THE BARN OWL EGG: WEIGHT LOSS CHARACTERS, FRESH WEIGHT PREDICTION AND INCUBATION PERIOD JAMES D. MARSHALL, CLAIRE H. HAGER AND GWYN MCKEE

Size: px

Start display at page:

Download "THE BARN OWL EGG: WEIGHT LOSS CHARACTERS, FRESH WEIGHT PREDICTION AND INCUBATION PERIOD JAMES D. MARSHALL, CLAIRE H. HAGER AND GWYN MCKEE"

May Page
5 years ago
Views:

1 THE BARN OWL EGG: WEIGHT LOSS CHARACTERS, FRESH WEIGHT PREDICTION AND INCUBATION PERIOD JAMES D. MARSHALL, CLAIRE H. HAGER AND GWYN MCKEE ABSTRACT. -- A ttal f 177 Cmmn Barn-Owl (Tyr alba pratincla) eggs prduced by 14 captive pairs were studied during the spring f 1985, Initial egg parameters fr 75 eggs were fresh weight ( g), length ( mm) and breadth ( mm). Using these data, a cefficient (Kw) unique t the barn wl egg was calculated fr Hyt's (1978) equatin fr predicting the fresh weight f an egg. (K w =.5453) Fr 5 artificially incubated eggs (hatchability = 93.5%) the lay t pip (LP) interval was d, the pip t hatch (PH) interval was d and the verall incubatin perid was d. Variance in the latter perid (range: d) may have been due t an bserve delay in initial embrynic develpment f frm 1-7 d. During incubatin, several externally quantifi- MATERIALS AND METHODS able changes ccur in the avian egg. These include: The barn wl breeding clny f the Raptr Rehabilitatin and 1) the relatively steady reductin in weight due Prpagatin Prject, Inc., Eureka, Missuri, was established in 1979 and prduced mre than 15 juvenile wls yearly thrugh mainly t lss f water vapr by diffusin frm the 1986 fr release int Missuri. The clny cntained nn-sibling embrynic chriallantis thrugh the prus shell breeding pairs cllected frm eastern Nrth America. Each pair and its evapratin at the eggshell surface was hused in an utdr mew in a natural setting and was fed daily a diet f fresh rdents ad libitum. Human disturbance was (Rmanff and Rmanff 1949; Ar and Rahn nrmally limited t 2 shrt intervals. 198); and 9) the equal exchange f s and COs Barn Owls will naturally prduce > 1 clutch f 6-8 eggs during favrable seasns (Eckert and Karalus 1974), and ften breed gases thrugh the eggshell by the chriallantis - a repeatedly all year in captivity (Mendenhall, pers. cmm.). Thus, 2 prcess nt affecting weight lss (Wagensteen and clutches/pair f wls were assured. The first clutch prduced by Rahn 197, 1971). The mean percentage f fresh each pair was remved fr artificial incubatin and subsequent clutches were left with the parents fr natural incubatin. egg weight (W) lst during the incubatin perid Beginning in early January, apprximatley 2 wks befre initiafr many avian species ranges frm 12-18% (Drent tin f barn wl breeding, each mew was entered daily by 1 r 2 197). Prper weight lss is crrelated with hatcha- wrkers and the nest bxes were checked fr eggs. This prcedure was cmpleted at a prescribed time every mrning thrugh April bility and nrmal embrynic develpment t ensure that n egg was lder than 24 hr when initially mea- (Walsberg 198). During artificial incubatin, accusured, and t minimize nn-randm disturbance f the adult wls. As each freshly laid (+ -24 hr) egg was discvered, it was weighed rate regulatin f egg weight reductin is pssible n an electric field balance t determine W, and the dimensins thrugh a variety f methds; (Burnham 1983; were measured with a Vernier caliper. Additinally, each fresh Weaver and Cade 1983). egg was marked with a graphite letter crrespnding t its sequence in the clutch. N egg was ever fully remved frm the nest A mathematical equatin (1) based upn egg bx and adults were kept at a distance during measurement. length (L) and breadth (B), parameters which are During the subsequent incubatin perid, each egg was weighed invariant during incubatin, was develped by every ther day using similar methds. T reduce parental stress and prmte successful cpulatin, Hyt (1978) t predict avian W. n eggs were cllected frm nest bxes prir t clutch cmpletin W= KwLB (1) (W.C. Crawfrd, Jr. pers. cmm.). Egg laying interval was apprximately 1 egg every 2-3 d, thus eggs were frm 1 t 16 d ld The cefficient (Kw) f this equatin interrelates when remved frm the nest fr artificial incubatin. Eggs were shell measurements, and may be adjusted t ac- incubated in Rll-X RX2A autmatic rlling incubatrs with a cmmdate a single species fr accurate W fr cnstantemperature f 37.5 ø C, and relative humidity f 48%. Each egg was rlled manually 18 ø 3x/d t supplement autmatic Peregrine Falcn (Falc peregrinus) eggs, and als rlling. Thrughut the lay-t-pip (LP) interval, each egg was bserved a reductin in W f % during weighed and candied every ther day t determine bth weight incubatin f nrmal eggs. Hwever, ur study f lss and crrespnding embrynic develpment. Once an embry had pipped its shell, the egg was placed pipped side upwards in the incubatin f cmmn Barn-Owl (Tyt alba anther Rll-X RX2A set at a lwer temperature (35øC) but higher practincla) eggs indicates that they cannt be pre- relative humidity (6%). Pipped eggs were nt turned. During the pip-t-hatch (PH) interval, n weight measurements were made cisely characterized by values develped fr Peregdue t shell fragility and difficulty in determining weight at the rine Falcn eggs. Our bjective was t measure barn instant f hatching. Infertile eggs r eggs cntaining dead emwl egg weight lss and incubatin perid, and brys were remved frm the incubatrs t inhibit bacterial grwth. algin Hyt's equatin fr this species. Eggs underging natural incubatin were weighed similarly thrugh pipping, but nly ccasinally candied t reduce nest disturbance. N extra care was prvided fr these clutches (i.e. cleaning f nest bxes, bad egg remval, etc.) unless a shell failed 18 RAPTOR RESEARCH VOL. 2 (3/4): 18-! 12

