




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