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Over the past decade, the fields of ecology and evolutionary biology have begun to explore the causes and consequences of telomere length variation, but, unfortunately, measuring telomeres is complicated. This has naturally resulted in a progression of new methodologies, as they are adopted, refined, and are sometimes discarded when better tools become available. Recent papers have alerted ecologists to potential methodological problems, and called for standardization in telomere measurement and analysis methodologies (Haussmann and Mauck, 2008; Monaghan, 2010). The recent review of current methodology by Horn et al. (2010) again emphasizes where caution is needed when measuring telomeres.

1. We investigated the relationship between hatching date and fledging success in the European coot (Fulica atra).2. The production of fledglings per brood increased in the first half of the season and decreased in the second half, independent of clutch size or egg size. We tested experimentally whether this convex seasonal pattern is causally related to date.3. The timing of parental care was manipulated by exchanging complete first clutches that differed in stage of incubation. Our experiments tested whether the natural variation in fledging success was due to (i) factors related to date (date hypothesis), (ii) factors related to parental and/or territory quality (parental quality hypothesis), or to a combination of both factors.4. In the first half of the season, an experimental advance of the timing of parental care reduced fledging success, while an experimental delay raised it. In the second half of the season the opposite was found. Fledgling production by experimental pairs did not differ systematically from that of control pairs raising young at the same time.5. Thus, the results were consistent only with the date hypothesis, and we conclude that timing of breeding and fledging success are causally related in the coot.6. Independent of date, age of male parents was positively correlated with fledging success, suggesting that aspects of parental quality play an additional role.

(1) We investigated experimentally whether timing of reproduction is causally involved in the seasonal decline in reproductive success in the great tit Parus m. major L. This is important because of its implications for the optimization of reproductive decisions of the individual bird.(2) Timing of breeding was manipulated by inducing repeat clutches through removal of the first clutch. The experiment was performed in 1987 in two forests (W and O) and followed up the year after. It was assumed that parental quality was unaffected by the experiment. Reproductive success of the experimental and undisturbed control clutches was compared. For forest O, reproductive success of the experimental clutches was also compared with the expected reproductive success of first clutches laid at the same time.(3) Clutch size, fledging success and nestling weight in experimental clutches were reduced as compared with controls in forest W but not in forest O. We conclude that late breeding causes reduced pre-fledging reproductive success in forest W but not in forest O.(4) Recruitment of fledged young in the breeding population was strongly reduced by the experiment. We conclude that late breeding caused reduced post-fledging reproductive success in both forests.(5) Survival of females was reduced by the experiment in forest O relative to controls and this corresponded with the natural seasonal trend. Survival of females in W and of males in both forests was unaffected. In experimental females, clutch size in the next breeding season was reduced by 1.6 eggs compared with controls. The clutch size of the males was unaffected, as was the following year's laying date for both sexes. We conclude that future reproductive success of females, but not of males, is also related to the timing of current reproduction.(6) Possible mechanisms underlying the relationship between date and reproductive success are discussed. It is suggested that differences in pre-fledging reproductive success induced by the experiment are related to food availability. Differences in post-fledging reproductive success are probably caused by competition between early and late young.

The relationship between body size and basal metabolic rate (BMR) in homeo therms has been treated in the literature primarily by comparison between species of mammals or birds. This paper focuses on the intraindividual changes in BMR when body mass (W) varies with different maintenance regimens. BMR varied in individual kestrels in proportion to W1.67, which is considerably steeper than the mass exponents for homomorphic change (0.667; Heusner, 1984) for interspecific comparison among all birds (0.677) or raptors (0.678), for interindividual comparison of kestrels on ad libitum maintenance regimens (0.786), and for mass proportionality (1.00). The circadian range of telemetered core temperature also varied more strongly with intraindividual than with interspecific (Aschoff, 1981a) variation in mass. This was due to reduced nocturnal core temperature at low-maintenance regimens, which was, however, insufficient to account for the excessive reduction in BMR. Carcass analysis of eight birds sacrificed revealed a disproportionate reduction in heart and kidney lean mass at low-maintenance regimens. We surmise that variation in BMR primarily reflects variation in these metabolically highly active tissues. This may account for positive correlations found between heart, kidney, and BMR residuals relative to interspecific allometric prediction, and between α and p residuals, as expected on the basis of the constant excess of BMR during α above BMR during p (Aschoff & Pohl, 1970a).

