Svein Haftorn

Different metabolic strategies of northern birds for nocturnal survival

Summary1.The regulation of O2-consumption and body temperature, especially the occurrence and utilization of nocturnal hypothermia, was studied in three small-sized northern species of birds occupying different ecological niches. Being sympatric, the Willow titParus montanus, the Great titP. major and the Common redpollAcanthis flammea encounter the same environmental conditions during the winter-time, i.e. long nights, low ambient temperatures, a snow-cover, and the possibility of periods of food shortage.2.When fed ad libitum, neither the Great tit nor the Common redpoll utilized nocturnal hypothermia. The Willow tit lowered the body temperature to a value which was significantly correlated with that of the ambient temperature.3.During fasting experiments the evening body weights of the birds were depleted 10–20% below the normal value. In all three bird species the O2-consumption during the night was positively correlated to the body weight of the birds. Consequently, the depth of hypothermia achieved at thermal homeostasis was inversely correlated to body weight.4.When energy reserves in terms of body weight, are less than normal, both Willow tit, Great tit and Common redpoll utilize nocturnal hypothermia in order to make the energy reserves last throughout the night. The reason why the latter two species, in contrast to the Willow tit, do not use nocturnal hypothermia under normal conditions, may be due to differences in body size and also feeding strategies.

Nocturnal hypothermia and metabolism in the Willow TitParus montanus at 63° N

Summary1.The dynamics of temperature regulation on a diurnal and annual basis were studied in seasonally acclimatized Willow Tits. The diurnal thermoregulation pattern of the tits was the same at all seasons of the year, i.e. at roosting time the body temperature gradually fell until it levelled off at some time between 2100 and 2200h. Then the body temperature remained more or less constant until two to three hours before sunrise, when it gradually rose to the normal daytime level by the start of the daytime activity period (Fig. 1 and 3 A-B).2.Body temperature and O2-consumption rates were recorded on winter acclimatized Willow Tits, exposed to a series of different but constant ambient temperatures during night. The values at which the body temperature levelled off at night was significantly correlated with that of the ambient temperature (Fig. 2). Energy expenditure on an overnight basis was lowered considerably when the tits entered nocturnal hypothermia (Fig. 5).3.The Willow Tits showed a marked seasonal variation with regard to the depth of hypothermia achieved when they were exposed to different ambient temperatures. The maximum response was observed in mid-winter acclimatized birds, whereas mid-summer acclimatized birds showed almost no response. Between these two extremes, a steady gradient was found (Fig. 4).4.The observed nocturnal hypothermia was a controlled physiological response to low ambient temperature and long winter nights. All the birds in the experiment arose to the normal diurnal body temperature in the morning.

The diurnal body weight cycle in titmice Parus spp.

The diurnal weight cycle of five species of tits (Parus montanus, P. palustris, P. major, P. caeruleus and P. ater) was studied in Norway. The daily weight increase (DWI) tended to rise to a maximum in mid-winter and thereafter decline. The hourly weight increase (HWI) showed a marked seasonal fluctuation and was about twice as high in mid-winter as in autumn and spring. Generally HWI was highest in the morning, but tended to vary with rank order during mid-winter, i. e. being highest in the dominants. A relatively high evening weight was followed by a large nightly weight decrease, and vice versa. Thus the nightly metabolism seems to be adjusted according to the evening weight, as previously shown in captive Willow Tits. It is suggested that hypothermia during sleep is a trade-off between energy reserves and predation risk. The air temperature apparently had only a negligible effect on the weight fluctuations, perhaps because of the relatively mild winters during the study period.

CONTEXTS AND POSSIBLE FUNCTIONS OF ALARM CALLING IN THE WILLOW TIT, PARUS MONTANUS; THE PRINCIPLE OF ‘BETTER SAFE THAN SORRY’

The primary alarm call in the willow tit consists of a series of high-pitched, short zi (zee) notes. A large variety of birds flying overhead may evoke alarm calls in the willow tit, many of which are quite harmless to the species. Also many types of ‘disturbances’ in the forest may elicit alarm calls, including sudden appearance of humans. Alarm calling seems to be an altruistic event since the caller puts itself into a dangerous situation by attracting the predator’s attention, while leaving time for associates to take relevant precautions. For an evolutionary selection of alarm calling the cost involved must somehow be outweighed by factor(s) beneficial to the caller. Among several hypotheses trying to explain possible functions of alarm calls, warning of kin and mates seems most likely with regard to tits. The relevance of the ‘food resource usurpation-hypothesis’ needs further study under natural conditions. The high proportion of ‘false’ alarms is remarkable. A strategy of ‘better safe than sorry’ seems to be advantageous, because the time left for appropriate precautions in case of a real attack is so marginal that it pays in the long run to react to any possible threat even if it turns out to be harmless.

