Parental Investment by the Northern Mockingbird: Male and Female Roles in Feeding Nestlings

PARENTAL INVESTMENT BY THE NORTHERN MOCKINGBIRD: MALE AND FEMALE ROLES IN FEEDING NESTLINGS

RANDALL BREITWISCH,PETER G. MERRITT, AND GEORGE H. WHITESIDES Departmentof Biology,University of Miami, CoralGables, Florida 33124 USA

ABSTRACT.--Analysisof 3,293 feeding trips to nestling Northern Mockingbirds(Mimus polyglottos)in the first11 daysof nestlinglife showedthat malesand femalesfed youngat similar rates.Young were fed a mixed diet of animal prey and fruits, and malesand females fed similarvolumes of animal prey and of fruits.Females displayed a monotonicincrease in feedingrate during nestlinglife but did not significantlyincrease load size.Males signifi- cantlyincreased both feedingrate and loadsize with ageof nestlings,and their feedingrate peakedin the mid-nestlingperiod, when younggrow mostrapidly. Males and femalesfed broodsof two and three young at similar rates.There was a biasedbreeding-adult sex ratio in this population,with malesoutnumbering females. The unbalancedsex ratio may allow femalesto demanda high level of male parentalcare in feeding nestlingsand in other behaviorsincluded in parentalinvestment. Received 19 April 1985,accepted 10 September 1985.

PARENTALinvestment (PI) is defined as "any nestlingsin proportionsthat maximize genetic investment by the parent in an individual off- contributionsto succeedinggenerations (Fish- springthat increasesthe offspring'schances of er 1958). We attempted to assessthe relative surviving (and hence reproductive success)at contributionsby malesand femalesto feeding the costof the parent'sability to invest in other nestlings;to establishif the patternsof feeding offspring" (Trivers 1972). When offspring are by malesand femaleswere similar, both daily typically aggregated in clutches, some compo- and throughout the nestling period; to find if nents of PI (e.g. nest defense)may be viewed the quality of food brought to nestlings by as a compromiseamong clutches separated in males and females was similar; and to see if time and spacerather than among individual there was a relationship between brood size offspring (Wittenberger 1981:362-363). Paren- and relative investment by males and females tal care (PC) is the nongametic subset of PI in feeding nestlings.In light of the limited the- comprisingthose behaviors involved in raising ory related to these questions,we submit our young to independence. empirical findings and interpretation as a par- In many monogamous bird species, both tial basisfor future development of theory re- males and females invest substantial amounts garding apportionment of parental invest- of time and energy in offspring,particularly in ments by males and females. feeding nestlingsand fledglings.In many mo- nogamouspassetines, males and females make STUDY AREA AND METHODS roughly equal numbers of food deliveries to This study was conductedon individually color- nestlings(Kendeigh 1952, Lack 1968,Emlen and bandedNorthern Mockingbirdsinhabiting the main Oring 1977, Oring 1982, Greenberg and Grad- campusof the University of Miami, Dade Co., Florida wohl 1983).However, the scheduleof feeding (Merritt 1985).We observedparental provisioning of nestlingsand the amountsfed by the sexessel- nestlings during 25 12-h periods (0600-1800) for a dom have been quantifiedrigorously. total of 300 h of observations.Data were gatheredon We studiedparental feeding of altricial nest- 12 broodsof 9 pairs of birds from 5 April to 9 July lings by Northern Mockingbirds(Mirnus poly- 1981 (23 of 25 periods between 1 May and 9 July). Fourbroods were observedfor one day each,4 broods glottos).Parental feeding of nestlingsis a major for two days, 3 broodsfor three days,and 1 brood time and energy investment in offspring(Rick- for four days.Broods sampled on two or more days lefs 1974, Skutch 1976, Breitwisch et al. 1984). were observedon nonconsecutivedays, with one ex- Therefore, selection should favor male and fe- ception (see Breitwisch et al. 1984). We observed 1 male distribution of investment in feeding brood when the young were six daysold (= day 6),

