Feeding frequency influences crèching age in the Dalmatian pelican, Pelecanus crispus

Crèching behaviour is common in colonial seabirds; nevertheless, the factors inducing chicks to aggregate remain relatively poorly understood. It has been proposed that brood size, laying date and nest attendance are important factors in the formation of a crèche. Moreover, in most species of pelicans, chicks join crèches following the development of homoeothermy and coincident with the end of the brooding behaviour. We studied effects of feeding rate, nest attendance, brood size, laying date and homoeothermy on the age at which chicks entered the crèche at a colony of Dalmatian pelicans (Pelecanus crispus), in Srebarna, Bulgaria. Single chicks were fed more frequently than chicks from two-chick broods. Unlike American white pelicans (Pelecanus erythrorhynchos), Dalmatian pelicans maintained brooding behaviour a further 9 days after chicks had developed thermoregulation abilities. In contrast to nests with two chicks, nests with only one chick were never left unattended by the parents before the chick reached the crèching stage. Laying date, nest attendance and brood size did not affect the age that the chick entered the crèche. The age the chick entered the crèche was not correlated with the age of homoeothermy acquisition, but chicks significantly joined the crèche at younger ages when the mean number of feeds per chick per day during the rearing period in the nest was higher. This result suggests an implication of growth rate in the crèching age. Joining the crèche earlier can provide benefits that could have strong implications for the chicks’ future reproductive lives.     

Nestling feeding strategy of the British storm-petrel Hydrobates pelagicus in a Mediterranean colony

The pattern of chick feeding of the British storm-petrel Hydrobates pelagicus in a Mediterranean colony was examined by weighing chicks at 24-h intervals on different days during the nestling period. In order to calibrate daily mass increments (NET) against number of feedings, daily mass changes of chicks were regressed upon the sum of positive mass increments recorded overnight (SUM) during four nights. The average meal size delivered to chicks per night by one parent was 3.5 ß 1.3 g or 12% of adult weight. This was insufficient for sustaining constant chick mass during a day. On average 85% of chicks were fed each night, and the mean interval between feeds was 1.2 ß 0.5 nights. Nightly feeding frequencies differed among days, but this night-to-night variation was not related to meteorological conditions. Both food requirements necessary for chick body maintenance (zero-growth) and meal size were relatively constant for ages up to 59 days. However, feeding frequency decreased throughout the fledging period, accounting for agespecific variation in growth rates until fledging. Food requirement and feeding patterns at Benidorm were different from North Atlantic colonies. None the less, growth patterns were almost identical, suggesting adjustment to maintain chick body mass at a determined level, as food delivery to nestling appears to be regulated to chicks'nutritional requirements.     

Influence of weather on reproductive success of northern fulmars in the Canadian high Arctic

The northern fulmar (Fulmarus glacialis) is a common seabird of the North Atlantic Ocean, with breeding colonies broadly dispersed between 45°N and 80°N. At higher latitudes, breeding fulmars experience extensive sea-ice and presumably snow and low temperatures which do not affect fulmars in the southern part of the breeding range. We studied the relationship between weather and reproductive success of northern fulmars breeding at two colonies in the Canadian high Arctic. Collectively, hatching success, fledging success, and productivity (chicks fledged per egg laid) were similar between our study and results from colonies located south of the Arctic. However, a larger proportion of fulmars at apparently occupied sites (AOS) in high Arctic colonies appeared to forego egg-laying, resulting in lower proportions of chicks fledged per AOS. Extreme inclement weather was the major factor influencing nesting success, resulting in pulses of egg or chick loss during or immediately following major storms, although the mechanism of effects appeared to differ between the two colonies. For Arctic fulmars, the risks of nest failure due to stochastic, deleterious weather events may be offset by the predictable abundance of food supplies during chick-rearing in Arctic waters.     

