Clutch size and initiation date of ospreys: natural patterns and the effect of a natural delay

1993 ◽  
Vol 71 (11) ◽  
pp. 2141-2146 ◽  
Author(s):  
Christoph Steeger ◽  
Ronald C. Ydenberg
Keyword(s):  
Clutch Size ◽  
Food Availability ◽  
Reproductive Value ◽  
Canada Geese ◽  
Breeding Performance ◽  
Nestling Period ◽  
Optimal Clutch Size ◽  
Primary Nest ◽  
Clutch Initiation

We studied the breeding performance of ospreys (Pandion haliaetus) in southeastern British Columbia from 1987 to 1990. Clutch size, brood size, and the number of young fledged per nest all declined significantly as clutch initiation date was delayed. The quality of later born young as measured by growth rate and the number of fault bars in rectrices did not seem to be reduced. Behavioural observations of the flight-hunting performance of six focal males demonstrated that food availability did not decline in the course of the nestling period. Clutch initiation of some osprey pairs was naturally delayed when their nests were occupied by Canada geese (Branta canadensis). Nest occupation delayed clutch initiation by 9.4 days on average, and reduced clutch size by 0.2 eggs. Osprey pairs possessing an alternate nest were not delayed by the presence of geese in their primary nest, and did not reduce clutch size, suggesting that the clutch size reduction was a direct response to the delay, rather than to the presence, of geese. The results do not support the reduced food availability or reduced breeding commitment hypotheses for seasonal clutch size decline. The data conform to the predictions of the hypothesis that the optimal clutch size is set by a trade-off between the declining reproductive value of later hatched nestlings and the delay required to be able to enlarge the clutch.

Silver gull breeding at two colonies in the Sydney-Wollongong regio, Australia

1992 ◽  
Vol 19 (4) ◽  
pp. 429 ◽  
Author(s):  
GC Smith ◽  
N Carlile
Keyword(s):  
Clutch Size ◽  
Breeding Season ◽  
Food Availability ◽  
Breeding Success ◽  
Artificial Structures ◽  
Sydney Harbour ◽  
The 1960S ◽  
Almost All

Silver gulls have increased in abundance in Sydney-Wollongong this century. Both the number of colonies and their sizes have grown. The largest colony of 43 000-50000 pairs is on Big I., off Wollongong. Breeding was compared at this colony with that at a satellite colony on artificial structures in Rozelle Bay, Sydney Harbour. Breeding occurred from July to February at Big I., a lengthening of the season since the 1960s. At Rozelle Bay, breeding occurred almost all year round. Egg and clutch size varied within and between years at Big I. First-eggs of clutches, laid during the first breeding peak, were significantly larger than those laid later in each breeding season. The size of third-eggs in clutches differed between years. It is proposed that these disparities were a result of differences in food availability between years. Clutch sizes were significantly larger during the first breeding peak than later clutches of each season. Clutch size was larger at Rozelle Bay. Variation in clutch size was linked to quality of individuals and food availability. Breeding success at colonies was low, indicating that carrying capacities have been reached.

Family Planning in the Kestrel (Falco Tinnunculus): the Ultimate Control of Covariation of Laying Date and Clutch Size

Behaviour ◽  
1990 ◽  
Vol 114 (1-4) ◽  
pp. 83-116 ◽  
Author(s):  
Cor Dijkstra ◽  
Serge Daan ◽  
Joost M. Tinbergen
Keyword(s):  
Clutch Size ◽  
Brood Size ◽  
Experimental Approach ◽  
Causal Effect ◽  
Reproductive Value ◽  
Laying Date ◽  
Local Survival ◽  
Optimal Clutch Size ◽  
In Captivity ◽  
Ultimate Control

AbstractThe theory that individual birds maximize their fitness by the two major decisions in reproduction concerning date (when to start laying eggs) and clutch size (when to stop laying eggs) is empirically approached in the Kestrel by quantifying Fisher's Reproductive Value for both the clutch (Vc = c. Vo/2) and the parents (Vp). The reproductive value of an egg (Vo) was found to decrease monotonically with laying date (d) due to significant associations with d of the components So (probability for an egg to survive till fledging), S1 (probability to survive from fledging till age 1), S2 (survival age 1 till age 2), and P1 (probability of breeding at age 1). Vp declined negligibly with laying date, although there were significant associations between d (laying date) and N (probability of the nest to produce at least one fledging), Pr (probability of a repeat clutch following nest failure), and La (probability of local survival of the parents following breeding). In experiments where brood size at day 10 after hatching was increased or reduced, Vc increasing experimental brood size, while Vp simultaneously decreased. Total reproductive value (V = Vc + Vp) remained unaffected by the experiments. This result suggests that a rather broad range of clutch sizes maximizes total reproductive value, as far as detectable by the data. While the yield of kestrel hunting, and hence the number of young raisable with constant parental effort (and constant Vp), increased with the spring increase in vole population density, reproductive value of the clutches decreased. For any particular food situation (hunting yield) this leads to a unique combination of clutch size and laying date maximizing V. This could be worked out by calculating fitness contours for all combinations and for different yields (Fig. 12). The optimal solutions are on a declining slope, with smaller clutches associated with later dates. 59.4% of all clutches observed obeyed the maximization criteria. Furthermore, there was a reasonable, unbiased association between predicted laying dates and clutch sizes based on individual male hunting yields and observed dates and clutches as laid by the females. Qualitatively, any method predicts a seasonal decrease in the optimal clutch size when the environment improves while reproductive value declines with progressive date. Preliminary results from an experimental approach to test the assumption of a causal effect of date on Vo, using the release of juvenile kestrels reared in captivity under artificial light schedules, are presented.

