Late Nests Research Articles

Temporal Patterns of Fitness and Survival in the Wood Thrush

Data from a 22-yr study of individually marked Wood Thrushes (Hylocichla mustelina) in a Delaware forest fragment were analyzed to determine temporal and demographic patterns of nesting success, recruitment of local young into the population (fitness), and adult return rates (survival). Clutch size, number of eggs incubated, and number of eggs hatched were greater in early nests than in late nests. Although no difference existed in the average number of fledglings produced from early and late nests, fledglings from early nests were more likely to be recruited as breeders in the local population. Pairs of yearling (SY) birds produced equal numbers of recruits per nest from early and late nests, whereas pairs of older (≥2-yr-old, ASY) birds produced more recruits from early nests. The probability of fledging at least one young tended to be greater for late nests, and the percentage of eggs that eventually fledged was also greater for late nests. All nests were most likely to fail in the laying stage than during any other nest stage. Early nests failed in the laying stage at a greater rate than late nests. The number of Wood Thrushes that hatched was the most important demographic, reproductive, or date variable measured that positively influenced seasonal fledging success. Year of breeding also positively influenced success. ASY birds returned to breed at higher rates than did SY birds. SY males returned at a higher rate than did SY females. There was no difference in return rates between ASY males and ASY females. Producing at least one Wood Thrush fledgling positively influenced the likelihood of return for SY females. Neither annual success nor any other demographic, reproductive, or date variable that we measured influenced the return probabilities of other age or sex classes of adult birds. Based on these temporal patterns of fitness and survival, we propose that life history strategies among Wood Thrushes vary as a function of late-season reproductive effort and winter-related factors that affect survival.

TEMPORAL PATTERNS OF FITNESS AND SURVIVAL IN THE WOOD THRUSH

Data from a 22-yr study of individually marked Wood Thrushes (Hylocichla mustelina) in a Delaware forest fragment were analyzed to determine temporal and demographic patterns of nesting success, recruitment of local young into the population (fitness), and adult return rates (survival). Clutch size, number of eggs incubated, and number of eggs hatched were greater in early nests than in late nests. Although no difference existed in the average number of fledglings produced from early and late nests, fledglings from early nests were more likely to be recruited as breeders in the local population. Pairs of yearling (SY) birds produced equal numbers of recruits per nest from early and late nests, whereas pairs of older (≥2-yr-old, ASY) birds produced more recruits from early nests. The probability of fledging at least one young tended to be greater for late nests, and the percentage of eggs that eventually fledged was also greater for late nests. All nests were most likely to fail in the laying stage than during any other nest stage. Early nests failed in the laying stage at a greater rate than late nests. The number of Wood Thrushes that hatched was the most important demographic, reproductive, or date variable measured that positively influenced seasonal fledging success. Year of breeding also positively influenced success. ASY birds returned to breed at higher rates than did SY birds. SY males returned at a higher rate than did SY females. There was no difference in return rates between ASY males and ASY females. Producing at least one Wood Thrush fledgling positively influenced the likelihood of return for SY females. Neither annual success nor any other demographic, reproductive, or date variable that we measured influenced the return probabilities of other age or sex classes of adult birds. Based on these temporal patterns of fitness and survival, we propose that life history strategies among Wood Thrushes vary as a function of late-season reproductive effort and winter-related factors that affect survival.

Sex ratio in relation to timing of breeding, and laying sequence in a dimorphic seabird

When the cost of rearing sons and daughters differs and the subsequent survival and reproductive success of one sex is more dependent than the other, on the amount of parental investment, adult females tend to produce more chicks of the more dependent sex if the females are in good condition themselves. One method of varying the total investment in each sex is through modifying the sex ratio of offspring produced. This study shows that in broods of European ShagsPhalacrocorax aristotelis, the sex ratio varied with laying date. Presumably in this species, the lifetime reproductive success of males is more dependent on the level of parental investment. Early breeders are in better condition, the brood sex ratio of early broods was male biased (0.63), while that of late broods was female biased (0.36). The overall difference in sex ratio found between early and late nests could be attributed to manipulation of sex in the first laid egg. In early broods, 77% of the first hatched chicks were male but only 30% of the first hatched chicks in late broods were male. The sex combination of the first two chicks in a brood significantly affected growth as measured by asymptotic mass.