152 The Auk 103: 152-159. January 1986 January1986] MockingbirdParental Investment 153

3 broods at days 10 and 11, and 2 broods for each of ling life. Summing over the first 11 days of the nine remaining days (days 1-5, 7-9, 12). Mock- nestlinglife gave an estimateof the total vol- ingbirds in southern Florida fledge at about 12 days ume of animal food and fruit brought to a nest- of age. Broodsizes ranged from 1 to 4 (œ= 2.4, SD = ling by eachparent. Males and femalesdeliv- 0.79, n = 12). ered similar amounts of all foods combined Feeding trips to the nest were recordedto the near- est secondwith digital watches.Using binoculars,we during nestling life [males:1,518 (48.1%) vol- identified food itemsto majortype (e.g. fruit, insect, ume units, females: 1,640 (51.9%) volume units; spider, lizard), with finer levels of resolution when- Wilcoxonmatched-pairs signed-ranks test, T = ever possible(e.g. speciesof fruit or order of insect). 120, P >> 0.05, n = 23]. We estimatedlengths of animal prey (<¾i, ¾i-1, 1-2, Tripswith unknown foods.--In 511 feedingtrips 2-3, 3-4, 4-5, 5-6, 6-7, 7-8, >8 cm; size classes with (15.5%), unknown foods were delivered. Fe- lower limit closedand upper limit open). We esti- males made more trips delivering unknown mated relative volumes of foods on an arithmetic scale food items than males (323 vs. 188 trips; Wil- of 1-5; volume per centimeter was estimated for an- coxonmatched-pairs signed-ranks test, T = 52, imal prey. Volumesof all individual fruits were be- P < 0.05, n = 23). tween 1 and 5, inclusive, although parentsfrequent- ly brought more than one fruit in a single delivery. Day-to-dayfeeding patterns.--Both males and Volumes of all animal prey -<1 cm in length were females increased feeding rates as nestlings between 1 and 5, inclusive. Volumes of animal prey aged from day 1 to 11 (Spearman rank corre- > 1 cm in length were calculatedas (volume per cen- lation for males: r s= 0.518, for females: rs = timeter) x (length in centimeters).Daily mean load 0.693;both P's < 0.05, n's = 23) (Fig. 1). We di- sizes (• volume/trip) ranged from 2.51 to 6.85 for vided the nestling period into three parts (days animal prey and 3.11 to 6.50 for fruit trips. We cal- 1-4, 5-8, 9-11) in relation to the sigmoidal culated total volume of animals and fruits fed per growth pattern (Oniki and Merritt unpubL data) nesteach day and divided thesevalues by (12 x brood and comparedfeeding rates(by trip) by males size)to yield meanfood volume.nestling-•. h-•. Un- known foods were distributed between fruit and an- and females in each of these periods. No dif- imal categoriesbased on the proportions of known ferencewas significant,although in the mid- items fed by each parent. We assignedto unknown period, male predominancein feeding rate ap- foods the mean relative volumes of animals and fruits proachedsignificance [Wilcoxon matched-pairs fed by each parental sex to nestlingsat that age. signed-rankstests, T (days 1-4) = 12, P >> 0.05, n = 8; T (days 5-8) = 3, 0.10 > P > 0.05, n = 7; RESULTS T (days9-11) = 9, P >> 0.05, n = 8]. Total volumesof food delivered per nestling All feedingsby males and females.--Female by males and by femalesboth were correlated mockingbirdsmade 1,874feeding trips to nest- with nestling age (Table 1). We comparedfeed- lings (52.7%of total), and malesmade 1,680trips ing rates(by volume) by malesand femalesfor (47.3%)during the 12-daynestling period. Be- days 1-4, 5-8, and 9-11 (Wilcoxon matched- havior on day 12 departed from that on the pairs signed-rankstests). Females fed more previous 11 daysas one pair member (the male during days 1-4 (T = 4, P < 0.05, n = 8). Males in one pair, and the female in a secondpair) fed more during days 5-8, but the difference spent a large proportion of time nest building was not significant(T = 3, 0.10 > P > 0.05, n = instead of feeding nestlings. We therefore ex- 7). There was no difference in volumes fed dur- cluded data from day 12 from analyses.In the ing days 9-11 (T = 10, P >> 0.05, n = 8). first 11 daysof nestling life, femalesmade 1,724 In the latter part of the nestling period, fe- (52.4%) trips, and males made 1,569 (47.6%) malescontinued to increasefeeding rate; total trips. Feeding rates by the sexeswere similar volume of food.nestling-•.h-• delivered was (Wilcoxonmatched-pairs signed-ranks test, T = significantly correlatedwith nestling age for 122.5, P >> 0.05, n = 23). Estimates of the rel- days5-11 (r, = 0.567, P < 0.05, n = 15). During ativevolumes of foodbrought to nestlingsmay the sameperiod, male feeding rate (total food provide a greaterlevel of resolutionthan num- volume-nestling -• -h -•) decreasedsignificantly bersof trips (Royama1966, Wittenberger 1982, (r. = -0.509, P = 0.05, n = 15). referencesin Klomp 1970), but here yielded a Males increasedthe load size of animal trips similar conclusion. We calculated the mean to- as nestlingsaged, but females did not (Table tal volume of animal food and fruit delivered 1). Neither sexchanged load size for fruit trips per nestling by each sex for each day of nest- as nestlingsaged (Table 1). 154 ][•REITWISCH,MERRITT, AND WHITESIDES [Auk, Vol. 103

