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Song length and ‘male quality’ in the chiffchaff
606
Animal Behaviour, 36, 2
Yasukawa, K. & Searcy, W. A. 1982. Aggressiveness in female red-winged blackbirds: a strategy to ensure male parental investment. Behav. Ecol. Sociobiol., l 1, 13-17.
(Received 11 July 1987; revised 25 September 1987; MS. number: sc-386)
Song Length and 'Male Quality' in the Chiffchaff A measure of song length has recently been proposed as an important aspect of song variation. Lambrechts & D h o n d t (1986, 1987) have suggested that 'strophe length', the number o f repetitions of the elements making up a song in great tits, Parus major, is a signal o f male quality. They found significant differences between males in this measure of song length during spontaneous song, and correlations between song length, dominance at a winter feeding site and a measure of reproductive success (Lambrechts & D h o n d t 1986). They suggest that song length reflects a male's singing capacity and consequently gives information about 'strength' and/or 'male quality' (Lambrechts & D h o n d t 1987). The present study investigates song length in chiffchaffs, Phylloscopus collybita, during spontaneous song and in response to a territorial intrusion simulated by song playback. The role of song length in signalling male quality in great tits is complicated by each male having a repertoire of song types (McGregor & Krebs 1982) since most song types have different lengths of repeated unit. This problem does not arise with chiffchaff song as there are no recognizable song types: song consists of up to four different elements which are not alternated in the stereotyped manner of great tit song. Song length can be taken as the number of elements of all types in each song, e.g. 'chiff chaff chiff chaff' would be considered equivalent to 'chaff chaff chiff chaff': both have a song length of four. There is little variation within and between males in the duration of elements (Schubert 1971) and the gap between them (personal observation), therefore the 'number of elements' measure of song length is closely correlated with the actual duration of songs, The study took place from 6 to 18 April 1987 in Woodchester Park, Gloucestershire. A b o u t 60 songs (,('+ SE= 59.3 + 4'9) of spontaneous song were recorded from each o f 11 territorial male chiffchaffs from a distance of less than 15 m between 0800 and 1100 hours on 14 and 15 April. Song was recorded with a U h e r 4000 Report Monitor (Agfa P E M 369 tape at 19 cm/s) and a Sennheiser M K H 816T directional microphone with Audio Engineering AKB-11 preamplifier (2
kHz high pass filter enabled). Song length was counted from these recordings played at 9.5 cm/s. Modal song length was 10, the means of individual males ranged from 12.6 to 7.5, the maximum song length recorded was 34 and the minimum 1. Males' song lengths were approximately normally distributed; only one of the 11 frequency distributions differed significantly from normal. There was significant between-male variation in song length (one-way A N O V A , F10,619 -~ 6"91, P < 0.0001). This result is not just a reflection o f the large sample size involved; if only the first 10 songs recorded from each male are used, the result is comparable (F10,99 = 2"92, P < 0"001). A singing territorial intruder was simulated by song playback for 2 min. Nine males were played a tape consisting of a 10-element song (lasting 3.3 s) repeated 6 times/rain. A Sony T C D - 5 P r o cassette recorder played a T D K 20 s endless cassette loop and song was broadcast by a Nagra D S M speaker/ amplifier. The playback song was recorded from a territorial male at least two territories distant from all experimental males. The speaker/amplifier was placed 2-3 m above the ground in a small tree about 20 m inside the territory boundary o f the experimental male facing into the territory. The Table I. Correlations between strength of response to playback,* song length and change in song length Change in Song length song length During playback Mean Maximum Minimum First
- 0.052 0.009 0.068 -0.094
0-1 0.008 0.42 -0-1
After playback Mean Maximum Minimum First
- 0.05 0.083 - 0.472 -0.251
- 0-05 0.05 0.306 -0.233
Values are rs, N=9, rs critical value at 5%, one-tailed = ___0.6. * The aggregate response score was produced by principal component analysis (BMDP4M) of the eight separate scores with the following loadings: latency, 0"184; latency to song, - 0.052; approach < 20 m latency, 0.588; closest approach, -0.571; time within 20 m, 0.718; time singing, 0.869; number of songs, 0"917; total time singing, calling, approaching or < 20 m, 0.968. This factor accounted for 48.1% of the variance.