Strategies of the Cooperatively Breeding Noisy Miner to Reduce Nest Predation

SummaryNest predators reduce the reproductive success of passerines and may also threaten the safety of adult breeders. This paper investigates potential strategies used by cooperatively breeding Noisy Miners Manorina melanocephala at a site in south-east Queensland to reduce the risk to their nests. First, nearly twice as many nests were built from June to September as from October to January. Conversely, the availability of insects needed to feed chicks was known to be higher in the warmer months. Predation risk was probably driving the timing of breeding, because early broods were significantly less likely to be preyed upon than were those built later in the year. Second, low nests (less than 2.5 m high) were more likely to be successful than nests built at heights of over 4 m. Low nests are less visible and accessible to raptors. No other measures of nest concealment or accessibility were linked with nest success. However, early nests were significantly better concealed than late nests. Noisy Miner nests are probably fairly obvious to diurnal predators because of the activity of many visitors around them, and the loud begging calls of nestlings. Finally, the number of visitors to a nest was not correlated with the fate of that nest. In conclusion, there was no single strategy for reducing the risk to noisy miner nests of predation. This was probably due to the diverse taxonomic range of potential nest predators at the study site.

Reproductive consequences of egg‐laying decisions in snow geese

Summary1. Even though feeding conditions typically improve over time during the laying period, clutch size decreases over the course of the nesting period in most bird species. We examined whether seasonal decrease in offspring value could explain the seasonal decline in clutch size in arctic‐nesting greater snow geese (Anser caerulescens atlanticusL.).2. Nesting was synchronized within a year, with more than 90% of the nests being initiated within about 8 days. Despite this high synchrony, there was a steep seasonal decline in clutch size in each of the 7 years of the study, from about five eggs in early clutches to three in late ones (−0·20 egg day−1).3. Late parents performed more poorly than early parents in most components of reproductive success. The relationship between laying date and nesting success was curvilinear, early and late nests having a higher failure rate than those initiated near the median. Prefledging survival decreased by about 50% over the season, although the earliest hatched goslings also tended to have a reduced survival. The postfledging survival showed the strongest seasonal decline, as survival probability of late‐hatched birds was about five times lower than in early‐hatched ones.4. Overall reproductive success showed a very steep seasonal decline as the number of young surviving to the first winter was about eight times lower in late‐nesting birds than in early‐nesting ones. Reproductive success declined slightly in the earliest‐nesting birds, suggesting a cost to nesting too early.5. The observed clutch size generally matched the clutch size that yielded the highest reproductive success for each laying date, except in earliest‐nesting birds which should have done better by slightly delaying nesting. Our data suggest that trading off additional eggs for earlier nesting to increase reproductive success is an option in geese. Consequently, the seasonal decline in clutch size may be an adaptive response to seasonally declining survival prospects of offspring.

Relationships of Habitat Patch Size to Predator Community and Survival of Duck Nests

We studied duck nest success and predator community composition in relation to size of discrete patches of nesting cover in the Prairie Pothole Region (PPR) of the United States in 1993-95 We focused on nests in uplands that were seeded to perennial grasses and forbs and enrolled in the Conservation Reserve Program (CRP) in Minnesota, North Dakota, and South Dakota. We estimated daily survival rates (DSRs) of upland duck nests and indices of activity for red foxes (Vulpes vulpes), coyotes (Canis latrans), American badgers (Taxidea taxus), striped skunks (Mephitis mephitis) and Franklin's ground squirrels (Spermophilus franklinii) and related these variables to habitat patch size. The effect of patch size (small vs. large) on estimated annual mean DSR was dependent on date of nest initiation (early vs. late) and year. Examination of within-year comparisons for early and late nests suggested that DSR was generally greater in larger habitat patches Activity indices for the 5 mammalian nest predators were influenced differently by year, location, and patch size. Activity indices of the red fox were greatest in small patches. Coyote indices were the most inconsistent, demonstrating a year × location × patch size interaction. Activity indices of the striped skunk and American badger varied only among years. Franklin's ground squirrel indices were affected by study area location, with higher indices in the southeast than the northwest. Red fox activity was weakly correlated with that of the striped skunk and coyote. Although a positive relationship between habitat patch size and nest success probably exists, we believe the experiment to fully test this hypothesis will continue to be elusive.