FemalesMalesßø • • s

0 • I 2 4 6 8 10 12 20 0(5.25) B 4- =16

o $ o

o o • o •2- o • ß o = 8 $ o oø ß o•.o •... o o

o o

0 110 I 112 Days after hatching Days after hatching

Fig. 1. Food delivery.nestling-•.h -• by male and female Northern Mockingbirds: (A) fruit trips, (B) animal trips, (C) fruit volume, (D) animal volume.

Females were responsible for 301 of 310 Both sexesbrought fruit in addition to ani- brooding bouts (97.1%), and frequency of mal prey to nestlings,and both fed more of brooding decreasedsharply from day 1 to 7, each type of food as nestlingsaged (Fig. 1, Ta- remaining low through day 12 (Breitwischet ble 1). A nonsignificant correlation between al. 1984). Although there was a strong inverse male animal trips and nestling age was offset relationship between frequency of brooding by malesbringing larger loadsof animal foods bouts by femalesand their feeding rate (rs= as nestlings aged. Males and females delivered -0.872, P < 0.05, n = 23), the correlation was similar volumes of animals and fruits to nest- confoundedby generallyincreasing energetic lings during nestling life (males: 1,320 animal demands of the nestlings during this period. volume units and 198 fruit volume units; fe- In addition, at the highest brooding frequen- males: 1,383 animal volume units and 257 fruit cies(days 1-4), femalesfed more than males. volume units) [Wilcoxonmatched-pairs signed- Feedingpatterns within days.--There was a ranks tests, T = 113 (animal volume), T = 89.5 negativecorrelation between hour of day (0600- (fruit volume), T = 120 (total volume), all P's >> 1800 = hours 1-12) and number of animal trips. 0.05, all n's = 23]. nestling-•.h -• by females (rs = -0.636, P < Parentalfeeding and brood size.--We compared 0.05,n = 12) but not by males(r, = -0.193, P >> feeding ratesby malesand femalesfor broods 0.05, n = 12). Both sexesdisplayed a positive of two (n = 10) and three young (n = 7). First, correlationbetween hour of day and number we tested the assumption that sampling of of fruit trips.nestling-•.h -• (rs = 0.723 for fe- broodsof two and three young was random males, r, = 0.699 for males, both P's < 0.05, n's = with respectto nestling age (randomization test, 12). P > 0.05). The daily feeding rates by males, Qualityof foodbrought to nestlings.--Mostan- females,and the sexestogether were compared imal prey containmuch higher percentagesof for broodsof two and three young. All tests protein than are containedby most fruits. Us- were nonsignificant[Kolmogorov-Smirnov two- ing this protein differenceas a rough measure sampletests (Siegel 1956), all P's > 0.05; Table of quality of food items, we comparedthe rel- 2]. There was a tendency, however, toward ative quality of foodsdelivered to nestlingsby smaller total volume of food-nestling-'.h -• males and females. delivered to larger broods. January1986] MockingbirdParental Investment 155