Short Communications observer was 20 m from the speaker/amplifier and recorded all songs sung by the male for 2 min before, 2 min during and 6 min after playback using the Uher and Sennheiser. Information on approach, distance and displays was spoken onto the same tape. Eight measures of strength of response were obtained from the tape and principal component analysis was used to generate an aggregate score from these eight measures (see Huntingford 1976; McGregor & Avery 1986; and Table I for factor loadings). The response to playback was uniformly strong. Males first responded after about 30 s ()?__SE=30-33_ 13.07 S), sang for about 65% of the available time (307.44 + 36.44 s) and, with the exception of one male, approached to within 5 m of the speaker (6.73+4.19 m). Males sang at a significantly lower rate during playback (1.44+0.58 songs/min) than after playback (5.73___0.94 songs/min; P < 0.02, two-tailed Wilcoxon matched-pairs signed-ranks test). If song length indicates male strength or quality to rivals during aggressive encounters, we would expect the simulation of a territorial intrusion by playback to elicit longer songs. Since males are known to differ in spontaneous song length, change in song length was calculated by subtracting the corresponding pre-playback value for each male. An exception was change in first song length, where pre-playback mean song length was subtracted. Contrary to predictions, songs were shorter during playback. Maximum song length and length of first song significantly decreased ( - 7"56___3-48 and - 4 . 1 8 + 1 - 2 respectively); mean and minimum song length showed the same trend ( - 3 . 4 + 1.73 and - 1.44-1- 1.8; Wilcoxon test, two-tailed, N = 9 , P<0"01, P<0.02, P=0.1 and NS respectively). A similar decrease in song length during playback has also been found in willow warblers (Phylloscopus trochilus; Jarvi et al. 1980) and great reed warblers (Acrocephalus arundinaceus; Catchpole 1983). The effect of playback on song length after playback was not so clear; mean and maximum song lengths tended to increase (0.28 -¢-0.89 and 8.22 4- 4.46), the length of the first song tended to decrease ( - 0 . 5 1 4- 1.83) and minimum song length significantly decreased (-3"56+0.65; Wilcoxon test, two-tailed, N = 9 , P < 0-01). Therefore, the results from three species show that playback tends to elicit shorter, rather than longer, songs. If differences in song length indicate differences in the strength with which males can respond to rival males, we might expect changes in song length to be positively correlated with strength of response to playback. Eight measures of change in song length (mean, maximum, minimum and length of
607
first song, both during and after playback) were correlated with the eight separate strength-ofresponse measures. Two of the resulting 64 correlations (one negative, one positive) were significant, fewer than the number expected to occur by chance with a 5%, two-tailed significance criterion. Table I shows correlations between the principal component aggregate measure and eight measures of song length and change in song length; none is significant. Therefore, there does not seem to be any tendency for differences between males in strength of response to playback to be reflected in song length measures. The frequency distributions of song length before and after playback were also compared for each male; two males showed a significant difference in distributions (Kolmogorov-Smirnov twosample test, ~2=25.8, df=2, P<0.001 and 13.7, P < 0.0025), both differences were caused by more frequent use of longer songs. These males showed no other obvious differences in song length or strength-of-response measures. To investigate male differences further, the nine experimental males were divided into two groups according to whether the mean song length in the pre-playback period was less (N--- 5) or greater (N--- 4) than that used for playback (10). No significant differences or consistent trends were found when the two groups were compared for any of the nine strength-of-response measures or eight song length measures. Following Lambrechts & Dhondt (1987), the two males with the longest, and one male with the shortest, preplayback mean song lengths were examined in detail. The males with the longest songs before playback tended to decrease mean and maximum song length after playback whereas the other male increased, the opposite of Lambrechts & Dhondt's (1987) result. None of these differences was significant and other males showed greater increases and decreases. Overall these results show that male chiffchaffs differ significantly in the song length used in spontaneous singing but there is no obvious effect of playback on song length apart from a decrease during playback. Detailed analysis of each male's response to playback gives no support for the idea that spontaneous song length predicts ability to change song length in response to playback. Given that this study was able to exclude the complicating factor of song types, it seems unlikely that song length is a simple indicator of male quality or strength in this species and calls into question the general applicability of Lambrechts & Dhondt's (1986, 1987) hypothesis. I thank Mr. A. R. Kelly for access to the study site, the Nuffield Foundation and SERC for finan-
608
Animal Behaviour, 36, 2
cial support, Leonie McGregor for help with analyses, and two referees and the European editor for helpful comments. P. K. MCGREGOR Department o f Zoology, University o f Nottingham, University Park, Nottingham NG7 2RD, U.K.
