Energetics of the acrobatic courtship in male golden-collared manakins (Manacus vitellinus)

Abstract

In lek mating systems, females choose mates through indicators of quality, which males may exhibit by their performance of courtship displays. In temperate regions, displaying seasons are brief (one to two months), whereas in the tropics courtship seasons may be prolonged. Moreover, in temperate-breeding animals lekking behaviour can be energetically demanding, but little is known about the energy costs of lekking in tropical animals. Daily, over the course of a nearly seven-month-long breeding season, male golden-collared manakins (Manacus vitellinus) of Panamanian rainforests perform acrobatic courtship displays that markedly elevate heart rates, suggesting that they require high energy investment. Typically, animals of tropical lowland forests (such as manakins) exhibit a 'slow pace of life' metabolic strategy. We investigated whether male manakin courtship is indeed metabolically costly or whether the birds retain a low daily energy expenditure (DEE), as seen in other tropical species. To assess these questions, we calibrated manakin heart rate against metabolic rate, examined daily lek activity and, using telemetry, obtained heart rates of individual wild, lekking male manakins. Although metabolic rates peak during courtship displays, we found that males actually invest minimal time (only approx. 5 min d(-1)) performing displays. As a consequence, the DEE of approximately 39 kJ d(-1) for male manakins is comparable to other lowland tropical species. The short, intense bursts of courtship by these birds make up only approximately 1.2% of their total DEE. Presumably, this cost is negligible, enabling them to perform daily at their arenas for months on end.

Keywords: courtship; energetics; heart rate telemetry; manakins; tropics.

Figure 1.

Diurnal pattern of courtship activity of male GC manakins. Mechanically produced sounds (wingsnaps and rollsnaps), measures of manakin social and courtship behaviour at the lek, were recorded for five different leks in three 1-day recordings. Hourly means were calculated including 30 min before and after the time point. Values were then divided by the number of males (4±1) on the corresponding lek, which was determined with direct behavioural observations. Mean values of sounds produced male⁻¹ h⁻¹ on each of the five leks are shown.

Figure 2.

Hourly differences in activity and heart rate levels. Results of Bonferroni-corrected post hoc tests comparing activity and heart rate levels between different hours of the day (07.00 to 17.00). Arrows indicate significant differences. The shaded area shows values for heart rates and arrows refer to the hours on the top. For example, heart rate is lower at 13.00 compared with 08.00. The non-shaded area of the table refers to activity and arrows refer to hours on the left. An example is the significantly lower activity at 17.00 compared with 07.00 and 08.00.

Figure 3.

Daily heart rate pattern. The thick line represents the hourly mean heart rates of eight male GC manakins. Hourly averages were calculated for the 30 min before and after the time point. During the night, we obtained heart rate measurements of only six manakins. No measure was taken at 3.00 in the morning, thus we averaged values of 2.00 and 4.00 to complete the graph. Thin lines represent the 95% CIs (1 s.d.). Shaded areas indicate night time (18.12 until 06.15).

Figure 4.

Relationship between heart rates and metabolic rates. Least-square regressions of heart rates against metabolic rates for four birds determined by calibration measurements: bird E (p < 0.001), bird G (p = 0.013), bird H (p < 0.001) and bird I (p < 0.001). See table 1 for statistical details.