Cornelis Dijkstra

Sex identification in birds using two CHD genes

In theory, birds should control the sex ratio of the offspring they produce. In practice, we have very limited evidence to support this idea because of our difficulty in sexing nestling birds. In addition, extinction is facing an increasing number of birds. Our ability to help includes captive breeding which, again, is difficult if male and female adults cannot be recognized. Here we describe the discovery of a W-linked gene in the Great tit (Parus major). It is named CHD-W (chromodomain-helicase-DNA-binding protein W-linked), it is highly conserved and it is W-chromosome linked in a range of bird species. These birds also possess a second, non-W-linked CHD gene (CHD-NW). A single, simple polymerase chain reaction technique based on both genes can be used to identify the sex in a wide variety of birds.

Brood size manipulations in the kestrel (Falco Tinnunculus) : Effects on offspring and parent survival

(1) Brood reductions and enlargements were carried out in kestrel nests to evaluate the consequences of raising different numbers of nestlings for both the offspring and the parents. (2) Brood enlargements caused increased daily hunting activity of the parents, reduced growth rate of the nestlings, increased nestling mortality and enhanced weight loss in the female parent. Brood reductions caused an increased food intake by the nestlings, in spite of (non-significantly) reduced parental hunting activity. Local survival of the parents was negatively correlated with the experimental change in brood size. (3) A review of the literature on brood enlargements is presented, showing that parents were able to raise more young till fledging than their natural broods in twenty-nine out of forty altricial bird species investigated. Negative effects of brood enlargements on parental survival or future reproduction were established in eight out of twelve species investigated. (4) The results are consistent with the theory that parental work for the offspring entails an inherent reduction in future reproductive output and that natural broods, by being smaller than the maximum number of nestlings that can be raised, maximize the total reproductive output.

Adaptive seasonal variation in the sex ratio of kestrel broods

In contrast with the situation in mammals, sex ratio variations of offspring in birds have rarely been documented, and never been shown to be adaptively tuned to systematic differences in the prospects for daughters and sons. The sex ratio (% males) in broods of European kestrels, Falco tinnunculus L., declined with progressive date of birth. This decline enhanced reproductive prospects of the broods since the probability of breeding as yearling declined with birth date for male offspring, but not for females. The sex ratio bias of the brood was produced by non-random sex segregation at meiosis: by altering the within-clutch sequence of sexes (first male then female eggs in early clutches, the reverse in late clutches) laying kestrels assigned the sex with the better long-term reproductive prospects to the initial eggs of their clutch, which suffer least mortality in the nest. file: 1990FunctEcolDijkstraC.pdf Gebruik a.u.b. deze link om te verwijzen naar dit document: http://irs.ub.rug.nl/dbi/4e16b2d622f03

Hunting in the Kestrel, Falco tinnunculus, and the Adaptive Significance of Daily Habits

Summary1.In an attempt to evaluate the importance of individual daily habits to a freeliving animal, foraging behaviour of kestrels was observed continuously for days in sequence in open country. Data obtained in 2,942 observation hours were used. Flight-hunting was the prominent foraging technique yielding 76% of all prey obtained.2.Flight-hunting was impeded by rain, fog and wind speeds below 4 m/s and above 12 m/s (Fig. 3). Flight-hunting tended to be suppressed also in response to recent successful strikes and more generally by a high level of post-dawn accumulated prey (Figs. 4, 5). Flight-hunting had a tendency to be enhanced in response to recent unsuccessful strikes (Fig. 6).3.Trapping results demonstrated a fine-grained daily pattern of common vole trap entries, with peaks at intervals of ca. 2 h (Figs. 7, 8). The interpretation of some of this pattern as representative of vole surface activity was supported by overall strike frequencies of kestrels hunting for voles (Fig. 9).4.Detailed analysis of the behaviour of three individuals revealed significant peaks in hunting yield and frequency, coinciding with each other and with peaks in vole trapping (Fig. 11). It is suggested that the kestrels adjusted their flight-hunting sessions to times of high ‘expected’ yield. Vole activity peaks sometimes remained unexploited.5.Meal frequencies culminated shortly before nightfall except in incubating females. The difference between the daily distributions of hunting and eating was due to some of the prey being cached in daytime and retrieved around dusk (Fig. 13). Caching behaviour is interpreted as a circadian strategy allowing separate optimization of hunting-adjusted to prey availability-and eating-adaptive by retaining minimum body weight in daytime flight and by thermo-regulatory savings at night.6.Some kestrels showed remarkable constancy from day to day in the temporal distribution of specific behaviours (Fig. 16) and of spatial movements (Figs. 18, 19). In three 1–2 week sequences of observation analysed, flight-hunting frequency peaked 24 h after prey capture (Fig. 17). This is probably based on day to day correlations in flight-hunting frequency as well as on increased motivation for hunting in response to prey capture 24 h ago (Table 5).7.In one individual with three distinct hunting areas, the tendency to return to an area again was maximal 24 h after prey capture in that area (Fig. 21, Table 6). A field experiment tested the effect of prey capture on the daily distributions of hunting and site choice in this individual (Fig. 22). A significant concentration of flight-hunting activity in the experimental feeding area was observed at the daily time of feeding (Fig. 23). Two alternative hypotheses are compatible with the result. Favoured is the one that the birds use “time memory” for the optimization of their daily patterns of flight-hunting and site choice.8.By adjusting her daily flight-hunting to times of high yield, one kestrel saved 10–22% on her total time spent flight-hunting. Maximal efficiency, by concentration of all hunting activity in the hour of maximal yield, was not attained, presumably because of information constraints. The generality of the contribution of daily habits to survival is discussed.