2 FALL/WINTER!986 THE BARN OWL ECC 19 Table 1. Mean ttal fractin f grams W lst ver the 28 d lay t pip interval fr Barn Owl eggs a incubated artifically and naturally. INCUBATION N B SD MIN/MAX CASES C r d Artificial Natural a Only fertile, successful hatching eggs represented. b Number f eggs. c Number f pints used in generating r values and regressin lines give Figure 1. d Crrelatin cefficient relating cumulative fractin f W lst day f incubatin. in a fertile egg; such eggs were remved fr artificial incubatin and excluded frm the study. T prevent cannibalism, an ccasinal aspect f barn wl adult-chick behavir, the amunt f fd prvided fr each mew was increased cnsiderably fllwing the hatch f each egg (W.C. Crawfrd Jr., pers. cmm.). Statistical analysis was perfrmed using Statistical Package fr the Scial Sciences (SPSS)(Nie et. al. 1975). A regressin line develped by the least squares fit was generated pltting the cumulative fractin f W lst by crrespnding interval day. The resulting linear equatin was used as a mdel (assuming 28 d LP interval) t predict the ttal fractinal weight lss fr all cases in each f the 2 incubatin type categries. Other SPSS ptins were used t generate F-Test, t-test, Pearsn's r and Chi-squared (X 2) values and prbabilities. RESULTS The mean ttal fractin f W lst during the LP interval was significantly different (F = 7.5 df = P <.1) between artificially and naturally incubated eggs which hatched successfully (Table 1). High degrees f crrelatin were fund between cumulative reactin f W lst and interval day within each incubatin grup, implying that eggs dehydrated similarly in their respective categries althugh a wide range f ttal fractin f W lst by individuals was nted. We defined hatchability as the percent f fertile eggs successfully hatched. The hatchability f naturally incubated eggs was 8.9% (n = 62). Hatchability between incubatin types was significantly different (X 2 = 4.56; df-- P <.5). The relatinship between day f incubatin and cumulative fractin f W lst was examined (Fig. 1). An increase in the spread f pints (statistically indicated by increasing standard deviatins f residuals) frm the regressin line (Table 2), and crrespnding decrease in crrelatin cefficients as incubatin prgressed thrugh cnsecutive seg- ments f LP interval were fund. Bth incubatin types had this characteristic. A species specific cefficient (K w =.5453) was determined using equatin (1) fr W predictin and the measured values f W, L and B cllected frm 75 barn wl eggs (Table 3). Using this K w a strng crrelatin was fund between directly Table 2. Increasing deviatin f pints frm regressin lines indicated by increasing standard deviatin f residuals and decreasing crrelatin between fresh W lst and incubatin day. INCUBATION CASES A r P RESIDUAL SD Artificial -1 days days days Natural -1 days days days a Number f pints used in generating the r values and regressin lines given Fig. 1.