References Catchpole, C. K. 1983. Variation in the song of the great reed warbler Acrocephalus arundinaeeus in relation to mate attraction and territory defence. Anita. Behav., 31, 1217-1225. Huntingford, F. A. 1976. An investigation of the territorial behaviours of the 3-spinedstickleback (Gasterosteus aculeatus) using principal component analysis. Anon. Behav., 24, 822-834. Jarvi, T., Rades/iter,T. & Jakobsson, S. 1980.The song of the willow warbler Phylloscopus trochilus with special reference to singing behaviour in agonistic situations. Ornis Scand., 11, 236-242. Lambrechts, M. & Dhondt, A. A. 1986. Male quality, reproduction and survival in the great tit (Parusmajor). Behav. Ecol. Sociobiol., 19, 57~i3. Lambrechts, M. & Dhondt, A. A. 1987. Differences in singingperformance betweenmale great tits. Ardea, 75, 43-52. McGregor, P. K. & Avery, M. I. 1986. The unsung songs of great tits (Parus major): learning neighbours' songs for discrimination. Behav. Ecol. Sociobiol., 18, 311316. McGregor, P. K. & Krebs, J. R. 1982. Song types in a population of great tits: their distribution, abundance and acquisition by individuals. Behaviour,52, 126-152. Schubert, G. 1971. ExperimentelleUntersuchungen iiber die artkennzeichnenden Parameter im Gesang des Zilpzalps (Phylloscopus c. collybita) (Vieillot). Behaviour, 38, 289-314. (Received 22 August 1987; revised 5 October 1987; MS. number: sc-391)
Male Investment Time and Mating Decisions in Amphipods: Uncertainty or Deprivation? Dunham et al. (1986) repeated the investigation of mate guarding decisions in the estuarine amphipod Gammarus lawrencianus, previously studied by Hunte et al. (1985). In the latter paper, we used the time that a male would endure osmotic stress before releasing a female from amplexus (male tenacity index) as an index of male assessment of female value. We found that (1) females are valued more highly the closer they are to copulation (subsequently referred to as female state) and (2) females of a given state are valued more highly the longer the male has amplexed with the female (i.e. the greater his past investment in amplexus). We
suggested that the latter occurs because: (1) males are uncertain of the true reproductive state of a female on first contact, (2) the prior distribution of unamplexed females likely to be encountered by males causes them initially to undervalue the reproductive state of females, and (3) time spent amplexing allows information to be gathered which reduces the male's uncertainty of female state. In short, we suggested that males of G. lawrencianus are Bayesian decision-makers. We call this explanation the uncertainty hypothesis. Rather than using a tenacity index, Dunham et al. separated amplexed pairs and used the probability of re-amplexing over a 3-min period as an indication of male assessment of female value. Their experimental design improved on ours in that (1) it allowed separation of female reproductive state from time invested in amplexus by females (female investment time) as factors influencing the probability of re-amplexus, and (2) it used strange females in re-amplexus experiments thereby ensuring that individual recognition could not affect the results. Note, however, that if the decision of whether to amplex or whether to release a female under osmotic stress is made by the male (as may be the case over a range of male-size/female-size combinations; Hunte et al. 1985), it may not be affected by female investment time. Note, also, the conclusion of Dunham et al. that individual recognition is not involved in mate guarding decisions in G. lawrencianus. Dunham et al. found that re-amplexus was more likely the closer the female was to copulation (consistent with our results), and claimed that the amount of time invested by males in amplexus (male investment time) increased the probability of re-amplexus (consistent with our results). They suggest that the latter observation is better explained by males valuing females more highly as the amount of time since the male's previous copulation increases. We call this explanation the deprivation hypothesis. Our intention here is to show that, contrary to the claim of Dunham et al., (1) their data do not suggest that the amount of time since the last copulation significantlyincreases the probability of males re-amplexing, (2) the deprivation hypothesis cannot explain our observation that females of a given state are valued more highly the longer the male has amplexed with the female, and (3) both their data and ours are more consistent with the uncertainty hypothesis than with the deprivation hypothesis. In experiment 2 in Dunham et al., males and females on their first day of amplexus (M0 males and F0 females) were separated and isolated for 3 min. Each M0 male was then tested against a strange F0 female to determine whether amplexus
Animal Behaviour, 36, 2
Yasukawa, K. & Searcy, W. A. 1982. Aggressiveness in female red-winged blackbirds: a strategy to ensure male parental investment. Behav. Ecol. Sociobiol., l 1, 13-17.