The breeding biology and aspects of the feeding ecology of brown noddies Anous stolidus nesting near Culebra, Puerto Rico, 1985–1989

We have studied brown noddies Anous stolidus breeding on Cayo Noroeste in the Culebra National Wildlife Refuge for the past five years (1985–1989). Daily visits during our residence there each year permitted collection of precise data on arrival chronology, egg-laying and incubation patterns, egg morphometries, chick growth rates, food delivered to chicks and breeding success. Over 150 adults are now individually colour-banded, and each annual chick cohort has been uniquely marked. Some features of the breeding biology of Culebran brown noddies were similar to those reported for pairs at Atlantic and Pacific Ocean colonies; these included duration of egg development, mass of newly hatched chicks, chick growth rates and fledging periods. Other features appear unique to Culebra. These include a tightly synchronous arrival (range of first egg dates: 29 April-4 May) and short egg-laying period (about six weeks), a consistently high breeding success each year (average 84% hatching success, 88% chicks fledged from eggs hatched, 0.79 chicks fledged per pair), and an unusually narrow range of food items (two fish species) taken by adults for their own needs and those of chicks. Observations of the direction taken by adults departing the colony suggest a predictable and productive foraging area along a prominent east-west shelf-break located c. 20 km to the north. We conclude that during these five years, brown noddies on Cayo Noroeste were not limited by food during the breeding season.     

The 1992 epizootic of Newcastle disease in double-crested cormorants in North America

In the summer of 1992, morbidity and mortality in juvenile double-crested cormorants (Phalacrocorax auritus; DCC) attributable to Newcastle disease virus (NDV) was observed for the first time in seven northern USA states and one Canadian province, and recurred in three western Canadian provinces. Based on clinical signs and laboratory diagnostic findings, DCC mortality from NDV occurred in 59 of the 63 nesting colonies and two of three non-colony sites investigated. An estimate of in excess of 20,000 DCC died, with mortality rates ranging from < 1 to 37% in Great Lakes colonies to 20 to 92% in Minnesota (USA) and North and South Dakota (USA) colonies. Sick juvenile white pelicans (Pelecanus erythrorhynchos) exhibiting signs similar to sick cormorants, and dead pelicans were observed in Minnesota and North Dakota. Mortality rates in pelican colonies were as high as in the adjacent cormorant colonies, but no cause for the mortality of an estimated 5,000 pelicans was determined. No evidence of NDV was found in other species nesting in proximity to affected cormorants. Although the source of the NDV infection is unknown in cormorants, the simultaneous onset of the epizootics in juvenile birds over a wide geographic area implies that the virus was acquired by adults prior to migration and was carried back to nest sites, exposing susceptible nestlings. The possible transmission of this virus from free-ranging wild birds to domestic poultry is a concern. Based on repeated epizootics in cormorants since 1990, NDV seems to be established in DCC.     

Time‐lapse cameras reveal latitude and season influence breeding phenology durations in penguins

Variation in the phenology of avian taxa has long been studied to understand how a species reacts to environmental changes over both space and time. Penguins (Sphenicidae) serve as an important example of how biotic and abiotic factors influence certain stages of seabird phenology because of their large ranges and the extreme, dynamic conditions present in their Southern Ocean habitats. Here, we examined the phenology of gentoo (Pygoscelis papua) and chinstrap penguins (Pygoscelis antarctica) at 17 sites across the Scotia arc, including the first documented monitoring of phenology on the South Sandwich Islands, to determine which breeding phases are intrinsic, or rather vary across a species range and between years. We used a novel method to measure seabird breeding phenology and egg and chick survival: time‐lapse cameras. Contrary to the long‐standing theory that these phases are consistent between colonies, we found that latitude and season had a predominant influence on the length of the nest establishment, incubation, and guard durations. We observe a trend toward longer incubation times occurring farther south, where ambient temperatures are colder, which may indicate that exposure to cold slows embryo growth. Across species, in colonies located farther south, parents abandoned nests later when eggs were lost or chicks died and the latest record of eggs or chicks in the nest occurred earlier during the breeding period. The variation in both space and time observed in penguin phenology provides evidence that the duration of phases within the annual cycle of birds is not fundamental, or genetic, as previously understood. Additionally, the recorded phenology dates should inform field researchers on the best timing to count colonies at the peak of breeding, which is poorly understood.     