Is there an Optimal Clutch Size in Snow Geese?

1987 ◽  
Vol 130 (6) ◽  
pp. 839-863 ◽  
Author(s):  
R. F. Rockwell ◽  
C. S. Findlay ◽  
F. Cooke
Keyword(s):  
Clutch Size ◽  
Snow Geese ◽  
Optimal Clutch Size

New Nesting Records and Breeding Ecology Observations of Rufous-legged Owls in the Mediterranean Temperate Forest of Central Chile

2021 ◽  
Author(s):  
Martín A. H. Escobar ◽  
M. Angélica Vukasovic ◽  
Jorge A. Tomasevic ◽  
Sandra V. Uribe ◽  
Ana M. Venegas ◽  
...  
Keyword(s):  
Clutch Size ◽  
Temperate Forest ◽  
Breeding Ecology ◽  
Ecological Data ◽  
Central Chile ◽  
Monterey Pine ◽  
Nestling Diet ◽  
Nestling Period ◽  
Nothofagus Forests ◽  
Southern Beech

ABSTRACT The Rufous-legged Owl (Strix rufipes) is the southernmost Strix owl species and its breeding ecology remains little known. We report new observations on the species' breeding ecology, including clutch size, egg size, duration of the incubation and nestling periods, and nestling diet. We conducted our observations on nests found during the summers of 1999 through 2004 in a forestry landscape of central Chile, dominated by Monterey pine (Pinus radiata) plantations with intermixed fragments of native southern beech (Nothofagus) forests. Clutch size was two eggs (n = 2 nests), with one egg larger than the other (mean = 48.8 × 40.1 mm). The incubation period was 30 d and the nestling period 34 d. We analyzed 10 pellets from nestling owls and identified 45 prey items, mostly dominated by large beetles, grasshoppers, and rodents (native and exotic). This information, though based on a limited number of nests, provides baseline ecological data that can inform future studies.

scholarly journals Behavior, Diet, and Breeding Biology of Double-Toothed Kites at a Guatemalan Lowland Site

The Condor ◽  
2000 ◽  
Vol 102 (1) ◽  
pp. 113-126 ◽  
Author(s):  
Mark D. Schulze ◽  
Jose LuÍs CÓrdova ◽  
Nathaniel E. Seavy ◽  
David F. Whitacre
Keyword(s):  
Clutch Size ◽  
Rainy Season ◽  
National Park ◽  
Maximum Density ◽  
Lowland Forest ◽  
Tropical Lowland ◽  
Nestling Diet ◽  
Tropical Lowland Forest ◽  
Nestling Period ◽  
Closed Canopy

Abstract We studied Double-toothed Kites (Harpagus bidentatus) in tropical lowland forest at Tikal National Park, Petén, Guatemala, documenting behavior and diet during the incubation and nestling periods. These 200-g kites are Accipiter-like in form and strikingly size-dimorphic for a kite. Modal clutch size was two, producing 0.63 fledglings per nesting attempt and 1.25 per successful nest. Nesting was largely synchronous among pairs, with hatching during the first month of the rainy season and fledging one month later. Incubation lasted 42–45 days and nestlings fledged at 29.5 days on average. A radio-tagged fledgling was fed near the nest for 35 days; 6–8 weeks after fledging it dispersed at least 10 km, presumably reaching independence. Males did not incubate or brood, and rarely fed nestlings directly. Males typically provided most but not all prey (mainly lizards) during incubation and early nestling periods. Insects in the nestling diet increased through the nestling period as females increasingly hunted, often bringing in insects. These kites hunted from perches, below and within the closed canopy of tall, mature forest, taking 60.5% insects, 38.1% lizards, and 1.4% other vertebrates; vertebrates comprised at least 75% of prey biomass. Most prey were taken from vegetation, but prey in flight also were captured. Active, adjacent nests averaged 1.35 km apart, for a maximum density estimate of 0.60 pairs km−2 and a more likely estimate of 0.33–0.50 pairs km−2 in homogeneous, favorable habitat and 0.29–0.44 pairs km−2 for Tikal National Park as a whole.

Competition, the Fitness of Offspring, and Optimal Clutch Size

1975 ◽  
Vol 109 (970) ◽  
pp. 677-699 ◽  
Author(s):  
Warren Y. Brockelman
Keyword(s):  
Clutch Size ◽  
Optimal Clutch Size
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