(Received 11 July 1987; revised 25 September 1987; MS. number: sc-386)
Song Length and 'Male Quality' in the Chiffchaff A measure of song length has recently been proposed as an important aspect of song variation. Lambrechts & D h o n d t (1986, 1987) have suggested that 'strophe length', the number o f repetitions of the elements making up a song in great tits, Parus major, is a signal o f male quality. They found significant differences between males in this measure of song length during spontaneous song, and correlations between song length, dominance at a winter feeding site and a measure of reproductive success (Lambrechts & D h o n d t 1986). They suggest that song length reflects a male's singing capacity and consequently gives information about 'strength' and/or 'male quality' (Lambrechts & D h o n d t 1987). The present study investigates song length in chiffchaffs, Phylloscopus collybita, during spontaneous song and in response to a territorial intrusion simulated by song playback. The role of song length in signalling male quality in great tits is complicated by each male having a repertoire of song types (McGregor & Krebs 1982) since most song types have different lengths of repeated unit. This problem does not arise with chiffchaff song as there are no recognizable song types: song consists of up to four different elements which are not alternated in the stereotyped manner of great tit song. Song length can be taken as the number of elements of all types in each song, e.g. 'chiff chaff chiff chaff' would be considered equivalent to 'chaff chaff chiff chaff': both have a song length of four. There is little variation within and between males in the duration of elements (Schubert 1971) and the gap between them (personal observation), therefore the 'number of elements' measure of song length is closely correlated with the actual duration of songs, The study took place from 6 to 18 April 1987 in Woodchester Park, Gloucestershire. A b o u t 60 songs (,('+ SE= 59.3 + 4'9) of spontaneous song were recorded from each o f 11 territorial male chiffchaffs from a distance of less than 15 m between 0800 and 1100 hours on 14 and 15 April. Song was recorded with a U h e r 4000 Report Monitor (Agfa P E M 369 tape at 19 cm/s) and a Sennheiser M K H 816T directional microphone with Audio Engineering AKB-11 preamplifier (2
kHz high pass filter enabled). Song length was counted from these recordings played at 9.5 cm/s. Modal song length was 10, the means of individual males ranged from 12.6 to 7.5, the maximum song length recorded was 34 and the minimum 1. Males' song lengths were approximately normally distributed; only one of the 11 frequency distributions differed significantly from normal. There was significant between-male variation in song length (one-way A N O V A , F10,619 -~ 6"91, P < 0.0001). This result is not just a reflection o f the large sample size involved; if only the first 10 songs recorded from each male are used, the result is comparable (F10,99 = 2"92, P < 0"001). A singing territorial intruder was simulated by song playback for 2 min. Nine males were played a tape consisting of a 10-element song (lasting 3.3 s) repeated 6 times/rain. A Sony T C D - 5 P r o cassette recorder played a T D K 20 s endless cassette loop and song was broadcast by a Nagra D S M speaker/ amplifier. The playback song was recorded from a territorial male at least two territories distant from all experimental males. The speaker/amplifier was placed 2-3 m above the ground in a small tree about 20 m inside the territory boundary o f the experimental male facing into the territory. The Table I. Correlations between strength of response to playback,* song length and change in song length Change in Song length song length During playback Mean Maximum Minimum First
- 0.052 0.009 0.068 -0.094
0-1 0.008 0.42 -0-1
After playback Mean Maximum Minimum First
- 0.05 0.083 - 0.472 -0.251
- 0-05 0.05 0.306 -0.233
Values are rs, N=9, rs critical value at 5%, one-tailed = ___0.6. * The aggregate response score was produced by principal component analysis (BMDP4M) of the eight separate scores with the following loadings: latency, 0"184; latency to song, - 0.052; approach < 20 m latency, 0.588; closest approach, -0.571; time within 20 m, 0.718; time singing, 0.869; number of songs, 0"917; total time singing, calling, approaching or < 20 m, 0.968. This factor accounted for 48.1% of the variance.