An alternative approach to the measurement of seasonal trends in bird breeding success: a case study of the bullfinch Pyrrhula pyrrhula

1. On the basis of juvenile:adult ratios among netted birds and studies of moult, inferences are drawn about seasonal and annual variation in the breeding output of a bullfinch population studied near Oxford, in southern England. 2. In most years during 1962–66, the juvenile:adult ratio among netted birds increased from July or August to October, and then declined. The ratio in October, taken as a measure of annual productivity, varied between 2·8 and 5·5 in different years. 3. In the Oxford area, egg‐laying among bullfinches occurred between mid‐April and late August, so that the last young of the year left the nest in late September/early October. However, not all pairs continued breeding this late in the year. Individual bullfinches started to moult when they finished breeding. The proportion of adults which started moult after 20 August (implying successful breeding from eggs laid after mid‐July) varied between 7 and 68% in different years (or between 19 and 63% using a different method of estimation). Juveniles from these late nests, identified as those starting moult after 31 August, formed 24–61% of the total juvenile population in different years, the rest having been produced from clutches begun before mid‐July. 4. In the 2 years when the greatest proportions of adults started to moult after 20 August and the greatest proportion of juveniles started after 31 August, the juvenile:adult ratios in October were highest. By implication, the two‐fold variations in overall productivity between years were associated primarily with variations in the amount of late breeding. 5. This study, based on moults and age‐ratios among netted birds, provided information on seasonal productivity that was practically impossible to obtain in this species by conventional nest finding. An implication was that an interaction between the seasonal pattern of breeding in particular years and a seasonal trend in predation on nest contents, had major effects on overall annual productivity.

Seasonal Decline of Growth and Fledging Success in Snow Geese Anser caerulescens: An Effect of Date or Parental Quality?

Late-nesting birds frequently have a lower reproductive success than early-nesting ones. This could be a consequence of seasonal variations in environmental conditions or because late-nesting parents are of lower quality than early-nesting ones. We tested the hypothesis that a difference between early and late parents in their ability to raise viable offspring could explain the seasonal decline in offspring growth and survival in the Greater Snow Goose Anser caerulescens atlanticus, a species with self-feeding precocial young. Over two years, we exchanged complete clutches between early and late parents, to change the hatching date experienced by parents. We exchanged eggs between 164 experimental nests, whose hatching dates differed by 0 to 9 days (R= 3 days). We detected no seasonal effect on survival rate in the sample of experimental nests, but there was a seasonal decline of growth rate. When delaying or advancing hatching, the fostered goslings grew respectively slower or faster compared to the parents' original hatching date, indicating that variations in environmental conditions are responsible for seasonal variation of growth. However, growth of experimental goslings did not differ from unmanipulated goslings hatched at the same date, indicating that parental quality did not contribute to seasonal variations of growth rate. We conclude that the seasonal variation in reproductive success is not caused by a difference in parental quality between early and late nesters, but mostly by environmental factors directly related to the date of the season.

Male and female behaviour and extra-pair paternity in the wheatear

Behavioural observations and DNA fingerprinting were used to determine the relationship between male and female behaviours and levels of extra-pair paternity in the wheatear,Oenanthe oenanthe. Behavioural observations were consistent with the hypothesis that males attempted to ensure paternity by mate guarding, while pursuing extra-pair copulations (EPCs) primarily outside the fertile period of their pair female. The intensity of guarding varied with time of season and was greater at late nests. However, although males on territories with late nests also experienced high intrusion rates, the intensity of guarding was influenced more by the operational sex ratio (which was female skewed at early nests) than by intrusion rates per se. We suggest that early breeding males adopted a strategy of territorial defence to ensure paternity, as opposed to guarding their female directly (which late breeding males did), to capitalize on the increased opportunities to pursue EPCs in neighbouring territories. Females were less conspicuous than males in their pursuit of EPCs, were never seen off territory or observed to solicit extra-pair males directly, and rejected the majority of EPCs. The frequency of extra-pair paternity was 11% of 73 offspring, in 29% of 17 broods, and was not correlated with the intensity of guarding. Female cooperation appeared to be important for successful copulation, and extra-pair paternity is therefore likely to be a consequence of solicited, or at least accepted, EPCs. We discuss why females might have participated in EPCs.