3 11 MARSHALL ET. AL. VOL. 2, NO. 3/4 H J Y ) -.2;: 56 ARllFlCtN. INCUBAllON CASES: ) 5-6 G 7-8 >9t 7 I I lo II 17 li 11 2: I 2 3 NATURN_ INCUBATION Iii > J øø ( Oc!! [ i f i i I I i ß : I 17 lb It : I -J,I 3 DAY OF INCUBATION Figure 1. Regressin f cumulative fresh weight lst in barn wl eggs by day f incubatin.

FALL/WINTER 1986 THE BARN OWL EGG 111 Table 3. Summary f physical parameters frm natural incubatin and perid f incubatin fr cmmn Barn-Owl (T.a.pratincla) eggs incubated artifically.

4 FALL/WINTER 1986 THE BARN OWL EGG 111 Table 3. Summary f physical parameters frm natural incubatin and perid f incubatin fr cmmn Barn-Owl (T.a.pratincla) eggs incubated artifically. PARAMETER N SD MIN/MAX Length (1)(mm) Breadth (B) (mm) Fresh Weight (W)(g) Lay t Pip (LP) Interval (days) Pip t Hatch (PH) Interval (Days) Incubatin Perid (days) measured and calculated values fw (r =.917; P <.1); the 2 grup means were similar (t-test =.39; P =.71). When the cefficient K w;.5474 develped by Burnham (1983) was used in equatin (1), strng crrelatin (r =.917; P <.1) was als evident between measured and calculated values f W, althugh statistical cnfidence in the similarity between the 2 grup means was decreased (t-test = 1.86; P =.67). DISCUSSION The ttal incubatin perid f the barn wl can be generalized frm the literature as 3-33 d, with extremes f 29 and 34 d (Eckert and Karalus 1974; Bunn et. al. 1982). Our study indicatd a similar mean incubatin perid and range. The mean W value (Table 3) f the barn wl eggs studied is incnsistent with the mean (W) develped frm the single randm sample cllected (frm the wild) by Sumner' (1929), and his values were reprted in ther wrks (Drent i97; Ar and Rahn 198). Hwever, Hyt (1978) nted that intraspecific variability in the values f W, L and B began their develpment immediately, and shwed a blastdisc within 24 hr. A sharp increase in the rate f egg weight lss in cnjunctin with abrupt initializatin f embrynic develpment in drmant-fertile eggs was rutinely bserved. After an extremely lw rate f daily weight lss, these eggs suddenly achieved a relatively cnstant rate f weight lss which cntinued fr abut 28 d until a nrmal fractin f W was lst. The chicks then pipped the eggshell. Thus, a specific weight lss rate ccurred fr the latter prtin f the LP interval, althugh this interval may have been initially extended by the drmant-fertile cnditin. Since the PH interval was fairly cnstant, with variance prbably due t bservatinal errr, nearly all deviatin in the barn wl incubatin perid was due t the initial drmant-fertile egg. It was unclear whether the drmant-fertile cnditin was randm r relative t ther eggs' develpment within clutches, but eggs generally hatched in sequence f their laying. Quantificatin f this embrylgical characteristic was nt pssible using their sample and further study is required. Althugh hatchability and mean ttal fractin f culd be expected and we have attempted t accunt fr W lst was related t incubatin type (natural vs such deviatin thrugh relatively large samples cllected artificial), the 2 incubatin methds are very diffefrm many pairs f wls within the subspecies T. a. rently affected. Factrs inherent nly during pratincla. natural incubatin include frequent variatin in Careful, frequent illuminatin f eggs with cl, nest micrclimate and ambient temperature and high intensity light prvided gd visual tracking f humidity, high bacterial expsure, and vilent embrynic develpment. A small fractin f em- mvement f delicate eggs by disturbed adult wls. brys did nt achieve the visible blastdisc stage Such relatively uncntrllable variables may have (indicative f fertility) fr up t 7 d fllwing the caused natural incubatin weight lss rates t ccur date f laying. Hwever, mst embrys apparently which d nt parallel thse f eggs in undisturbed