Energetic limitation of avian parental effort : Field experiments in the kestrel (Falco tinnunculus)

We studied the limiting factors for brood size in the kestrel, Falco tinnunculus, by measuring parental effort in natural broods of different size and parental response to manipulation of food satiation of the brood. Parental effort was quantified as total daily time spent in flight, and total daily energy expenditure, from all‐day observations.

Time allocation in the kestrel (Falco tinnunculus), and the principle of energy minimization

(1) Time allocation of the kestrel in the Netherlands was established by dawn to dusk observation of focal birds. Time budgets were analysed with respect to time of year, phase of the breeding cycle, sex and weather conditions. (2) The common vole, Microtus arvalis L., was the major food source (92% of food items caught) with minor additions, especially in summer, of common shrews, Sorex araneus L., songbirds and juvenile waders. (3) Flight-hunting and perching were the two main foraging modes. Flight-hunting yielded, on average, 2.2 small mammals h-1 in winter and 4.7 in summer. Perching yield dropped from 0.3 mammals h-1 in winter to below 0.1 in summer. Flight-hunting yield reflected seasonal variations in food availability, perching yield did not. (4) There was no stage in the annual cycle where available daylight limited the daily flight-hunting time. There were no weather conditions where daily flight-hunting exceeded an average of 3.6 h or 20% of the active day. Stringent periods, in the sense that all buffer time is used for foraging, were found neither in winter, when food was scarce, nor in summer when food demand was highest. (5) Experimentally increased hunger of the brood led to increased male parental effort in terms of time spent flight-hunting plus flying, with a recorded maximum of 60% of the active day. Flight-hunting yield did not increase. (6) In winter, kestrels minimized energy expenditure, not foraging time, by using the low-cost low-profit technique of perch-hunting. In summer they maximized daily energy gain within limits probably set by their rate of food assimilation.

Seasonality of clutch size determination in the Kestrel Falco tinnunculus: An experimental approach

Egg numbers in Kestrel clutches decline from 6.5 to 3.2 with progressive laying date. Laying Kestrels did not respond to eggs added to the nest after the second egg. Egg removals starting on day 3, 5 or 7 of laying demonstrated that responsiveness (production of extra eggs) ceased ca 4 d before the normally final egg. Thus clutch fixation occurred sooner after the first egg in late than in early nests. Continuous records of nest temperature were used to establish incubation frequency of the female throughout laying in experimental and control nests. Incubation rose from 0 to 98% of time in the course of the laying phase. This rise started sooner and was more rapid in late nests and in nests with added eggs, and delayed in response to egg removal. The higher level of incubation tendency in late breeders at the onset of laying may be instrumental in more rapid follicle resorption and hence in clutch size reduction.

DAILY ENERGY EXPENDITURE OF MALE AND FEMALE MARSH HARRIER NESTLINGS

We used the doubly labeled water (DLW) method to measure daily energy expenditure (DEE) in eight brother-sister pairs of free-living Marsh Harrier (Circus aerugi- nosus) nestlings. We calculated metabolizable energy intake (ME) from DEE and body-mass change. In each pair, males had lower body mass, DEE, and ME than their female siblings. On average, male body mass was 20%, DEE 19%, and ME 20% lower than that of female siblings. Thus, energy turnover was proportional to body mass. Because the average sex ratio at fledging in Marsh Harriers is 55% male, and the energy requirement of sons is 45% of the son-daughter pair, this sex ratio matches exactly that predicted by Fishers theory (1930). A literature review revealed that DEE (kJ/ day) measured by DLW when nestlings were ap- proximately 95% of asymptotic or fledging mass scaled as 4.58 M 0-76 (where M = body mass in g) in 11 species of altricial nestlings, including the Marsh Harrier. Received 14 November 1996, accepted 3 December 1997.

Bill Redness Is Positively Associated with Reproduction and Survival in Male and Female Zebra Finches

Sexual traits can serve as honest indicators of phenotypic quality when they are costly. Brightly coloured yellow to red traits, which are pigmented by carotenoids, are relatively common in birds, and feature in sexual selection. Carotenoids have been linked to immune and antioxidant function, and the trade-off between ornamentation and these physiological functions provides a potential mechanism rendering carotenoid based signals costly. Mutual ornamentation is also common in birds and can be maintained by mutual mate choice for this ornament or by a correlated response in one sex to selection on the other sex. When selection pressures differ between the sexes this can cause intralocus sexual conflict. Sexually antagonistic selection pressures have been demonstrated for few sexual traits, and for carotenoid-dependent traits there is a single example: bill redness was found to be positively associated with survival and reproductive output in male zebra finches, but negatively so in females. We retested these associations in our captive zebra finch population without two possible limitations of this earlier study. Contrary to the earlier findings, we found no evidence for sexually antagonistic selection. In both sexes, individuals with redder bills showed higher survival. This association disappeared among the females with the reddest bills. Furthermore, females with redder bills achieved higher reproductive output. We conclude that bill redness of male and female zebra finches honestly signals phenotypic quality, and discuss the possible causes of the differences between our results and earlier findings.

Satellite tracking of two Montagu's Harriers (Circus pygargus): Dual pathways during autumn migration

Autumn migration routes of two Dutch female Montagu’s Harriers (Circus pygargus) were documented for the first time using satellite telemetry. Both migrated to their African wintering area—one via the Straits of Gibraltar through the Mediterranean and the other via Italy/Tunisia. The rate of travel was comparable to values reported for larger raptor species.