Mass stranding of wedge-tailed shearwater chicks in Hawaii.

Unusual numbers of wedge-tailed shearwater (Puffinus pacificus) chicks stranded on Oahu (Hawaii, USA) in 1994. Compared to healthy wedge-tailed shearwater (WTSW) chicks, stranded chicks were underweight, dehydrated, leukopenic, lymphopenic, eosinopenic, and heterophilic; some birds were toxemic and septic. Stranded chicks also were hypoglycemic and had elevated aspartate amino transferase levels. Most chicks apparently died from emaciation, dehydration, or bacteremia. Because many birds with bacteremia also had severe necrosis of the gastrointestinal (GI) mucosa associated with bacteria, we suspect the GI tract to be the source of disseminated bacterial infection. The identity of the bacteria was not confirmed. The daily number of chicks stranded was significantly related to average wind speeds, and the mortality coincided with the fledging period for WTSW. Strong southeasterly winds were a distinguishing meteorologic factor in 1994 and contributed to the distribution of stranded chicks on Oahu. More objective data on WTSW demographics would enhance future efforts to determine predisposing causes of WTSW wrecks and their effects on seabird colonies.     

Winter rainfall predicts phenology in widely separated populations of a migrant songbird

Climate change is affecting behaviour and phenology in many animals. In migratory birds, weather patterns both at breeding and at non-breeding sites can influence the timing of spring migration and breeding. However, variation in responses to weather across a species range has rarely been studied, particularly among populations that may winter in different locations. We used prior knowledge of migratory connectivity to test the influence of weather from predicted non-breeding sites on bird phenology in two breeding populations of a long-distance migratory bird species separated by 3,000 km. We found that winter rainfall showed similar associations with arrival and egg-laying dates in separate breeding populations on an east–west axis: greater rainfall in Jamaica and eastern Mexico was generally associated with advanced American redstart (Setophaga ruticilla) phenology in Ontario and Alberta, respectively. In Ontario, these patterns of response could largely be explained by changes in the behaviour of individual birds, i.e., phenotypic plasticity. By explicitly incorporating migratory connectivity into responses to climate, our data suggest that widely separated breeding populations can show independent and geographically specific associations with changing weather conditions. The tendency of individuals to delay migration and breeding following dry winters could result in population declines due to predicted drying trends in tropical areas and the tight linkage between early arrival/breeding and reproductive success in long-distance migrants.     

The diet of Common Guillemot Uria aalge chicks provides evidence of changing prey communities in the North Sea

Local differences in feeding conditions have been suggested as a cause of regional variation in seabird demography but multi‐colony comparisons of diet are rare. In UK waters the main fish eaten by seabirds during the breeding season belong to three families: Ammodytidae, Clupeidae and Gadidae. Climate change and fishing are affecting these fish stocks and so probably impact on predators such as seabirds. We used standardized observations of prey brought in for chicks to make the first integrated assessment of the diet of Common Guillemot Uria aalge chicks at a UK scale. Chick diet varied markedly among the 23 colonies sampled between 2006 and 2011. Sandeels (Ammodytidae), probably Lesser Sandeels Ammodytes marinus, were the commonest prey. Their contribution to the diet varied both latitudinally and among marine regions, with the proportion significantly higher for a given latitude on the west coast compared to the east. The non‐sandeel component of the diet showed latitudinal changes, with small clupeids, probably Sprats Sprattus sprattus, predominant at southern colonies whereas juvenile gadids were the main alternative to sandeels in the north. Comparison of our Guillemot chick diet with data collected 15–30 years earlier suggests that the proportion of sandeels in the diet has decreased at colonies bordering the North Sea. No significant change was apparent in Atlantic colonies but historical data were limited. The early years of our study coincided with a population explosion of Snake Pipefish Entelurus aequoreus in the Northeast Atlantic and North Sea. Pipefish were recorded in Guillemot chick diet at several northern and northwestern colonies in 2006 and 2007 but have been absent since 2009. Spatial and temporal variation in chick diet accorded broadly with patterns expected as a result of rising sea temperatures and impacts of fishing. Guillemot chick diet could potentially be a useful indicator of changes in the distribution and abundance of forage fish.     

