Nesting biology of the Black-necked Grebe

Transcription

1 Bird Study ISSN: (Print) (Online) Journal homepage: Nesting biology of the Black-necked Grebe Zygmunt Bochenski To cite this article: Zygmunt Bochenski (1961) Nesting biology of the Black-necked Grebe, Bird Study, 8:1, 6-15, DOI: / To link to this article: Published online: 18 Jun Submit your article to this journal Article views: 172 View related articles Citing articles: 1 View citing articles Full Terms & Conditions of access and use can be found at Download by: [ ] Date: 10 January 2018, At: 15:31

2 Nesting biology of the Black-necked Grebe By Zygmunt Bochenski (Dept. of Animal Psychology, Jagiellonian University; now Cracow Branch of the Zoological Institute of Polish Acadamy of Sciences) Received I December INTRODUCTION THE BLACK-NECKED GREBE (Podiceps caspicus) is a very common bird in almost all parts of Central Europe where it is characteristic of small freshwater lakes and fish-ponds. It nests among water plants such as water grass, reeds, irises or rushes, singly or in colonies which vary in numbers of nesting pairs. The Black-necked Grebes very often nest in mixed colonies, together with Black-headed Gulls (Larus ridibundus), Black-tailed Godwits (Limosa limosa), ducks, Moorhens (Gallinula chloropus), and other water birds. The quantitative relations between the species in such colonies are variable and there are colonies in which Black-necked Grebes are dominant and others in which they are only an additional species. In Central Europe the breeding season begins in the second half of May, when the birds build their nests and lay 3-5 eggs. Incubation lasts till the second half of June, when the nestlings hatch and leave the nests. FIGURE I. Section of a Black-necked Grebe's nest. The arrows indicate places where the temperature of the nest material was measured : (I) in the mass of the nest material under the surface of water ; (2) in the layer immediately under the eggs and (3) in the material covering the eggs. NEST BUILDING It is well-known that all species of grebes build floating nests which are anchored by being among water plants. Most of the nest mass is underwater and only a flat disc emerges above. The disc is a few centimetres high and there is a shallow nest cup in it. The bottom of the cup is 6

3 GREBE NESTING BIOLOGY very often level with the water surface so that the eggs lie on a wet substratum or just in water (see Fig. I). The nest is built of fresh (green) and rotting (brown) pieces of water plants which both parents gather on the water surface or pick up from the lake bottom in the vicinity of the nest. This material is usually soft and pliable and the birds can shape the nest easily. TABLE I-NEST DIMENSIONS AND NUMBER OF EGGS (Measurements in centimetres) Ser. no. Outer diameter Extremes average Inner diameter Extremes average Height above water Number Cup of depth eggs Notes I 22X 20 2I 14X single z 34X X single 3 30X X single, distant from the nest of Coot 4 25X X 10.5 Io oX3o 30 12XII X27 27 IIXII II (3 eggs and r nestling) 7 3oX30 3o I2X X X X IOXIO IO IC 23 X I0.5 X II II 23X23 23 IoXIO IO colony 12 26X26 26 IIXII II X24 24 IIXII II X IOX I0.5 I X X X28 28 IoXIO Io X rox X IoXIO Io X26 26 IIX1r II X25 25 MX 10 IO I z6x X The nest sizes vary with the same species of grebe. The dimensions of the nests of Black-necked Grebes are shown in Table I. The table gives the measurements of the outer and inner diameters of the nest, as well as their average diameter, the height of parts emerging from water, the depth of cup and the number of eggs laid in each of at nests. In the zr nests specified in Table I the outer diameters range from 20 to 34 cm. whereas the inner diameters are from 9 to 25 cm. The variation, especially in the shortest diameters, is greater than with other species of birds where this dimension is more constant e.g. Spotted Flycatchers (Muscicapa striata) (Bochenski, 1957). The dimensions of these nests are directly related to the size of the bird making the nest cup (Promptov, 0945). Naturally, the inner diameter of the nest of a Black-necked Grebe also depends on the size of the bird but only to a small degree. 7