TABLE1. Correlationsbetween parental feeding rates TABLE2. Feeding rates by Northern Mockingbird or load sizes and nestling age in the Northern parentswith brood sizesof two and three young. Mockingbird.' Feeding ratea Parent Brood Brood Male Female Both Parent size = 2 size = 3 D b D ½ Trips. nestling-• .day-• Male 12.91 (5.603) 10.85 (4.066) 0.305 0.257 Animal 0.127 NS b 0.411 0.429 Female 12.61 (5.747) 12.00 (4.692) 0.266 0.229 Fruit 0.770 0.787 0.836 Both 25.52 (8.392) 22.85 (7.721) 0.285 0.229 Combined 0.518 0.693 0.675 aMean food volume.nestling-•.h -• (SD in paren- Volume. nestling-• .day-• theses). n = 10 for broods of two young; n = 7 for Animal 0.440 0.669 0.580 broodsof three young. Fruit 0.791 0.805 0.836 • Maximum deviation calculatedin the Kolmogo- Combined 0.549 0.754 0.696 rov-Smirnov two-sample test. All comparisonsnon- significant(P > 0.05). Cumulative distribution across Load size (mean relative volume/trip) days 1-11 after hatching. Animal 0.661 0.314 NS 0.534 cMaximum deviation calculatedin the Kolmogo- Fruit 0.197 NS 0.427 NS 0.330 NS rov-Smirnov two-sampletest. All comparisonsnon- Combined 0.658 0.322 NS 0.482 significant(P > 0.05). Cumulative distribution across days 1-11 after hatching, disregarding temporal se- ßNestling age 1-1! daysafter hatching. quence. bSpearman rank correlation coefficients;P < 0.05, except where indicated by NS. All n's = 23, except fruit load sizes (n = 20 for males, 19 for females, 21 for both sexes). ingbirds nested at least once more in 1981, and we had expectedfemales to feed at lower rates DISCUSSION in the latter daysof the nestlingperiod as they prepared for the next nesting attempt. How- Comparisonof feedingpatterns by malesand fe- ever, male predominancein the mid-nestling males.--Male and female mockingbirds made period may indicate that females conserve en- similar contributions to feeding nestlings, in ergy in this demandingperiod by feeding be- both quantity and types of food [although our low their maximal rate. When females increase data are from only a single year; see Witten- feeding rate later in the nestlingperiod, they berger (1982) for differencesamong years in (aswell asmales) typically bring a higher ratio male and female Bobolink (Dolichonyxoryzivo- of fruits to arthropodsthan do parentsfeeding rus) nestling feeding rates]. Some aspectsof younger nestlings.Females may then benefit temporalpatterns of feeding were different be- from providinga mixtureof foodsless costly tween the sexes,however. Equal overall feed- to obtain than a nestling diet of arthropods ing rates by the sexeshave been documented only, and the youngmay benefitdirectly from for a variety of monogamouspasserines (Ken- receiving more fruit (Breitwischet al. 1984). deigh 1952,Lack 1968, Best 1977, Knapton 1984). The greater percentageof unknown food In other passerines,females (e.g. Nolan 1978, itemsbrought to nestlingsby femalesresulted Pinkowski 1978, Howe 1979) or males (e.g. from greater female crypticity in delivering Biermann and Sealy 1982, Johnson and Best food, or because females delivered smaller, less 1982) provide more food. The reasonsfor these easilyidentified items, or both. Our impression differencesamong monogamousspecies are was that femaleswere more cryptic in nestvis- unknown, but we suspect the possible influ- itation behaviorthan males.This, in turn, may ence of the population breeding-adultsex ra- suggestthat males are at slightly greater risk tio. when feedingnestlings because of their great- Femalesdisplayed an increasein feedingrate er visibility. (both animalsand fruit) from day 1 to 11. The Total parental investment.--The resources feeding rate of animal prey by malesparalleled availableto parent mockingbirdsto convert to nestling growth rate and peaked in the mid- P! are time and energy; the same is true for all nestling period, when young grow most rap- animals.On spendingthese resourceson par- idly and food (especiallyprotein) requirements ticular behaviors,parents also incur the risk of are greatest. Similar patterns were found for injury or death. PI theory predictsthat parents Savannah Sparrows (Passerculussandwichensis; will spendtime and energy efficiently,weigh- B•dard and Meunier 1983).Most pairsof mocking risk, so as to maximize their lifetime fitness 156 BREITWlSCH,MERRITT, AND WHITESIDES [Auk, Vol. 103