5 112 MARSHALL ET. AL. VOL. 2, N. 3/4 nests. These adverse factrs undubtedly cntributed t the lwer hatchability f fertile eggs underging natural incubatin, althugh the sample analyzed includes many eggs frm undisturbed nests. ACKNOWLEDGMENTS We thank the Raptr Rehabilitatin and Prpagatin Prject, Inc., and W. C. Crawfrd,Jr., wh has reintrduced ver 5 barn wls in Missuri. LITERATURE CITED AR, A. AND H. RAHN Water in the avian egg verall budget f incubatin. Amer. Zl. 2: BUNN, D.S., A.B. WASHBURTON, AND R.D.S. WILSON The Barn Owl. Bute Bks, Inc. Vermillin, Suth Dakta. p. 22. BURNHAM, W. Artificial incubatin f falcn eggs. J. Wildl. Manage. 47: BRENT, R Functinal aspects f incubatin in the Herring Gull. Behaviur Suppl. 17:1-32. ECKERT, A.W. AND K.E. KARALUS The Owls f Nrth America. Dubleday and C., Inc. Garden City, New Yrk. pp Regressin f weight lst by interval day reveals an increase in deviatin between predicted and actual egg weights during the LP interval. Since weight lss is due t expired water vapr, as previusly cited, this unexpected trend may reflect differential individual respiratry functin, effected by the chriallantis in cnjunctin with the eggshell, which was nt subject purely passive diffusin. HOYT, D.F Practical methds f estimating vl- This result cntrasts with recent literature which ume and fresh weight f birds' eggs. Quk 96:73-77 cites simple diffusin dwn cncentratin gra- NIE, N.H., C.H. HULL, J.G. JENKINS, K. STEINBRENNER dients as the single frce mving gases acrss the AND D.H. BENT Statistical Package fr the Scial Sciences, 2nd Ed. McGraw-Hill Bk C., New eggshell (Wangensteen and Rahn 197, 19721). Yrk. Inferences drawn frm these results are in- RAMANOrE, AL. AND A.J. ROMANOEE The Avian teresting t bth the eclgist and the cnser- Egg. Jhn Wiley and Sns, Inc. New Yrk, p vatinist prpagating this species artifically. Tyt SUMNER, E.L. JR Cmparative studies in the alba supp. pssess extremely favrable reprduc- grwth f yung raptrs. Cndr 31: tive capabilities. Develpmental flexibility is re- WALSBERC, G.E The gaseus micrclimate f the flected in the variable egg weight lsses achieveable avian nest during incubatin. Amer. Zl. 2: during incubatin and in the drmant-fertile cn- WANOENSTEEN, O.D. AND H. RA8N. 197/71. Respiratry ditin which allws extensin f incubatin perid. gas exchange in the avian embry. Respiratin Physil. 11:1-45. These factrs may cntribute t the high hatchability evident frm the data in this study. WEAVER, J.D. AND T.J. CADE Falcn prpagatin: a manual n captive breeding. The Peregrine Fund, Inc. Ithaca, New Yrk. Raptr Rehabilitatin and Prpagatin Prject Inc., Bx 193, Eureka, Missuri Current address f first authr: 117 Bradway, New Orleans, Luisiana Current address f secnd authr: Bx 193, Eureka, Missuri Current address f third authr: Bx 27, Bartlesville, Oklahma Received 1 February 1986; Accepted 3 Nvember 1986.

1 '~; c\ 1.Introduction

$1 '~; c\ 1.Introduction$ CHAPTER - H 1 '~; c\ REPRODUCTIVE BEHAVIOUR OP GERBILS V RETRIEVAL OP YOUN& 1Intrductin 'Retrieval 1 r carriage f straying r fallen yung t the nest by 1actating mthers, frms an Imprtant cmpnent f the maternal