4 BIRD STUDY It is also influenced by the number of eggs laid in the nest, as is shown in Table II. The distribution of measurements of the nests indicates the inter-dependence of the average inner diameter of the nest cup and the number of eggs. It is clear that this dependence is connected with the poor elasticity of the nest material. TABLE II DEPENDENCE OF NEST CUP DIAMETER UPON THE NUMBER OF EGGS IN THE CLUTCH Clutch Inner diameter of nest cup (cm.) size 9.I to I0 Io.I to I I I I.I to I2 I2.1 to to to I o o I 4 o I The description of a grebe's nest would be incomplete without mention of the widely known fact that the eggs are covered with nest material by the brooding birds when they leave the nest. Covered in this way the nest looks like a heap of fresh and putrefied pieces of water plants piled up by the wind and waves. TEMPERATURE OF THE NEST It is well-known to field observers that the nests of grebes are especially warm in the last stage of incubation. I measured the temperature in 14 nests of Black-necked Grebes in a colony on a fish-pond during the second half of June The incubation period was coming to an end and the young ones were just beginning to hatch in a few of the nests. Three measurements of temperature were taken in each nest. (1) Deep down in the mass of material beneath the surface of water; (2) at the bottom of the nest cup just under the eggs; (3) in the layer of nest material used by the brooding bird to cover the eggs before leaving (Fig. I). I measured the temperatures after thermometers had been left in each of these three places for ten minutes and these are given in Table III. The temperature in the mass of the nest material was constant and similar in all the nests examined but it was higher than the temperature of the surrounding water by 1 C or more. The temperature immediately under the eggs ranged from 22.2 C to 28.0 C. The greatest differences were found in the temperature of the material used to cover the eggs. This depends on the air temperature and especially on the solar radiation received by the nest. This is best illustrated by the data from nest 1 (Table III). The temperature in this nest was first recorded as 28.9 C in the sun, dropped to 25.2 C after ten minutes in the shade, and to 23.6 C after a further ten minutes. This shows that the initial temperature was closely connected with the intensive insolation of the nest. 8

5 GREBE NESTING BIOLOGY TABLE III-MEASUREMENTS OF TEMPERATURE IN NESTS CC) Ser. no. Temp. Temp. Temp. of Air Water Date-hour in the under covering temp. temp. weather depth eggs layer Notes of nest after Io min. in shade 25.2 and 23.6 after 20 min. in shade sunny ca II rain at night, drizzle till , then cloudy What is the reason for these high temperatures in :I grebe's nest? This problem has interested ornithologists for many years. Some believe that the nest temperature is higher than that of the environment because of the heat generated from putrefaction and this is the view advanced by Hall (1942) amongst others. Some German authors (Heinroth, 1928; Niethammer, 1942; Oldberg, 1952) hold the view that this hypothesis has been disproved by Schiermann (1927) who carried out investigations on the nests of Great Crested Grebes (Podiceps cristatus). According to his conclusions, the nest temperatures of grebes are no higher than those of other water birds (Coot (Fulica atra), Common Pochard (Aythya ferina) and Moorhen), nor can it be established that heat is generated by the putrefying plant material. On the other hand, the layer of nest material used for covering the eggs is obviously a good heat insulator. The conclusion of Hanzák (1952) is similar to that of Schiermann and he also excludes any influence of the decay of nest material, assuming that all the heat accumulated in the nest is derived from the brooding bird's body. COMMENTS ON RESULTS The fact that the highest temperature of a grebe's nest was that taken immediately after the brooding birds had left, shows that heat is given to the nest by the brooding birds, and is an important positive component of the general heat equation of the nest. There may be, however, other sources of heat in the nests of grebes. The role of solar energy is of some importance here as the following argument suggests. Nest material soaked in water is a good conductor of heat and consequently it warms up fast. It is mostly dark in colour and, 9