Short Communications observer was 20 m from the speaker/amplifier and recorded all songs sung by the male for 2 min before, 2 min during and 6 min after playback using the Uher and Sennheiser. Information on approach, distance and displays was spoken onto the same tape. Eight measures of strength of response were obtained from the tape and principal component analysis was used to generate an aggregate score from these eight measures (see Huntingford 1976; McGregor & Avery 1986; and Table I for factor loadings). The response to playback was uniformly strong. Males first responded after about 30 s ()?__SE=30-33_ 13.07 S), sang for about 65% of the available time (307.44 + 36.44 s) and, with the exception of one male, approached to within 5 m of the speaker (6.73+4.19 m). Males sang at a significantly lower rate during playback (1.44+0.58 songs/min) than after playback (5.73___0.94 songs/min; P < 0.02, two-tailed Wilcoxon matched-pairs signed-ranks test). If song length indicates male strength or quality to rivals during aggressive encounters, we would expect the simulation of a territorial intrusion by playback to elicit longer songs. Since males are known to differ in spontaneous song length, change in song length was calculated by subtracting the corresponding pre-playback value for each male. An exception was change in first song length, where pre-playback mean song length was subtracted. Contrary to predictions, songs were shorter during playback. Maximum song length and length of first song significantly decreased ( - 7"56___3-48 and - 4 . 1 8 + 1 - 2 respectively); mean and minimum song length showed the same trend ( - 3 . 4 + 1.73 and - 1.44-1- 1.8; Wilcoxon test, two-tailed, N = 9 , P<0"01, P<0.02, P=0.1 and NS respectively). A similar decrease in song length during playback has also been found in willow warblers (Phylloscopus trochilus; Jarvi et al. 1980) and great reed warblers (Acrocephalus arundinaceus; Catchpole 1983). The effect of playback on song length after playback was not so clear; mean and maximum song lengths tended to increase (0.28 -¢-0.89 and 8.22 4- 4.46), the length of the first song tended to decrease ( - 0 . 5 1 4- 1.83) and minimum song length significantly decreased (-3"56+0.65; Wilcoxon test, two-tailed, N = 9 , P < 0-01). Therefore, the results from three species show that playback tends to elicit shorter, rather than longer, songs. If differences in song length indicate differences in the strength with which males can respond to rival males, we might expect changes in song length to be positively correlated with strength of response to playback. Eight measures of change in song length (mean, maximum, minimum and length of
607
first song, both during and after playback) were correlated with the eight separate strength-ofresponse measures. Two of the resulting 64 correlations (one negative, one positive) were significant, fewer than the number expected to occur by chance with a 5%, two-tailed significance criterion. Table I shows correlations between the principal component aggregate measure and eight measures of song length and change in song length; none is significant. Therefore, there does not seem to be any tendency for differences between males in strength of response to playback to be reflected in song length measures. The frequency distributions of song length before and after playback were also compared for each male; two males showed a significant difference in distributions (Kolmogorov-Smirnov twosample test, ~2=25.8, df=2, P<0.001 and 13.7, P < 0.0025), both differences were caused by more frequent use of longer songs. These males showed no other obvious differences in song length or strength-of-response measures. To investigate male differences further, the nine experimental males were divided into two groups according to whether the mean song length in the pre-playback period was less (N--- 5) or greater (N--- 4) than that used for playback (10). No significant differences or consistent trends were found when the two groups were compared for any of the nine strength-of-response measures or eight song length measures. Following Lambrechts & Dhondt (1987), the two males with the longest, and one male with the shortest, preplayback mean song lengths were examined in detail. The males with the longest songs before playback tended to decrease mean and maximum song length after playback whereas the other male increased, the opposite of Lambrechts & Dhondt's (1987) result. None of these differences was significant and other males showed greater increases and decreases. Overall these results show that male chiffchaffs differ significantly in the song length used in spontaneous singing but there is no obvious effect of playback on song length apart from a decrease during playback. Detailed analysis of each male's response to playback gives no support for the idea that spontaneous song length predicts ability to change song length in response to playback. Given that this study was able to exclude the complicating factor of song types, it seems unlikely that song length is a simple indicator of male quality or strength in this species and calls into question the general applicability of Lambrechts & Dhondt's (1986, 1987) hypothesis. I thank Mr. A. R. Kelly for access to the study site, the Nuffield Foundation and SERC for finan-
608
Animal Behaviour, 36, 2
cial support, Leonie McGregor for help with analyses, and two referees and the European editor for helpful comments. P. K. MCGREGOR Department o f Zoology, University o f Nottingham, University Park, Nottingham NG7 2RD, U.K.
