108 SHORT COMMUNICATIONS IBIS 118

REFERENCES BANNERMAN, D. A. 1949. Birds of tropical West Africa. Vol. 7. London: Crown Agents. BROWN, L. & AMADON, D. 1968. Eagles and falcons of the world, Vol. 1. Middlesex: Country Life. DURANGO, S. 1949. The nesting associations of birds with social insects and with birds of different

species. Extracts translated from the Finnish. Ibis 91 : 140-143. FRY, C. H. 1965. The birds of Zaria. Bull. Niger. Om. SOC. 2: 68-79. GOSSE, P. H. 1847. The birds of Jamaica. London: John van Voorst. KEAY, R. W. J. 1953. An outline of Nigerian vegetation. Lagos: Govt Printer. MACKWORTH-PRAED, C. W. & GRANT, C. H. B. 1960. African Handbook of Birds, Series I. Birds

MEINERTZHAGEN, R. 1959. Pirates and predators. The piratical and predatory habits of birds.

MOREAU, E. E. 1942. The nesting of African birds in association with other living things. Ibis (14)

VAN SOMEREN, V. G. L. 1956. Days with birds. Fieldiana Zool. 38: 1-520.

of Eastern and Northeastern Africa, 2nd Vol. 2. London: Longmans.

Edinburgh and London: Oliver Boyd.

6: 240-263.

WHO Onchocerciasis Control Programme, B.P. 549,

Ouagadougou, Republic of Upper Volta

8 September 1974

J. FRANK WALSH BRENDA WALSH

WEIGHT AND BODY COMPOSITION IN NESTLING BLUE TITS PARUS CAERULEUS

Nestling Great Tits Parus major and Blue Tits Parus cueruleus vary greatly in weight, and recaptures of ringed young show that fewer of the light than of the heavy nestlings survive to the following winter (Lack, Gibb & Owen 1957, Perrins 1965, Schifferli 1973). The reason for this correlation is unknown, but Perrins (1965) has suggested that the extra weight of the heavier young probably consists mainly of subcutaneous f a t ; this would then act as a food reserve in the immediate post-fledging period, when it may be difficult for the young to obtain enough food (Royama 1966). An alternative explanation, however, is that the lighter young are restricted in their development of body structure, so that when they do fledge they are functionally less efficient than are normally growing young. The present report shows that in Blue Tits variation in fat content is in fact the major effect, though accompanied by other changes in body composition.

MATERIALS AND METHODS

The results reported here are based on analyses of 19 Blue Tits nestlings aged 13-18 days (day of hatching = day 0) taken under government licence from nest box broods in Wytham Wood, near Oxford, during the summers of 1970 and 1971. Ten birds were killed within an hour of removal from the nest, being collected specifically for body composition studies of ‘normal’ young. The remaining young comprised six birds killed after use in respirometry experiments and three birds which died during one such experiment. These ‘experimental’ birds were used in experiments conducted overnight and were therefore dependent on metabolic reserves accumulated during the day’s feeding; their analysis therefore provided data on the resources used during metabolism (see O’Connor 1975a, for details of respirometry methods). The nine differed considerably as to the experimental conditions to which they were exposed, since they were used in the pilot runs establishing conditions acceptable for nestlings in subsequent experiments ; major experiment-dependent effects-for example, excessive water loss-were, however, unlikely to have been present, and the rates of overall weight-loss observed were com- parable with those recorded in similar studies (Mertens 1969, van Balen & CavC 1970).

1976 SHORT COMMUNICATIONS 109

I I I I 1

0 . 0

Carcases were weighed, dissected into a number of body components (see Table 2) and oven-dried for three days ; lipids were then extracted from the dried components using diethyl ether in a standard Soxhlet extractor.

RESULTS

The mean weight of all nestlings when first weighed, i.e. prior to any experiments in the case of ‘experimental’ birds, was 10-7ks .~ . 1.0 g; this is similar to the mean weight at fledging of 11-0f0.7 g obtained from field measurements (O’Connor 1975a). Since body- weights decrease during the last week in the nest by an average of only 5%, the weights of the nestlings analysed can be taken as representative of normal weights at these ages. The mean weight of the nine birds subsequently used in metabolic experiments was 10.7&0.9 g, almost identical to the mean of l l .7 f l .2 g for the ten killed immediately ( t = 0.1, n.s.); differences in body composition found between the two groups on analysis were therefore due to metabolic consumption of resources.

0 0 .

0

0

0

I 1 I I I I 1 6 7 8 9 10 II 12 13

Weight (4) FIGURE 1. Fat content in relation to body-weight in nestling Blue Tits. ‘Experimental’ birds

(see text) are shown by open circles. The overall correlation between fat and body-weight was 0.938 (P<O.OOl).