SUMMARY Food availability is a key factor in ecology and evolution, but available techniques to manipulate the effort to acquire food in vertebrates are technically challenging and/or labour intensive. We present a simple technique to increase foraging costs in seed-eating birds that can be applied with little effort and at low monetary cost for prolonged periods (years) to solitary or group-housed animals. The essence of the technique is that food is offered in a container above ground level, with holes in the sides from which the food can be taken, forcing birds into energetically demanding hovering flight to forage. As a control treatment we offered a similar container but with perches mounted beneath the holes, allowing birds to eat without extra flights. Increasing foraging costs in this way induced zebra finches to double the time spent foraging, and to decrease their basal metabolic rate, in agreement with results obtained using more laborious techniques to increase foraging costs. The technique was not too severe because mortality was low during a winter with sub-zero temperatures. As foraging costs under natural conditions are generally higher than those under standard laboratory conditions, we suggest that measuring behaviour and physiology when animals have to work for food may better reflect their natural state.

We experimentally reduced clutch size of Great Tits Parus major to investigate the effects on parental care (including Daily Energy Expenditure, DEE, measured with doubly labelled water), and the relationship between DEE and the residual reproductive Value. The length of a working day was not affected, but the nestling phase was 0.7 days (4%) shorter in experimental clutches. Males fed reduced broods at a lower rate, but DEE and mass (loss) were not significantly affected by the experiment. However, male DEE was positively correlated with feeding frequency, and this relationship did not differ between control and experimental males. This suggests that the experiment resulted in a slight reduction in male DEE, and lack of statistical significance can be attributed to the power of the test applied. Females fed reduced broods at a lower rate, but female DEE and mass (loss) were not affected by the clutch size manipulation. Female DEE was not correlated with feeding frequency, the original number of eggs in the nest or the actual number of young. The division of labour (feeding rate, DEE) was not affected by the clutch size manipulation. Female DEE was significantly higher than male DEE, and this could be caused by the fact that only the female roosts with the young. There was no consistent relationship between DEE and parental survival or future reproductive success. Since the experimental reduction in clutch size led to an increase in residual reproductive Value (more second clutches), but not to a decrease in DEE, this costs of reproduction is apparently not contingent on increased rate of energy turnover. It is suggested that birds with equal DEE may differ in their residual reproductive value as a consequence of variation in energy allocation between reproductive effort and e.g. aspects of physiological maintenance and repair. [KEYWORDS: Parus major; clutch size; parental effort; daily energy expenditure Doubly labeled water; flycatcher ficedula-albicollis; measuring energy-metabolism; starlings sturnus-vulgaris; kestrel falco-tinnunculus; brood size; breeding birds; reproductive effort;savannah sparrows; expenditure]

Throughout the animal kingdom, larger males are more likely to attain social dominance. Several lines of evidence suggest that this relationship extends to humans, as height is positively related to dominance, status and authority. We hypothesized that height is also a determinant of authority in professional refereeing. According to the International Football Association Board, FIFA, football (“soccer”) referees have full authority to enforce the laws of the game and should use their body language to show authority and to help control the match. We show that height is indeed positively related to authority status: referees were taller than their assistants (who merely have an advisory role) in both a national (French League) and an international (World Cup 2010) tournament. Furthermore, using data from the German League, we found that height was positively associated with authoritative behavior. Taller referees were better able to maintain control of the game by giving fewer fouls, thereby increasing the “flow of the game”. Referee height was also positively associated with perceived referee competence, as taller referees were assigned to matches in which the visiting team had a higher ranking. Thus, height appears to be positively related to authority in professional refereeing.