References Catchpole, C. K. 1983. Variation in the song of the great reed warbler Acrocephalus arundinaeeus in relation to mate attraction and territory defence. Anita. Behav., 31, 1217-1225. Huntingford, F. A. 1976. An investigation of the territorial behaviours of the 3-spinedstickleback (Gasterosteus aculeatus) using principal component analysis. Anon. Behav., 24, 822-834. Jarvi, T., Rades/iter,T. & Jakobsson, S. 1980.The song of the willow warbler Phylloscopus trochilus with special reference to singing behaviour in agonistic situations. Ornis Scand., 11, 236-242. Lambrechts, M. & Dhondt, A. A. 1986. Male quality, reproduction and survival in the great tit (Parusmajor). Behav. Ecol. Sociobiol., 19, 57~i3. Lambrechts, M. & Dhondt, A. A. 1987. Differences in singingperformance betweenmale great tits. Ardea, 75, 43-52. McGregor, P. K. & Avery, M. I. 1986. The unsung songs of great tits (Parus major): learning neighbours' songs for discrimination. Behav. Ecol. Sociobiol., 18, 311316. McGregor, P. K. & Krebs, J. R. 1982. Song types in a population of great tits: their distribution, abundance and acquisition by individuals. Behaviour,52, 126-152. Schubert, G. 1971. ExperimentelleUntersuchungen iiber die artkennzeichnenden Parameter im Gesang des Zilpzalps (Phylloscopus c. collybita) (Vieillot). Behaviour, 38, 289-314. (Received 22 August 1987; revised 5 October 1987; MS. number: sc-391)
Male Investment Time and Mating Decisions in Amphipods: Uncertainty or Deprivation? Dunham et al. (1986) repeated the investigation of mate guarding decisions in the estuarine amphipod Gammarus lawrencianus, previously studied by Hunte et al. (1985). In the latter paper, we used the time that a male would endure osmotic stress before releasing a female from amplexus (male tenacity index) as an index of male assessment of female value. We found that (1) females are valued more highly the closer they are to copulation (subsequently referred to as female state) and (2) females of a given state are valued more highly the longer the male has amplexed with the female (i.e. the greater his past investment in amplexus). We
suggested that the latter occurs because: (1) males are uncertain of the true reproductive state of a female on first contact, (2) the prior distribution of unamplexed females likely to be encountered by males causes them initially to undervalue the reproductive state of females, and (3) time spent amplexing allows information to be gathered which reduces the male's uncertainty of female state. In short, we suggested that males of G. lawrencianus are Bayesian decision-makers. We call this explanation the uncertainty hypothesis. Rather than using a tenacity index, Dunham et al. separated amplexed pairs and used the probability of re-amplexing over a 3-min period as an indication of male assessment of female value. Their experimental design improved on ours in that (1) it allowed separation of female reproductive state from time invested in amplexus by females (female investment time) as factors influencing the probability of re-amplexus, and (2) it used strange females in re-amplexus experiments thereby ensuring that individual recognition could not affect the results. Note, however, that if the decision of whether to amplex or whether to release a female under osmotic stress is made by the male (as may be the case over a range of male-size/female-size combinations; Hunte et al. 1985), it may not be affected by female investment time. Note, also, the conclusion of Dunham et al. that individual recognition is not involved in mate guarding decisions in G. lawrencianus. Dunham et al. found that re-amplexus was more likely the closer the female was to copulation (consistent with our results), and claimed that the amount of time invested by males in amplexus (male investment time) increased the probability of re-amplexus (consistent with our results). They suggest that the latter observation is better explained by males valuing females more highly as the amount of time since the male's previous copulation increases. We call this explanation the deprivation hypothesis. Our intention here is to show that, contrary to the claim of Dunham et al., (1) their data do not suggest that the amount of time since the last copulation significantlyincreases the probability of males re-amplexing, (2) the deprivation hypothesis cannot explain our observation that females of a given state are valued more highly the longer the male has amplexed with the female, and (3) both their data and ours are more consistent with the uncertainty hypothesis than with the deprivation hypothesis. In experiment 2 in Dunham et al., males and females on their first day of amplexus (M0 males and F0 females) were separated and isolated for 3 min. Each M0 male was then tested against a strange F0 female to determine whether amplexus