Increased mortality of black-browed albatross chicks at a colony heavily-infested with the tick Ixodes uriae

At Bird Island, South Georgia, we studied the effects of the tick Ixodes uriae on survival of chicks at two colonies of the black-browed albatross Diomedea melanophrys, one where most chicks were infested with ticks, the other where most chicks were tick-free. When the two colonies were compared, it was found that the colony heavily-infested with ticks had significantly greater chick mortality than the colony lightly-infested with ticks. However, within each of the two colonies, there was no significant difference in survival between chicks with ticks and those without ticks.     

Mitochondrial evidence for panmixia despite perceived barriers to gene flow in a widely distributed waterbird

We examined the mitochondrial genetic structure of American white pelicans (Pelecanus erythrorhynchos) to: 1) verify or refute whether American white pelicans are panmictic and 2) understand if any lack of genetic structure is the result of contemporary processes or historical phenomena. Sequence analysis of mitochondrial DNA control region haplotypes of 367 individuals from 19 colonies located across their North American range revealed a lack of population genetic or phylogeographic structure. This lack of structure was unexpected because: 1) Major geographic barriers such as the North American Continental Divide are thought to limit dispersal; 2) Differences in migratory behavior are expected to promote population differentiation; and 3) Many widespread North American migratory bird species show historic patterns of differentiation resulting from having inhabited multiple glacial refugia. Further, high haplotype diversity and many rare haplotypes are maintained across the species' distribution, despite frequent local extinctions and recolonizations that are expected to decrease diversity. Our findings suggest that American white pelicans have a high effective population size and low natal philopatry. We suggest that the rangewide panmixia we observed in American white pelicans is due to high historical and contemporary gene flow, enabled by high mobility and a lack of effective physical or behavioral barriers.     