Eurasian Oystercatchers Haematopus ostralegus ostralegus are a classic example of individual feeding specialization. Feeding specialization causes morphological differentiation in Oystercatchers’ bill shapes due to varying degrees of abrasion associated with specific handling techniques for each prey species. Consequently, the Oystercatcher’s bill shape has been used as a proxy for diet specialization, as it provides a quick and easy way to assess the diet choice of this marine top-predator. However, bill shapes of Oystercatchers are categorized visually in distinct types, while it has been argued that the relevant variation is continuous. Also, it is unclear how comparable the bill-shape classification is among studies and between the sexes and how universal bill shape–diet relationships are. Here we investigate the usefulness of bill-shape types as a proxy for diet choice in Oystercatchers, using four new and two published datasets. We show that quantitative bill-morphometrics provide no evidence that bill-shape types are discrete entities. Additionally, the dimensions of the same bill-shape type differ across studies. This difference is unlikely to be caused by methodology and might reflect subtle additional feeding specialization among birds with the same bill-shape type. Moreover, we show that the tip of the bill of males is typically 7% higher than that of females with the same bill-shape type. A higher – and probably stronger – bill tip in males may explain why males had more shellfish in their diet than females with the same bill-shape type. Finally, a literature-review shows that the exact bill shape–diet relationship differs between studies and the sexes. We conclude that the interpretation of bill-shape type as a proxy for diet choice in Oystercatchers is context dependent. We propose that quantitative bill dimensions are a better proxy for feeding specialization than bill-shape types.

Density dependent processes and the availability of food may play an important role in the determination of population size. To investigate the relationship between density and local survival of juvenile Great Tits Parus m. major Kluyver removed first brood fledglings in two years. An analysis is presented of the effects of this removal experiment, beech crop and additional feeding in winter on local survival. Beech-crop index was positively correlated with local survival of both first- and second-brood fledglings. Additional feeding in winter affected local survival of first, but not of second-brood fledglings. The effect of the removal experiment differed between birds fledging early or late in the season. Removal of first-brood fledglings had a negative effect on local survival of the remaining first-brood fledglings. This effect was in accordance with the (quadratic) relationship between density and survival found in control years, indicating that the relationship is causal. This is a destabilizing density dependent process. Possible underlying mechanisms are discussed. Removal of first-brood fledglings enhanced local survival of second-brood fledglings. The enhancement was in accordance with the relationship found in control years, indicating that this relationship too is causal. Density of second-brood fledglings did not affect local survival of first or second-brood fledglings. This study confirms that food and density-dependent processes play an important role in the determination of population size but the effect of these factors differs between birds fledging early or late in the season.

Seasonal variation in reproductive success is a common feature of most organisms. To understand the evolution of breeding seasons and reproductive strategies of individual animals, it is necessary to assess the extent to which seasonal variation in reproductive success is causally related to seasonal variation in the environment ('timing' hypothesis), to differences in quality between early and late breeders or their territories ('quality' hypothesis), or to a combination of both. We manipulated timing of breeding in the Great Tit Parus major, a small passerine, to test these hypotheses. A group of experimentally delayed birds was created by removing first clutches, inducing birds to lay a replacement clutch. Reproductive success of delayed pairs was compared with control pairs that bred early and with pairs that bred late. We conclude that seasonal declines in reproductive success at the nestling stage and survival of adult females were caused by differences in quality between early and late breeders. Recruitment of fledglings into the breeding population and the occurrence of second clutches were causally related to the timing of breeding. The seasonal decline in clutch size was caused by a combination of timing and quality effects. We attempted to assess the relative importance of timing and quality in the seasonal decline in reproductive success, expressed as lifetime production of recruits. We tentatively conclude that 87% of the seasonal decline in lifetime reproductive success could be attributed to a timing effect per se, whereas quality differences between early and late breeders accounted for the remaining 13%. [KEYWORDS: Clutch size; environmental quality; laying date; parus major; phenotypic quality; reproductive success Parus-major; causal relationship; fledging success; laying date; clutch size; survival; winter; flycatcher; population;fitness]