The effect of short-time fasting on metabolism and nocturnal hypothermia in the Willow TitParus montanus

Summary1.The effect of body weight on O2-consumption rate and nocturnal hypothermia was studied in winter acclimatized Willow TitsParus montanus.2.During the fasting experiments, the birds were kept at a constant ambient temperature of 0°C, and a photoperiod of 8L: 16D. O2-consumption rate and deep body temperature were recorded continuously throughout the night. The O2-consumption rate during the night was positively correlated to the body weight of the birds. Consequently, the depth of hypothermia achieved at thermal homeostasis was inversely correlated to the body weight.3.The results obtained indicate that depending on season, ambient temperature and energy reserves, the Willow Tit regulates its metabolic rate so as to keep it at a level which corresponds fairly well to the maximum affordable energy expenditure.

Clutch size, intraclutch egg size variation, and breeding strategy in the GoldcrestRegulus regulus

In Fennoscandia the Goldcrest regularly lays two clutches per breeding season. Near Trondheim in Central Norway (about 63° N) the mean size of 11 first clutches was 10.4 (9–12) eggs and of 10 second/repeat clutches 9.4 (8–11) eggs. Mean egg length was 13.49 mm, breadth 10.35 mm, mean weight of freshly-laid eggs 0.78 g, volume 737 mm3 and shape index 130.6. The correlation coefficient for egg length against weight was 0.47, and for egg breadth against weight 0.77. For the four clutches studied in more detail, all egg dimensions, except the shape index, increased with the laying sequence. On average, the last-laid egg was 20.1 % heavier than the first-laid egg, or 5.6 % heavier than the mean weight for the whole clutch. The 3–5 last-laid eggs in the clutch deviated by about the same magnitude from the clutch mean. Because of the pronounced asynchrony in hatching, the size-hierarchy within a Goldcrest brood may be considerable, at least 1:5. The survival chances of the smallest young in a brood apparently depend mainly on the prevailing food supply. The primary advantage of hatching from a relatively large-sized egg is probably that such a hatchling is strong enough to secure itself a favourable feeding position in the crowded nest, in which the young often form 2–3 horizontal layers. The parental selection of food is adjusted to the size of the young, even in a brood with a marked size-hierarchy. It is concluded that the Goldcrest has evolved a brood reduction strategy. In Fennoskandien zeitigt das Wintergoldhähnchen regelmäßig zwei Gelege pro Brutsaison. In einem Kontrollgebiet bei Trondheim in Mittelnorwegen (ca. 63° N) betrug die mittlere Gelegegröße für 11 Erstgelege 10,4 (9–12) und für 10 Zweit- bzw. Ersatzgelege 9,4 (8–11) Eier. Die mittlere Eilänge betrug 13,5 mm, die Eibreite 10,35 mm, das mittlere Frischvollgewicht 0,78 g; das Volumen maß 737 mm3, der Eiformindex (=Länge/Breite × 100) 130,6. Die Korrelation zwischen Länge und Gewicht betrug 0,47, zwischen Breite und Gewicht 0,77. Bei vier genauer untersuchten Gelegen nahmen alle Eidimensionen mit Ausnahme des Eiformindex mit der Legefolge zu. Im Mittel war das letzte Ei 20,1 % schwerer als das erste oder 5,6 % schwerer als das mittlere Gewicht des gesamten Geleges; letzteres gilt auch für die 3 bis 5 zuletzt gelegten Eier. Als Folge des bemerkenswert asynchronen Schlupfes sind die Größenunterschiede innerhalb einer Goldhähnchenbrut beachtlich, nämlich mindestens 1:5. Die Überlebenschancen des kleinsten Jungen einer Brut hängen offensichtlich vor allem vom Nahrungsangebot ab. Der primäre Vorteil eines Jungen aus einem großen Ei liegt möglicherweise darin, daß dieser Nestling stark genug ist, um sich eine günstige Position im dichtbesetzten Nest bei den Fütterungen zu sichern. Die Jungen liegen oft in zwei bis drei Schichten übereinander. Die Nahrungswahl der Altvögel richtet sich nach der Jungengröße, sogar in einer Brut mit deutlichen Größenunterschieden. Das Wintergoldhähnchen hat wahrscheinlich die Strategie einer Brutreduzierung in Anpassung an knappes Nahrungsangebot entwickelt.