Seasonal variation in breeding performance and nestling diet of Cirl Buntings Emberiza cirlus in England

The survival rates and outcomes of Cirl Bunting nests were recorded over a four-year period. Significant annual variations in nest survival were found at both the egg and the young stage. Significant seasonal variations in survival rates were found, with late nests being over twice as likely to produce fledglings as early ones. Most losses occurred at the chick stage early in the season and were due to predation and starvation. Chicks in poor condition through food shortage may have been more likely to be predated as a result of increased begging activity. Late season chicks had a very different diet to those hatched early in the season, being fed a much higher proportion of Orthoptera. They also enjoyed higher growth rates and survival. Rainfall had a small detrimental effect on growth rates, probably as a result of insect prey becoming hard to find. Loss of arthropods due to intensification of livestock farming and loss of diversity in the agricultural landscape may have contributed to the decline of the species in the UK.

Shiny cowbirds follow the ‘shotgun’ strategy of brood parasitism

Brood parasitic cowbirds,Molothrusspp., should lay their eggs in host nests at a time that maximizes both the probability of acceptance by the host and the chances of survival for the parasitic egg and young. Moreover, because multiple parasitism of a host nest is likely to result in low cowbird success, cowbirds are expected to avoid it by defending nests or laying territories, avoiding already parasitized nests or by destroying previously laid cowbird eggs. Shiny cowbird,M.bonariensisegg-laying behaviour was studied in house wren,Troglodytes aedonnests, to determine whether cowbirds monitor host nests to lay their eggs in synchronization with the host's laying period, and whether cowbirds avoid multiple parasitism. Shiny cowbirds monitored nests of house wrens during early and late nest building and during egg-laying stages. Each female cowbird monitored several wren nests over several days, and each wren nest was monitored by several cowbirds. Although to some extent shiny cowbirds synchronized egg laying with their host, they did it in a fairly sloppy manner. Of 185 cowbird eggs laid in 40 nests, 47% were laid in coincidence with the wrens’ laying period, but 35% were laid before the wrens started laying, and 18% were laid after wrens had finished laying and started incubation. Cowbirds also laid 82 eggs in 20 nests that were abandoned by wrens before laying. Multiple parasitism was common and cowbirds did not avoid multiply parasitized nests. There was no evidence that cowbirds removed previously laid eggs, and only six of 150 cowbird eggs were destroyed in nests. Therefore, shiny cowbirds seem to follow a ‘shotgun’ strategy; i.e. they rely more on high fecundity and chance than on the precise placement of each egg. This strategy is possible with house wrens because wrens do not reject cowbird eggs.

Productivity of Nesting Spectacled Eiders on the Lower Kashunuk River, Alaska

We studied the chronology and success of nesting Spectacled Eiders (Somateria fischeri) along the lower Kashunuk River on the Yukon-Kuskokwim Delta from 1991-1995. Nest initiation dates ranged from 16 May-22 June. Median nest initiation dates were correlated with the break-up of ice on the Kashunuk River. Clutch sizes declined seasonally, and mean clutch size varied among years ranging from 4.8-5.6 eggs. The frequency of nests containing inviable eggs (24% of successful nests, x = 0.6 unhatched eggs per successful nest) did not differ among years or nest initiation dates, and may be related to exposure to contaminants. The rate of partial depredation also did not vary among years or initiation dates (23% of nests, x = 0.5 eggs taken/successful nest). We detected no effect of marking or visitation on daily survival rate of nests. Nests initiated early in the year were more successful than late nests; thus, early nesting females laid larger clutches and were more likely to nest successfully than late nesters. Nest success varied among years and declined from 73% in 1991 to 18% in 1994. Nest success increased to 76% in 1995 when we reduced the Mew Gull (Larus canus) population on the study area. While inviability and partial depredation averaged over 1 egg per successful nest, the production lost in nests that were abandoned or completely destroyed by predators was much greater. Our data indicate that Spectacled Eiders nesting on our study area experience relatively high production; however, without information regarding annual survival and recruitment. it is not possible to draw conclusions about population growth rates.