THE BREEDING OF THE GREATER FLAMINGO AND GREAT WHITE PELICAN IN EAST AFRICA

This paper brings together observations on the breeding of the Greater Flamingo Phoenicopterus ruber and Great White Pelican Pelecanus onocrotalus, mainly at Lake Elmenteita, Kenya, 1951–1971. The Greater Flamingo bred at Lakes Elmenteita and Nakuru in 11/21 observed years and at Lakes Natron and Magadi in 5/12 observed years. On average, it breeds about every second year, but a succession of breeding years is followed by several years in which no breeding occurs. A history of 21 years' breeding at Lakes Nakuru and Elmenteita is given. At Elmenteita three sites have been used, the main site in every breeding year, the others less often. The number of pairs breeding in any year has varied from 500–9,250, but in 1968 flamingos bred three times, involving perhaps 8,500 pairs which made about 15,700 nests, some pairs perhaps laying twice or even thrice in a year. Losses of eggs (38.2% overall) were caused by rising water (16.2%), competition for nest space with Great White Pelicans (6.9%, after 1968 only), human interference (3.5%), Marabou Stork predation (1.8%) and other natural causes (9.8%). Losses among chicks totalled 68.3% overall and were mainly due to Marabou Storks (36.5%), undiagnosed disease (8.6%), and rising water (6.6%). Disease caused serious loss only in 1966, and after 1968 losses from Marabous rose from 2.7% to 76.5%, resulting in an increase in overall mortality from 48.7 to 92%. This was perhaps associated with the establishment of a fish factory at Lake Naivasha. When attacking flamingo colonies Marabous did not actually eat many eggs or chicks, but simply caused wholesale desertion by alarming the flamingos. In 1968 total desertion of a colony of 4,500 pairs was caused between 18 and 26 March by a maximum of 17 Marabous, and similar wholesale desertion was caused in later years. The overall breeding success among Greater Flamingos at Elmenteita was about 19% of eggs laid, but without the excessive post-1968 Marabou predation would have been about 30%. At such a rate Greater Flamingos require at least 24 years of adult life to replace themselves, but if the mortality caused by Marabous since 1968 continues they will require about 58 years, and the population will inevitably decline. Breeding success at Lakes Magadi and Natron has been higher, about 44% of eggs laid; but figures available are much more approximate than at Elmenteita. Some new data on display, nest-site selection, laying dates, clutch-size, hatching and creche behaviour are given for the Greater Flamingo. The Great White Pelican bred at Lake Elmenteita from 1968 to 1971 without a break, some birds laying in every month, but with reduced laying November–December. They bred on the same islands as, and in association with the Greater Flamingo, and caused heavy losses among the latter, not through aggressiveness, but simply because of their superior size and weight. Although food supply must ultimately have controlled the pelican's ability to breed, an adequate food supply was available for 6 years before they did and continued after they had ceased. Their breeding was finally triggered by the Greater Flamingo colonies, with which the pelicans associated. When a flamingo colony was deserted because of Marabou Storks the pelicans, unafraid themselves of the Marabous, also deserted. They also associated with, and wiped out, a colony of Sacred Ibis. From July 1968 to June 1969 about 2,600 pairs of pelicans bred at Elmenteita, rearing about 2,200 young to the flying stage. The breeding colony apparently comprised most of the adults from Lake Nakuru and Lake Naivasha, the main feeding areas. From July 1968 to January 1971 certainly 7,200 and probably 8,000 pairs of pelicans bred at Elmenteita. Some pairs may have bred twice or thrice in this period. Breeding ceased suddenly in January 1971, eggs, and small and large young being alike abandoned for no established reason, although food supply was certainly still plentiful. Additional information on pair formation, incubation and fledging periods, nest-relief, etc. is given. The best available record of the incubation period is 35–36 days. Nest relief takes place on average about once every 48 hrs, and is dependent on thermal activity enabling the pelicans to soar. At Elmenteita large young ate quantities of putrefying matter, including the corpses of other young pelicans. They also ate living young hatching from eggs, and up to 14 days old. Touch probably plays an important part in helping them to locate possible food in opaque water.     

Sex-differentiated migration patterns, protandry and phenology in North European songbird populations

This study aims to investigate causes and mechanisms controlling protandrous migration patterns (the earlier breeding area arrival of males relative to females) and inter-sexual differences in timing of migration in relation to the recent climate-driven changes in phenology. Using standardised ringing data from a single site for eight North European migratory passerines collected throughout 22 years, we analysed sex-differentiated migration patterns, protandry and phenology of the entire populations. Our results show protandrous patterns for the first as well as later arriving individuals for all studied species. Males show more synchronous migration patterns compared to females and, hence, first arriving females followed males more closely than later arriving individuals. However, we found no inter-sexual differences in arrival trends as both sexes advance spring arrival over time with the largest change for the first arriving individuals. These findings seem in support of the “mate opportunity” hypothesis, as the arrival of males and females is strongly coupled and both sexes seem to compete for early arrival. Changes in timing of arrival in males and females as a response to climatic changes may influence subsequent mating decisions, with subsequent feedbacks on population dynamics such as reproductive success and individual fitness. However, during decades of consistent earlier spring arrival in all phases of migration we found no evidence of inter-sexual phenological differences.     