(Fisher 1958, Trivers 1972). How males and fe- ture of time and energy (Zaias and Breitwisch males achieve this may be different. unpubl. data). In southern Florida, mocking- Factorsthat affectthe level of PI by a parent birds are multibrooded, and frequently pairs include: (1) the value of a given level of PI to build succeedingnests and femaleslay eggsand the young, (2) the ability of eachparent to pro- begin incubation while fledglings are still on vide additional PI, (3) the magnitude of decline their natal territories. In these instances, males in a parent's residual reproductive value for a provide fledglings with most of their food given level of PI, and (4) the probabilitythat a (Zaias and Breitwisch unpubl. data), as de- parent that desertsits mate and offspring will scribed for Song Sparrows (Melospizamelodia; find and mate with another individual (May- Smith 1978) and Chipping Sparrows (Spizella nard Smith 1977).If factor 1 or 2 is large or 3 passerina;Keller 1979). or 4 is small for one sex, a high level of PI by Comparisonof relative levelsof PI by mock- that sexwill be favoredby selection.Where PC ingbirds may be simplified by examining a sub- is the major portion of PI, these arguments setof majorcomponents of PI: nestbuilding by should also pertain to PC. Indeed, the advan- both sexes, egg production, incubation, and tages of PC (especially"nonshareable" forms brooding by females,defense of young by both of PC; sensuWittenberger 1979) to both sexes sexes(but more strongly by males), and fledg- have favored the evolution of monogamy in ling feeding (more by males).For a nestingat- many altricial birds (Wittenberger and Tilson tempt, males initially invest in laying the nest 1980). Trivers (1972) predicted comparable foundation of twigs. Femalesreduce this dis- levels of PI by males and females in monoga- parity as they line the nest with grasses,form, mous birds. lay and incubate eggs, and brood nestlings. We studied only one aspectof PI by mock- Malesdefend eggsand nestlingsmore strongly ingbirds,although feeding of nestlingsis prob- than females,the sexesfeed nestlingsat equal ably the largestsingle time and energy expen- levels, and males feed fledglings more. PI ex- diture by parents. Other aspects of PI by pendituresin a nesting attempt may therefore mockingbirdsinclude nestbuilding (malesand presenta cumulativepattern of investmentby females), egg production, sperm production, the sexesdifferent from that suggestedby Triv- incubationof eggsand brooding of young (fe- ers (1972) for monogamousbirds but like that males), feeding of fledglings (males and fe- suggestedby Burger (1981) for monogamous males), and defense of young (males and fe- BlackSkimmers (Rynchops niger) (see also Glad- males). Several of these investments (sperm stone 1979). Biedenweg (1983) directly mea- production, incubation, and brooding; King suredenergy expendituresby male and female 1973) are small relative to energy expenditure mockingbirdsin the breeding seasonand con- in feeding young, although incubationcan be cluded that males expendedat least as much time-consuming.Nest building is shared by energy in PI as did females. matesand requiresless time and energy than The influenceof the breeding-adultsex ratio.- feeding.Defense of youngis shared,with males What alternatives do the sexes have for time defending young more strongly than do fe- and energy expenditures?An obviousalterna- males (Merritt 1984, Breitwisch MS). tive for male mockingbirds is whether they Although the level of risk involved in feed- couldeffectively court other femaleswith time ing young is not known, it seemslikely to be made available by a reduction in PC. lessthan that incurred in defending eggsand The usual explanationfor a high level of PC nestlings (Breitwisch MS). Incubation and by male birds is that it is more profitablefor brooding also may involve risk; femalesper- malesthan engaging in a mixed strategyof de- form these duties and may be subjected to creasingPI and increasingmating effort (Em- greaterprobability of nocturnalpredation than len and Oring 1977,Mock 1983).That is, nest- roosting males (Lack 1954: Ch. 10). Whether lingsthat receiveless male PC fledgeat lighter risks incurred in the predominantly male de- weights or remain in the nest an extra day or fense of offspring more than offsetsany risks two, and this resultsin fewer young ultimately incurred by femalesin incubationand brood- reaching independence. In the extreme, no ing remains unknown. youngfledge when malesdecrease or withhold Both male and female mockingbirds feed PC (Wittenbergerand Tilson 1980).There may fledglings, and this is a considerableexpendi- also be direct benefits to males from maintain- January1986] MockingbirdParental Investment 157 ing a short nestling period in this population the quality of the young increasesas a result of becauseof high nestling predation (Breitwisch the male's increased efforts. unpubl. data). This argument assumesthat In this context, it is critical to know how the growth rate is responsiveto feeding rates and skewed sex ratio arises. There is no reason to that well-fed nestlingscan fledge soonerthan suspecta skewing of the sex ratio before the poorly fed nestlings(see Ricklefs 1983). end of PC; females are slightly smaller than However, the population sex ratio may dra- males and, if anything, we might predict bias- maticallyinfluence levels of PC. There is a male- ing in the oppositedirection (Lack 1954,Fisher biasedbreeding-adult sex ratio in this popula- 1958,Fiala 1981,Charnov 1982).Two remaining tion of mockingbirds,as documentedfor other alternatives are greater female mortality asso- passerines(Mayr 1939,Lack 1954,Trivers 1972). ciated with either greater distancesof female In each of six breeding seasons(1980-1985), natal dispersal,or the physiologicalrigors of there have been unmated, territorial males nesting,or both. If the former is of greaterim- (Merritt 1985, Breitwisch unpubl. data). In the portance (see Greenwood 1980), then females 1981 breeding season,between 6 May and 17 may indeed expend less PI than males. If the June, the sex ratio was 24 males: 18 females latter is more important (see Cody 1971), then (Merritt 1985). Furthermore, Merritt (1985) re- femalesexpend greater PI. In contrastto Triv- moved femalesfrom 11 pairs in this population ers's (1972) prediction, in the former alterna- in April 1983, and during the ensuing several tive, males would continue to compete for fe- weeks, no females replaced those removed. A males-the limiting sex--even though males female mockingbirdcan changeher mate if the would be the sex expendinggreater PI. Our male provides lessthan the desired level of PC, argument claims that mortality patterns of the and femalesin this population have changed sexes influence PI patterns to the extent that mates following nesting failure (Merritt and male birds may contribute more PI than fe- Breitwischunpubl. data). Males probablyhave males in other than polyandrousmating sys- little opportunity to change mates or acquire tems, in contrast to the arguments of Trivers additionalfemales. As a result,females may de- (1972) and Burley (1977). Last, in either alter- mand a level of male PC greater than males native, males may provide PC of greater im- would give if they could obtain additional portanceto the young (e.g. nest defense)than mates. that providedby females(Maynard Smith 1977). If the breeding-adultsex ratio were unity or In our view, the population breeding-adult biasedtoward females,males might be able to sex ratio is a critical piece of information nec- decrease their level of PC at no cost to their essaryto explain fully the particular patterns fitness(or increasetheir fitness if they could of PI by the sexes.We suggestthat females,as acquireadditional mateswith time made avail- the limiting sex in this mockingbird popula- able by reduced PC). This could occur because tion, may thus exert strong influence on male (1) females might compensatefor a reduced PC patterns. The large male contribution to level of male PC, sothe young would not suffer feeding nestlingsmay be a consequenceof this from this reduction because total PC remains influence.Similarly, male predominancein de- the same,or (2) the rate of gaining weight by fending eggs and nestlings and in feeding nestlingsmight decreasevery little, and young fledglings may be viewed as conditions fa- would fledge at only slightly lighter weights. vored by the skewedsex ratio. We predict sim- In both cases,males may not experience a re- ilarly high levels of male PC in populationsof duction in fitness. other birds characterized by male-biased A male would thus make time available for breeding-adult sex ratios. courting other females. The skewed sex ratio, however, makes it very unlikely that he will ACKNOWLEDGMENTS find an unmated female (see Pierotti 1981). Even if he does,his currentmate can punish him by We thank T. H. Fleming, P. A. Gowaty, S. M. Green, M.P. Hayes, F. C. James,O. T. Owre, T. D. Price, R. desertingafter raising the present brood; she C. Ritter, J. N.M. Smith, K. D. Waddington, J. F. hasoptions for rematingthat the male doesnot Wittenberger, J. Zaias, and two anonymousreview- have. The most profitable male behavior is to ers for commentsand suggestionson earlier versions invest more time and energy in caring for of the manuscript.Merritt's researchon mocking- young--and perhapstake on greater risks-- if birds was funded by the TropicalAudubon Society, 158 BREITWISCH,MERRITT, AND WHITESIDES [Auk, Vol. 103 the Frank M. ChapmanMemorial Fund of the Amer- HOWE,H. F. 1979. Evolutionary aspectsof parental ican Museum of Natural History, and the University care in the Common Grackle, Quiscalusquiscula of Miami Department of Biology. During the prepa- L. Evolution 33: 41-51. ration of this paper, Breitwischwas partially funded JOHNSON,E. J., & L. B. BESTß1982. Factorsaffecting by a TropicalBiology Fellowship from the University feedingand broodingof Gray Catbird nestlings. of Miami Department of Biology. This paper is con- Auk 99: 148-156. tribution No. 179 from the University of Miami De- KELLER,M. E. 1979. Breedingbehavior and repro- partment of BiologyProgram in Behavior,Ecology, ductive successof Chipping Sparrowsin north- and Tropical Biology. western Minnesota. Unpublished M.S. thesis, Grand Forks, Univ. North Dakota. KENDEIGH, S.C. 1952. Parental care and its evolu-