Parental attendance and squatting in the KittiwakeRissa tridactyladuring the rearing period

Parental attendance was studied in 1991 in the Cap Sizun Kittiwake colonies (Brittany, France). After a period of continuous guarding lasting on average 22 days, parents left their chicks unattended. Thereafter, parental attendance decreased regularly until fledging. The chick age when first left alone was on average 3 days lower for large broods than for single-chick broods. Moreover, whatever the brood size, chicks from late nests were younger when left unattended. Parental age affected the initiation of first absence. Younger parents reduced their attendance sooner than older parents. About 80% of the nests with chicks were visited by other adults at least once during the absence of the parents, and 50% were visited in the 3 days following the first absence of the breeders. These squatters were mainly failed breeders and prebreeders looking for a future breeding site. The results are discussed in terms of costs and benefits of chick neglect and comparisons were made with data from other studies in Nort...

Long-Term Declines in Nest Success of Prairie Ducks

Increased predation on nests of ducks in prairie uplands, as a result of habitat alteration, has been hypothesized to cause decreased nest success and population sizes. We tested whether, and by how much, nest success declined using data compiled from 37 studies conducted between 1935 and 1992 at 67 sites in the Prairie Pothole Region of Canada and the United States. Nest success declined (P = 0.0002) over time, but time explained only 10% of the variation ; precipitation (P = 0.79) did not account for additional variation in nest success. Nest success declined at similar (P = 0.13) rates among 5 species, but late nesters (gadwall [Anas strepera], blue-winged teal [A. discors], and northern shoveler [A. clypeata]) had higher success (P = 0.004) than early nesters (mallard [A. platyrhynchos], and northern pintail [A. acuta]). Populations of gadwalls and northern shovelers, however, have not declined, indicating that declines in nest success may not be related causally to population change. Long-term population declines in blue-winged teal, northern pintails, and mallards coincide with large-scale temporal declines in nest success. Declines in nest success were parallel in parkland and grassland regions, suggesting a causal agent (or agents) that act(s) at a broad scale, despite inherent differences in the composition of the predator communities and habitats between regions.

Seasonal Decline in Clutch Size of the Barnacle Goose in Svalbard

We examined seasonal decline in clutch size in the high arctic Barnacle Goose Branta leucopsis in Svalbard. Females that arrived first at the breeding ground nested first, had the longest prelaying period, produced the largest clutches and also had the longest incubation period. Nevertheless, their brood size at hatching was larger than late nesters. These results do not support the nutrient reallocation hypothesis which suggests that seasonal decline in clutch size in arctic nesting geese results from the mobilization of nutrient reserves during the period before egg laying. Instead, we propose that geese which arrive late at the breeding area spend relatively less of their reserves on eggs. They do this presumably to achieve synchronous hatching with early nesting birds and/or to prevent a late breeding season which may reduce gosling survival, adult survival and/or future fecundity.

An evolutionary explanation for seasonal trends in avian sex ratios

We present an extensive set of data for five species of raptorial birds to demonstrate that some raptor species produce an excess of daughters early in the season and an excess of sons in late nests, while others show the reverse. By means of a simulation model we investigate an evolutionary explanation for this phenomenon in terms of sex-specific differences in the relation between age at first breeding and date of birth. The model predicts that that gender should be produced first in the season whose age of first breeding is more strongly accelerated by an early birth date. We argue that this tends to be the male gender in raptor species, such as the common kestrel (Falco tinnunculus), which tend to breed early in life, while it is the female gender in larger species with later onset of breeding, such as the marsh harrier ( Circus aeruginosus). The empirical evidence is qualitatively consistent with this hypothesis. Our model is quite general in that it makes no assumptions about the mechanism (primary sex-ratio bias at egg laying or secondary sex-differential mortality before fledging) by which the bias is generated. Yet it is able to create quantitative predictions for species where sufficient demographic and life-history data are available. From the available data set in the common kestrel we derive a quantitative prediction for the seasonal trend in brood sex ratio. The observed trend is in good agreement with this prediction.

Nest-building by crested tit Parus cristatus males: an analysis of costs and benefits

In a population of crested tits in Belgium, one out of three breeding males participated in nest-building. Since variation in the amount of nest-building among 11 building males was low, analysis of male nest-building allowed a logistic regression design. The probability of building increased with male condition and for late nests. The effect of male condition decreased with date, and date was the only factor predicting nest-building for repeat broods. The effect of male condition on nest-building suggests that building entails important costs for males. Based on correlative data, we argue that building by males shortens the interval between the start of nest-building and the onset of egg-laying by about 5 days. Since clutch size, incubation and nestling time did not differ between early and late broods, male nest-building apparently affects fledging date. Since early fledgers (early dispersers) are more likely to settle in future winter flocks, building behaviour by crested tit males should be favoured by natural selection. So far, male nest-building in hole-breeding birds might have been overlooked due to the widespread use of artificial nest-boxes in behavioural studies.