Fat content varied linearlywith body-weight in both groups (Fig. 1) and was correlated with 88.0% of the overall variation in body-weight (Y = 0.938, P<O.OOl). Analysis of the two groups separately also yielded statistically significant correlations (Y = 0.867, P<O-01 for ‘normal’ birds; Y = 0-764, P<O.O5 for ‘experimental’ birds), and this was also true of partial correlations calculated to remove the effects of any differences due to the spread in nestling age (yP = 0.791 for normal birds, Y, = 0.764 for experimental birds, P<0.05 in both cases). Inspection of Figure 1 shows that fat reserves were con- sumed to fuel the metabolism of the experimental birds.

110 SHORT COMMUNICATIONS IBIS 118

Mean changes in body constituents during metabolism are summarized in Table 1. Fat was clearly the most heavily depleted constituent but changes in lean dry material (mainly protein) also took place. Since this was apparent in nestlings which still had an average of 220 mg (minimum 144 mg) of lipid present, protein consumption must have commenced before fat reserves were fully depleted.

TABLE 1

The effect of metabolism on body constituents in nestling tits

Constituent (9)

Difference as % of

Normal birds Experimental birds normal Mean f S.D. Mean f S.D. level t-test'

Weight Water Lean dry weight Fat

10.68 1.18 7.72 0.85 -27.7 6.18*#* 7.289 0.650 5.409 0.674 -25.8 6.19*** 2.501 0.365 2.086 0.232 -16.6 2.92** 0'885 0.245 0'220 0.064 -75.1 7.88***

Note: =Student's t test: ** P<O.Ol *** P<O.OOl

The distribution of this change in body protein over a number of body organs is shown in Table 2. All components examined decreased in absolute weight but the larger relative losses were from the digestive organs-liver, gizzard and alimentary tract-and those components with large muscle content, such as the pectorals and legs. The result of such differential losses was to change the relative proportions of these organs in the

TABLE 2

Distribution of lean dry material before and after nestling metabolism

Absolute size of component Relative size of component' Normal Experimental Change as Normal Experimental Change as

O / birds birds % of birds birds /o of normal normal

Component (mg) b g ) level level

Liver 93 35 -62.4***2 3.8 1.6 -57.1*#*2 Gizzard 119 58 -51*3*** 4.8 2.8 Alimentary tract 124 77 -37.9*** 4.9 3.7 -25.2*' Lungs 21 14 -33.3 0.8 0.6 - 22.2 Pectoral muscles 224 147 -34.4'' 8.8 7.0 - 20.0* Heart 27 21 -22.2 1.1 1.0 - 9.3 Body shell 397 32.5 -18.1** 15.9 15.6 -1.8 Legs 323 284 -12*1* 12.9 13.7 +5*8* Wings 208 183 -12.0 8-3 8.8 +6.5 Head 248 237 -4,4 10.0 11.4 + 14*3*** Integument 71 7 707 - 1.8 28.8 33.8 +17.4

-41.5'**

Notes: 100 x lean dry weight of component/total lean dry weight of nestling. 2 Significance of difference tested by Student's t-test: * P<O*O5

** P<O.01 *** P < O * O O l .

1976 SHORT COMMUNICATIONS 111

birds consuming their reserves, as shown in the final column of Table 2. This shows that the integument, head and legs were disproportionately large in these birds whilst the digestive organs and flight muscles were disproportionately small. Part of the effect for the alimentary tract was probably due to differences in intestinal contents, as these were not removed during dissection.

DISCUSSION

Variation in the fat content of nestling Blue Tits taken directly from their nests was correlated with much of the variation in total body-weight, this confirming Perrins’ (1965) suggestion. The energy requirements of newly fledged titmice are apparently higher than those of nestlings of any age (Royama 1966), principally because the young no longer huddle together to conserve heat (Mertens 1969, O’Connor 1975b); their greater fat reserves would then afford heavier young a higher survival rate than obtains amongst lighter young. Furthermore, since caterpillar abundance varies from year to year the need for fat reserves must vary also, and Perrins (1965) has in fact found that the effect of body-weight on subsequent survival does vary markedly between years. Variation in body-weight in nestling titmice can therefore be attributed to corresponding variations in fat content.

The analysis of body components in normal and experimental nestlings showed that protein, carbohydrate and water were also lost during metabolism, principally from the digestive and muscle components. These changes parallel those in adult birds, as diurnal changes in response to feeding activity have been demonstrated in Red-winged Black- birds Ageluius phoeniceus and Starlings Sturnus vulgaris (Fisher & Bartlett 1957) whilst the sarcoplasm of the pectoral muscles has been shown to serve as a protein reserve in the Red-billed Quelea Quelea quelea (Kendall et al. 1973). On the other hand virtually no material was removed from the head and the integument, so that these components were disproportionately large in experimental birds. This reflects the survival value of these components, the head with the brain, mouth and eyes affecting all other functions whilst the integument insulates the nestling against excessive heat loss and still further depletion of its metabolic reserves. However, although the major depletions are from tissues not immediately essential to the continued survival of the nestling the resulting changes in the size of these components must reduce their subsequent efficiency and thus contribute to the greater mortality of these young as fledgelings.