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King, and K. C. Parkes, Eds.). New York, Aca- WITTENBERGER,J. F. 1979. The evolution of mating demic Press. systemsin birds and mammals. Pp. 271-349 in ROY^M^,T. 1966. Factorsgoverning feeding rate, Handbook of behavioral neurobiology. Vol. 3, foodrequirement and broodsize of nestlingGreat Social behavior and communication (P. Marler Tits Parusmajor. Ibis 108:315-347. and J. Vandenbergh, Eds.). New York, Plenum SIEGEL,S. 1956. Non-parametricstatistics for the be- Press. havioral sciences. New York, McGraw-Hill. 1981. Animal social behavior. Boston, Dux- SKUTCH,A. F. 1976. Parent birds and their young. bury Press. Austin, Univ. Texas Press. 1982. Factorsaffecting how male and fe- SMITH,J. N.M. 1978. Division of labour by Song male Bobolinksapportion parental investment. Sparrowsfeeding fledged young. Can. J. Zool. Condor 84: 22-39. 56: 187-191. ., & R. L. T•LSON. 1980. The evolution of mo- TRIVERS,g. L. 1972. Parental investment and sexual nogamy: hypothesesand evidence. Ann. Rev. selection.Pp. 136-179 in Sexualselection and the Ecol. Syst. 11: 197-232. descent of man, 1871-1971 (B. Campbell, Ed.). Chicago, Aldine Press.