6 BIRD STUDY therefore, it absorbs solar radiation. On hot days the incubating birds very often leave the nest for long periods merely covering the clutch (Dementiev, 1951). This is not only done to protect the eggs against birds of prey, as most authors emphasise, or to prevent a heat loss, as Schiermann believes, but also to accumulate the heat from solar radiation on hot, sunny days. The covering layer can do this task as long as it is exposed to the sunshine. After sunset it cools very fast (cf. Table III). The measurements given in Table III were taken in a colony of Blacknecked Grebes during two and a half hours on each of two days. During this time the birds were too alarmed to sit on the eggs, but nevertheless the nests did not cool completely. This is significant considering the good conduction of heat by the nest material, which should have resulted in a rapid loss of heat. The temperature drop in the layer covering the eggs is an example of this (Table III). In this way the nests of grebes contrast with the nests of most water birds which are built of dry material and which remain so throughout incubation; thus they are bad conductors of heat. The fact that the grebe's nest does not rapidly cool down indicates that heat is generated by the rotting vegetable material, especially that in the lower nest layers lying under water. Observations on recently built nests at the beginning of incubation show that they cool faster than in the final stages of incubation. This suggests an increase of the heat generated in the putrefying vegetable material as the course of incubation progresses and may be associated with the inter-dependence between the intensity of putrefaction and the temperature. At the beginning of incubation the bird warms the nest with the heat of its body. Thereby it may bring about an intensification of decay and so increase the generation of heat. Owing to the production of heat in the nest the process of cooling slows down as the incubation proceeds. The rise of the nest temperature in the course of incubation is clearly shown in Table IV and Fig. 2. This table has been constructed from the data given by Schiermann on temperature measurements in the nests of Great Crested Grebes. The entries are arranged according to the days of incubation. The differences between the nest temperature and the temperature of the surrounding water have been calculated to show that the increase of the former was independent of the latter (Fig. 3). Both the nest temperature and the difference between it and the water temperature increase as incubation progresses in spite of the fact that the water temperature in the vicinity of the nest does not show any tendency to rise but oscillates within steady limits. This points to an increase of the heat content of the nest, and therefore, in the heat equation, there is an increase in the gains in relation to the uniform losses owing to radiation into the environment. If we add that the temperature of a bird's body does not rise during the course of incubation (Dementiev, 1940) nor does the intensity of incubation increase, then it seems that the sources of the temperature rise must be looked for in the fermentation process of the nest material. Schiermann IO

7 GREBE NESTING BIOLOGY ` 17' 15 ^. 7 ^ ^ ^ ^ ^b 7 N,. r b *"... R / \ ^ i '^\. / b ^ g ' ^ /. r 2l r \ r \ r Days FIGURE z. Diagram showing the increase of temperature in the nest of the Great Crested Grebe during the process of incubation (according to Schiermann's data in Table IV). The solid line shows the average temperatures of the nest material under the eggs, and the dashed line the temperature of the material under the surface of the water. rejected the possibility that the heat generated during the decay of nest material might take part in the general heat equation of the nest for the following reasons. I. If the nest had been producing its own heat, the nests left by the brooding birds would have remained at a level temperature, but this was not observed by the author. 2. He noticed only a slight rise of temperature in an artificial nest made of the same material as natural nests and this rise was followed by cooling, which seemed to indicate that the amount of heat generated here was negligible. 3. Observations on the nest of a Little Grebe (Podiceps ruficollis) showed that in the absence of the birds it cooled almost to the temperature of the environment. 4. Measurements of nest size and temperature showed no correlation such as should have existed if heat was a function of decay, since the quantity of heat should be proportional to the quantity of material in which it is generated. 5. Temperatures in the nests of other water birds did not differ from those in the nests of grebes. I I