I am grateful to Dr C. M. Perrins for discussion of the results and to Dr L. T. Threadgold for reading the manuscript. The work was carried out during tenure of a Nuffield Foundation Biological Scholarship and this support is gratefully acknowledged.

REFERENCES

FISHER, H. I. & BARTLETT, L. M. 1957. Diurnal cycles in liver weights in birds. Condor 59: 364-372. KENDALL, M. D., WARD, P. & BACCHUS, S. 1973. A protein reserve in the Pectoralis major flight

muscle of Quelea quelea. Ibis 115: 600-601. LACK, D., GIBE, J. & OWEN, D. F. 1957. Survival in relation to broodsize in tits. Proc. zool. Soc.,

Lond. 128: 313-326. MERTEXS, J. A. L. 1969. The influence of brood size on the energy metabolism and water loss of

nestling Great Tits Parus major major. Ibis 111 : 11-16. O’CONNOR, R. J. 1975a. Growth and metabolism in nestling passerines. In Peaker, M. (ed.)

Advances in avian physiology. Symp. zool. SOC., Lond. 35: 277-306. O’CONNOR, R. J. 197513. The influence of brood size upon metabolic rate and body temperature

in nestling blue tits Parus caeruleus and house sparrow Passer domesticus. J. Zool., Lond. 175: 391-403.

PERRINS, C. M. 1965. Population fluctuations and clutch size in the Great Tit (Parus major). J.

ROYAMA, T. 1966. Factors governing feeding rate, food requirement and brood size of nestling anim. Ecol. 34: 601-647.

Great Tits Parus major. Ibis 108: 313-347.

112 SHORT COMMUNICATIONS IBIS 118

SCHIFFERLI, L. 1973. The effect of egg-weight on subsequent growth in nestling Great Tits. Ibis

VAN BALEN, J. H. & CAV& A. J. 1970. Survival and weight loss of nestling Great Tits, Purus major, 115: 549-558.

in relation to brood-size and air temperature. Neth. J. Zool. 20: 464-474.

Edward Grey Institute of Field Ornithology, RAYMOND J. O'CONNOR University of Oxford,

South Parks Road, Oxford

1 October 1974

Present address: Department of Zoology, Gwynedd, LL57 2UW.

University College of North Wales, Bangor,

DESERTION AND ABNORMAL DEVELOPMENT I N A COLONY OF SOOTY TERNS STERNA FUSCATA INFESTED BY

VIRUS-INFECTED TICKS

There have been several instances reported of mass desertion at tern colonies. Marples & Marples (1934) suspected that food shortage caused birds of a Sandwich Tern Sterna sandvicensis colony to desert, and Austin, Robertson & Woolfenden (1972) suggested that a mass failure of Sooty Terns S.fuscata in the Dry Tortugas in 1969 might have been caused by frequent sonic booms over the colony. Marshall (1942) described the night desertion of Common Terns S. hirundo, and their return to incubate during the day, but was unable to suggest a cause.

During a study of the biology of Sooty Terns on Bird Island, Seychelles (55' 12' E, 3" 43's) (Feare 1973), no abnormal behaviour was noticed in the 1972 season, nor in most of the colony in 1973. Egg losses away from the colony edge averaged about 25%, and territories from which eggs were lost were quickly re-occupied by other pairs of birds (Feare in prep.). Of 264 chicks whose histories from hatching to death or flying were followed, none was deserted shortly after hatching. However, in a part of the colony mass desertion of well-incubated and hatching eggs, and of newly hatched chicks, was observed in 1973. In this season peak laying occurred between 8 and 17 June, and on 14 July an area (c. 25 m2) of eggs, some of them broken and all without attendant adults, was noticed in a shallow valley at the northern end of the colony. The broken eggs had been predated by Turnstones Arenaria interpres and rats Rattus rattus, but the presence of intact but cold eggs in this area suggested that predation was not the factor causing desertion. After 14 July the area of desertion spread rapidly, and by 5 August 5000 pairs were estimated to have deserted their well-incubated eggs or newly hatched chicks (Plate 1).

During daytime there was no indication of what was causing the adults to desert; but on a visit to the affected area at night on 18 July, it was noted that adults were more restless around the deserted area than elsewhere in the colony, and that the ground was covered with argasid ticks (subsequently identified by Drs H. Hoogstraal and M. N. Kaiser as Ornithodoros capensis). The legs of observers standing in this area quickly be- came covered with ticks, whereas in the main part of the colony, where no desertions had occurred, no ticks were found either on the ground or on observers. All bites sustained by people visiting the colony at night, except for one on the upper back, were around the pubic hair, and they left a severe itch which lasted for several days. Collections of ticks during this period consisted almost entirely of nymphs.

In 1972 none of the people working in the colony was aware of the presence of ticks, despite many hours spent sitting in the colony handling chicks, but in 1973 by 22 August