From "Third Meeting of the AmericanOrnithologists' Union" (1886,Auk 3: 117-118):

"It becameapparent more than a year ago that the riculture, not only brought the memorial favorably work of this Committee[on the Migration and Geo- to the notice of the Committee on Agriculture, but graphicalDistribution of North AmericanBirds--Ed.] afterward made an influential speechin its behalf on was fast assumingsuch formidable proportionsthat the floor of the Senate, and secured for the work the Union would soon be unable to sustain the fi- contemplatedan appropriationof $5000,after the item nancial burden thus entailed, and at the meeting of had been dropped in the House. It is thus to Senator the Union last year the Council was instructed to Miller that ornithologistsare indebted more than to preparea memorial to Congressasking for Govern- any other person for the appropriation, as without ment aid. In consideringthis matter the Council de- his efficient aid the appeal to Congresswould have cided to advise the establishment of a Division of been in vain. The House Committee on Agriculture, EconomicOrnithology under the Department of Ag- however, placed the work under the Division of riculture, which should not only carry on the inves- Entomology,instead of creating for it an indepen- tigationsnecessary to a thorough understandingof dent division, as contemplated in the memorial. the movements and distribution of our birds, but "The appropriationbecame available July 1, 1885, shouldalso enter upon a systematicinquiry into their at which time the investigationsin EconomicOrni- food-habitsand practicalrelations to Agriculture.The thology now in progressunder the Department of Chairmanof the Committeewas accordingly request- Agriculture were begun. The Council of the Union ed to prepare and presenta draft of a memorial, em- wasinvited by the Commissionerof Agriculture and bodying this plan, to the Council, which was in due ProfessorRiley--in recognitionof the interest in the time received and approved by the Council. The work manifestedby the Union, and of its effortsin Chairman,on presentingthis memorialto Congress, securingthe appropriation from Congressfor these was accordeda hearing before the House Committee investigations--to nominate a personto take charge on Agriculture, through the assistanceof Prof. C. V. of, and conduct, the work. This the Council did at a Riley, Chief of the Division of Entomology of the meetingheld in Washingtonon the 21stof last April, Departmentof Agriculture.Prof. SpencerF. Bairdhad unanimouslyand very fittingly selectingfor this po- the kindnessto appear before the Agricultural Com- sition the Chairman of the A. O. U. Committee on mittee and personallyurge the practicalimportance the Migration and GeographicalDistribution of North of the investigationsthus proposed,while Senator American Birds, Dr. C. Hart Merriam, to whom also Warner Miller, Chairman of the Committee on Ag- had fallen the labor of presentingthe memorialand

(continuedon p. 203)