Is the Coal Tit Parus ater Really the Most Subordinate of the Scandinavian Tits

were usually successful in their supplanting attacks, but the dominance order between the two species was not absolute and the number of interspecific interactions were few. As emphasised by the authors, it is necessary to consider how applicable the results from birds held in captivity are to the natural situation. In this paper I present the results of interspecific encounters between five tit species visiting an outdoor feeder in central Norway. In general, the following social rank order was observed: Great Tit P. major > Blue Tit P. caeruleus > Marsh Tit P. palustris > Coal Tit > Willow Tit. The Coal Tits showed a statistically significant tendency to be dominant over the larger Willow Tits, although not in all cases. Nevertheless, it seems that the Coal Tits status in the social hierarchy requires consideration in the current discussion on the interspecific competition for food and foraging sites among species belonging to the tit guild of the coniferous forest.

Thermoregulatory abilities in chicks of the Antarctic Petrel (Thalassoica antarctica)

SummaryWe studied the thermoregulatory capacity of Antarctic Petrel chicks, Thalassoica antarctica, breeding in a large colony in Queen Maud Land (71°53′S,5°10′E) on the Antarctic continent. Compared to newly hatched chicks of other birds, those of the Antarctic Petrel are characterized by a relatively high standard metabolic rate (SMR) and thermal conductance. Their metabolic scope is limited, however, being only 1.6 times the SMR, and they consequently depend on parental brooding to maintain Tb. At an age of 11 days the chicks become thermally independent and are left alone in the nest. The chicks keep a relatively high body temperature (>36°C) throughout their early development and we found no indication that they normally experience hypothermia. A significant positive relationship between latitude of breeding and SMR of the hatchlings is shown to exist for procellariiform birds. It is suggested that the high SMR found in Antarctic Petrel hatchlings could be a prerequisite for achieving a high growth rate, rather than being of any thermoregulatory significance.

Egg-Laying Behavior in Tits

Like most passerines, tits lay their eggs early in the morning. Traditionally, ornithologists determine laying times indirectly by checking the nest content at different times of the day. Only a few persons seem to have actually witnessed the egg-laying itself. Haftorn (1966) gave a preliminary description in Norwegian of egg-laying behavior in tits. Subsequently, Flanagan and Morris (1975) published photos of a female Blue Tit (Parus caeruleus) during egg-laying. Over the years I have observed egg-laying in many females of several tit species and am therefore able to give a more comprehensive quantitative description of this phenome-

Thermoregulatory and behavioral responses during incubation of free-living female Pied Flycatchers Ficedula hypoleuca

The changes in body temperature (Tb), respiratory frequency (fR) and oxygen consumption (M) of two free-living Pied Flycatcher females were recorded during the incubation period. Tb followed a marked diurnal rhythm, with maximum temperatures around noon or just afterwards and minimum temperatures during the night. Upon entering the nest Tb decreased (phase 1) to a minimum level (phase 2) and then increased (phase 3) prior to the females next period-off. Phases 1-2 and part of phase 3 coincided with the warming up of the eggs to an incubation temperature of approx. 35-370C. The duration of the females periods-on was negatively related to the egg temperature at the start of incubation and positively to the metabolic rate. Respiratory frequency was high at the onset of the periods-on, declined thereafter, and finally levelled off; fR tended to increase again shortly before the female left the nest. Experimental maintenance of the eggs at incubation temperature during the females periods-off resulted in an immediate increase in Tb when she resettled on the eggs, and a marked shortening of the periods-on. Conversely, when the eggs instead were cooled down during the females periods-off, the following periods-on were considerably lengthened and M correspondingly increased.