The natural plasma testosterone profile of male blue tits during the breeding season and its relation to song output

In male birds, the gonadal hormone testosterone (T) is known to influence territorial and mating behaviour. Plasma levels of T show seasonal fluctuations which vary in relation to mating system and social instability. First, we determined the natural T profile of male blue tits Parus caeruleus during the breeding season. We found that plasma levels of T increased at the onset of nest building. Thus, the increase in circulating T was not associated with territory establishment, nor with the fertile period of the males' mates. In most individuals, T levels dropped to values close to zero during the period of chick feeding. Second, we investigated the relationship between plasma levels of T and male age, size, and singing behaviour. During the mating period, T levels did not differ between 1 yr old and older males and did not correlate with body size or condition. However, song output during the dawn chorus tended to be positively correlated with T levels. Therefore, if high T levels are costly, song output might be an honest indicator of male quality in blue tits. Finally, we show that plasma levels of T are significantly higher during the night than during the day. This pattern has also been observed in captive non-passerine birds, but its functional significance remains unknown.

Season and outdoor ambient temperature: Effects on birth weight

Objective: To determine the extent to which meteorologic factors explain seasonality in birth weight in a developed country.

Basking is affected by season and influences oxygen consumption in desert-living striped mice

Small mammals that inhabit arid and temporally unproductive environments use several methods to conserve energy. Here, we investigate the energetic role of sun basking in striped mice Rhabdomys pumilio from the Succulent Karoo desert in South Africa. We observed mice in front of their nests for 140 h and recorded the time they spent basking during the non-breeding (dry) and the breeding (wet) seasons. We measured temperature changes in model mice to provide an indication of the heat that can be absorbed from the sun. Finally, we measured the oxygen consumption (circle dot O-2) of mice at their basking sites in the field both in the sun and in the shade. This was accomplished using a portable respirometry system with a metabolism chamber, which could be placed in and out of the sun. Observations showed that mice basked more often during the non-breeding than during the breeding season. During the former season, mice spent an average of 11.9 +/- 1.1 min (se) in the morning and 5.5 +/- 0.5 min in the afternoon per day basking. Within the metabolism chamber, circle dot O-2 decreased when the animal was in the sunshine compared with the shade. This effect occurred independent of the ambient temperature (T-a), indicating that a significant amount of radiant energy was absorbed from the sun. Basking may be an alternative to other energy-acquisition behaviours, such as foraging, which might be particularly useful at times when food is scarce.

Preliminary Report of the 1 field season at Gubbio.:Malone, C.A.T. and S.K.F. Stoddart,

Xerox circulation to sponsors. Cambridge University.

Preliminary report of the 1984 field season at Gubbio.,

Malone, C.A.T., et al., in Xerox circulation to sponsors. 1984. Cambridge University.

Provisional report. 1986 Season. Gubbio Project.

Stoddart, S.K.F. and C. Malone, ProXerox circulation to sponsors. 1986.

Provisional report. 1987 Season. Gubbio Project

Stoddart, S.K.F. and C. Malone,. Xerox circulation to sponsors. 1987.

1988 Season. Cambridge Gozo Project.

Stoddart, S.K.F.M., C and Trump. D, Provisional report. Xerox circulation to sponsors. 1988.

Provisional report. 1990 Season. Gozo Project.

Malone, C.A.T. and S.K.F. Stoddart, 1990. Cambridge

Provisional Report of the 1994 season of the Gozo Project.

Stoddart, S. and C. Malone, PPrivate Circulation to sponsors. 1994.

Provisional Report of the 1996 season of the Gozo Project.

Stoddart, S. and C. Malone, Private Circulation to sponsors. 1996.

Short report on the 1997 field survey season of the Troina project.

Stoddart, S. and M. C, Private circulation to sponsors. 1997.