Nutrition of Breeding Female Ruddy Ducks: The Role of Nutrient Reserves

We determined fat, protein, and mineral content of somatic tissue, and estimated amounts of these nutrients committed to eggs by Ruddy Ducks (Oxyurajamaicensis) nesting in southern Manitoba in 1988. Seasonal nutrient dynamics differed between breeding and nonbreeding females. Nonbreeders had less fat and protein reserves than did breeders early in the nesting season, but these then increased and subsequently declined, whereas nutrient reserves of breeders declined linearly with date from the outset of our study. Onset of breeding was related to a nutrient reserve threshold (early RFG [rapid follicle growth] ducks had 22.7 g more fat and 5.1 g more protein than did non-RFG ducks). Adults showed greater propensity to initiate breeding (73% of breeding population) than did yearlings (68% of nonbreeding population), and we relate this to greater fat and protein reserves of adults. Adult breeders had more fat and protein reserves than did yearlings at every stage in the breeding cycle but no age-related differences in use of fat, protein or mineral reserves for clutch formation were found. When controlling for date effects, fat reserves declined (b = -0.49) as fat was committed to eggs. Early nesters initiated and ended egg laying with significantly more fat compared to late nesters, although rate of fat use was not different. Protein and mineral reserves were used for clutch formation by early nesters (b = -0.24 and -0.08, respectively), but not by late nesters. Among females nearing end of laying, number of developing follicles was related to mineral, but not fat or protein reserves, indicating that mineral reserves were a proximate factor constraining clutch size. Our findings confirm that, for Ruddy Ducks, somatic tissues are important sources of nutrients for clutch formation, and that clutch size is directly related to mineral reserves. Of importance to lifetime reproduction, and thus fitness, is our finding that minimum levels ofnutrient reserves appear critical for initiation of breeding by female Ruddy Ducks.

Intraspecific brood‐parasitism and dispersal in fledgling Sparrowhawks Accipiter nisus

The progeny of early‐nesting Sparrowhawks Accipiter nisus have a higher survival rate than those of late nesters. To ascertain the reasons for greater survival in early‐season Sparrowhawk fledglings, I studied post‐fledging dispersal behaviour in this species by direct observations and radio‐tracking during 3 years in Rockingham Forest, Northamptonshire, U.K.Post‐fledging brood‐parasitism was found among early‐dispersed young of both sexes.Early‐dispersed young spent up to 6 days being fed by the parents of other fledged, but still dependent, broods, as far as 6 km from their own nests.Three broods were provided with supplementary food for 4 weeks, starting 1 week before expected dispersal. These young dispersed when significantly older than young from control broods. In both groups, males dispersed, on average, 3–4 days earlier than females. The ultimate dispersal age of young in control broods was negatively correlated with their rate of mass gain during the nestling period. Unlike the young of the control broods, fledglings in broods with augmented food were usually silent.These findings offer an explanation for why Sparrowhawk young that disperse early in the season survive better than those which disperse late.

Effects of male removal on the behaviour and reproductive success of female Eastern Bluebirds Sialia sialis

We removed male Eastern Bluebirds Sialia sialis to examine the importance of male parental care and the behavioural responses of unaided females to loss of male assistance. Unaided females fed young significantly more than control females (females with male assistance) fed young, but young in experimental nests were fed significantly less frequently in total than young in control nests. Unaided females had significantly lower nesting success (fledged at least one young) than control females. At control nests, males defended the young more strongly than did their mates. Unaided females defended their young as strongly as control females. Unaided and control females spent the same amount of time brooding young, and there was no tradeoff between feeding and brooding young. Most early season experimental nests failed, but late in the season many unaided females were as successful as pairs. Unaided females were able to match the feeding rat'e in control broods at late nests but not at early nests, where control nestlings were fed at a higher rate. In our population, male bluebirds played an important role in provisioning young, and early in the season unaided females were unable to provide sufficient bod to raise any young to fledging.