8 BIRD STUDY TABLE IV-MEASUREMENTS OF TEMPERATURE ( C1 IN NESTS (FROM SCHIERMANN, 1927) OF GREAT CRESTED GREBE Q-_ v 8á ^.. 0 '.'t',.5, O 2tV -r.4.2, ^ bp ' Q ^ r Q^ 2, '''c, -9' d y y0q Oi Q ` Y V^ r` +.V. `,t s k^ Er< ^ ^^ o^ Z 1 y o^ Q + ' ~. v a, d Q y E R, N t' ^ h og ^ v s ^ 2H ^h y ^C ^ eo 3 Q. ia : i ó N ^ v Z": ^ ^ S. S' Q z6.o 23.0 I I o I.O I III.7 8.o 3.o o 23.0 II.I' II.2' 2.5 ( V.7' 9.0 J III.Io o 6.o III.2" I.4 I I o III.I" o 22.5 III II.4' o II.5' 8.o IVIO' 9.o III.I I IV.1" 13.0 IO.I IV.2"' IV.12' III.S" 8.o 8.o 6.o 6.o o 23.0 I II.3' IV.S"' ^ 12.5 IO.o 7.0 } IO III.3" IV.3"' 8.o 8.o o o III o 9.o o IV.9' III o 26.5 IV.8' II.o 11.0 In my opinion these facts do not refute the idea that the heat of putrefaction plays a part in the general heat-equation of the nest for the following reasons. I. The fact, questioned by Schiermann, that temperatures in a cooling nest stabilize at C, especially in the nests at an advanced stage of incubation, can be demonstrated. This is shown by a greater stability of Oi 8= ^ Y ^ ^^ I2

9 15 13 II 9 p...0.'" O o^` i b ^. ^ 7.` ^` o p^d P, d I / 5 ;/ s d 3 GREBE NESTING BIOLOGY temperature in the depth of a nest (cf. Table III) and by the actual measurements, taken by Schiermann, which show that a temperature of C persists for a long time with hardly any decrease. 2. The artificial nest was not warmed to the temperature of a brooding bird and so the process of putrefaction was not intense. 3. The nest of a Little Grebe cooled down to i8 C (the water temperature being 16.5 C), since it was in the first stage of incubation and the process of decay was not well advanced. 4. It is a well-known phenomenon in the biology of the Great Crested Grebe that this bird completes the building of its nest during incubation, so that at the end of this period the nest not unfrequently attains a remarkable size (Hanzak, 1952). The growth of the nest mass as an element generating heat results in a rise of temperature shown in the diagram (Fig. 2). The quantity of material used to build the nest varies rather remarkably with different pairs of grebes and, therefore, to show the dependence of nest temperature upon the growth of the nest mass, one must base conclusions on the observations made during the whole period of incubation. 5. Schiermann's last argument is not relevant, considering the differences in nest materials of grebes and of other water birds and the consequent variation in heat conductivity., ^ ^ Days FIGURE 3. Diagram showing the increase of differences between the temperatures of nest material and those of the water surrounding the nest during the process of incubation (according to Shiermann's data in Table IV). The solid line shows the increase of differences between the temperatures in the layer of material immediately under the eggs and those of the water ; the dashed line the same between the temperatures in the material under the surface of the water and the temperature of the water. 1 3

10 BIRD STUDY Hanzak (1952) also doubted the importance of putrefaction in the heatequation of grebes' nests. He based his assumption on the facts that the temperature at the bottom of the nests of these birds was lower at least by 1 C than the temperature of the eggs, and that a number of nests lacked decaying material. It is probable that he was dealing with nests at an early stage of incubation and because of that he failed to find a putrefaction process in them. The fact that the bottom of a grebe's nest is somewhat cooler than the eggs warmed by the brooding bird does not contradict the importance of heat derived from putreying material for the incubation process. This heating effect takes place in spite of the fact that grebes belong to a group of birds which has the lowest body temperature and consequently a comparatively low temperature of incubation (Wing, 1956). The heat of putrefaction in grebes' nests is too low to hatch the eggs by itself and that is why the birds have to warm the eggs with their own bodies. In the case of the Megapodidae (mound builders) the nest temperature resulting from the rotting of vegetable material is so high that the birds need not sit on the eggs themselves. In grebes, heat provided by putrefaction may protect the nest and eggs against the rapid fall of temperature after it has been left by the brooding bird, especially at an advanced stage of incubation. The greater the heat generation, the longer the time necessary for the nest to cool completely. Summing up the results of the present study, it may be concluded that in the heat-equation of grebes' nests, the positive part is derived (1) from the body heat of the brooding birds, (2) from the heat of solar radiation accumulated in the external layer of nest material and (3) from the heat generated in the putrefying material of the nest. The first two factors contribute directly to the process of incubation, while the third one contributes to it indirectly by preventing the nests from rapid cooling while they are unattended. It may be of biological importance on cloudy and cool days, especially at an advanced stage of incubation. SUMMARY It has been shown from a series of measurements that the dimensions of the nest of Black-necked Grebes are very variable. This is connected with the great plasticity of nest material. The inner diameter of the nest cup is proportional to the number of eggs in the clutch. The measurements of temperature in the nests show that in the heat equation of a nest, a positive part is contributed by the heat of the incubating bird, the solar heat accumulated in the layer covering the eggs and the heat derived from the putrefying nest material. The last acts only indirectly by slowing down the cooling of the nest. ACKNOWLEDGEMENTS I owe a debt of thanks to Prof. R. J. Wojtusiak, Head of the Department of Animal Psychology, Jagiellonian University, for his valuable suggestions during my work on this subject. I also wish to thank Prof. K. Starmach, Head of the Laboratory of 14

11 GREBE NESTING BIOLOGY Water Biology, Polish Academy of Science, and Mr. J. Wiltowski for enabling me to gather materials necessary for this study on the fish-ponds in the Experimental Fish Farm at Golysz. REFERENCES BOCHENSKI, z Observations on the location and construction of nests of the Spotted Flycatcher, Muscicapa striata (Pall.) Zeszyty Nauk. Uniw. Jagiell. Zoologia, 2 :77-83 (Polish with English summary). DEMENTIEV, G. P The Guide to Zoology. Vol. VI: Birds, Moscow & Leningrad (in Russian). DEMENTIEV, G. P The Birds of the Soviet Union, vol. II. Moscow (in Russian). HALL, C. A A Pocket-Book of British Birds' Eggs and Nests, London. HEINROTH, 0. & M Die Vogel Mittleuropas, Vol. III. Berlin. HANZAR, I The Great Crested Grebe, Podiceps c. cristatus (L.), its ecology and economic significance. Acta. Mus. Nat. Pragae, 8 B (1952) no. 1 Zoologia Praha. NIETHAMMER, G Han dbuch der Deutschen Vogelkunde, 2 : Leipzig. OLDBERG, G Vogel im Schilf. Leipzig. PROMPTOV, A. N Physiological analysis of the nest building instinct in birds. Bull. Acad. Sci. USSR. Biol. Ser Moscow (Russian with English summary). SCHIERMANN, G Untersuchungen an Nestern des Haubentauchers, Podiceps cristatus. J. Orn. Lpz. 75: WING, L. W Natural History of Birds. A Guide to Ornithology, New York. Notes on the chicks of the Little Ringed Plover By J. Walters Received 26 February 196o FLEDGING PERIOD UNTIL 1 958, it was generally stated that young Little Ringed Plovers (Charadrius dubius) become fledged about days after hatching. Several sources give the fledging period, e.g. Heinroth (1928) 21 days (in confinement); Dathe and Miller (1932) days (7-28 June and 8-3o July); Kriische (1936) 21 days; Witherby a al (1947) days. In 1958, two papers appeared mentioning considerably longer periods, viz. Bub (1958) (one case of 32 days) and Stein (1958), who established for one brood of four young, a fledging period longer than 26 days. Although not established in the most exact way, both data nevertheless give rise to doubt of the general validity of the period of days. I had an opportunity in 1959, near Amsterdam, to follow five Little Ringed Plover chicks from hatching until their first flight. In all cases the birds were considered to have fledged when they could avoid capture by flying. Of course, the presence of danger could have advanced the moment of the first flight, though certainly not considerably. I have 15