Long-term changes in breeding phenology at two seabird colonies in the western North Sea

There is compelling evidence that the breeding phenology of many species has changed substantially in recent decades. However, taxonomic and spatial variation in the direction and rate of change is still not well understood. We explored these issues by analysing a dataset containing information on first egg dates of 10 species of seabird at two major breeding colonies (86 km apart) in the western North Sea over a period of 35 years. Within a species, timing of breeding was positively correlated between the two colonies, suggesting that factors affecting the phenology of these species operated at a regional rather than a colony scale. Comparison of time trends among the species revealed contrasting patterns, with some showing no systematic change, others becoming earlier and others later. The clearest species groupings appeared to be among the terns with arrival and/or first egg dates becoming earlier in Arctic Terns Sterna paradisaea , Common Terns Sterna hirundo and Sandwich Terns Sterna sandvicensis , and among the auks (Common Guillemot Uria aalge , Razorbill Alca torda and Atlantic Puffin Fratercula arctica ) and Black-legged Kittiwake Rissa tridactyla where the trend was in the opposite direction towards later breeding. This general trend towards later breeding in the latter group of species contrasts with correlational evidence from many other organisms indicating that breeding phenology is advancing in response to climate change.     

Reproductive measures and chick provisioning of Cory's Shearwater Calonectris diomedea borealis in the Azores

Capsule Timing of breeding influenced wing-length at fledging, and egg size may be an indicator of fledging weight and the amount of food received by chicks.

Aims To investigate chick growth, temporal patterns of chick food provisioning and the importance of indices of parental condition or quality, egg size and hatching date, to predict nestling body mass and wing-length at fledging, and compare breeding and chick feeding characteristics between colonies in the northeast Atlantic.

Methods A survey of Cory's Shearwater nests was carried out at Vila islet. A sample of 52 chicks, ringed and weighed at hatching, was selected to study chick growth and food provisioning.

Results Hatching success (51%) was much lower than fledging success (87%). Both hatching date and egg size contributed to explain wing-length at fledging, but hatching date, which was negatively correlated with wing-length at fledging, had the most important contribution (22%). There was some indication that egg size may explain variation in fledging weight and the amount of food received by chicks. Food delivery and feeding frequency of chicks varied throughout the chick development stage and three phases were distinguished: (1) 0–29 days, the highest feeding frequency values and a linear increase in food delivery; (2) 30–69 days, an oscillation in food delivery and medium feeding frequencies; (3) 70–90+ days, a sharp decrease in both food delivery and feeding frequency.

Conclusion Variation in food availability did not seem sufficient to override the overall importance of indices of parental quality in determining reproductive measures and chick provisioning. Breeding and feeding characteristics were similar between colonies in the northeast Atlantic, with variability in chick provisioning higher further south.     

Climate Change Increases Reproductive Failure in Magellanic Penguins

Climate change is causing more frequent and intense storms, and climate models predict this trend will continue, potentially affecting wildlife populations. Since 1960 the number of days with >20 mm of rain increased near Punta Tombo, Argentina. Between 1983 and 2010 we followed 3496 known-age Magellanic penguin (Spheniscus magellanicus) chicks at Punta Tombo to determine how weather impacted their survival. In two years, rain was the most common cause of death killing 50% and 43% of chicks. In 26 years starvation killed the most chicks. Starvation and predation were present in all years. Chicks died in storms in 13 of 28 years and in 16 of 233 storms. Storm mortality was additive; there was no relationship between the number of chicks killed in storms and the numbers that starved (P = 0.75) or that were eaten (P = 0.39). However, when more chicks died in storms, fewer chicks fledged (P = 0.05, R ² = 0.14). More chicks died when rainfall was higher and air temperature lower. Most chicks died from storms when they were 9–23 days old; the oldest chick killed in a storm was 41 days old. Storms with heavier rainfall killed older chicks as well as more chicks. Chicks up to 70 days old were killed by heat. Burrow nests mitigated storm mortality (N = 1063). The age span of chicks in the colony at any given time increased because the synchrony of egg laying decreased since 1983, lengthening the time when chicks are vulnerable to storms. Climate change that increases the frequency and intensity of storms results in more reproductive failure of Magellanic penguins, a pattern likely to apply to many species breeding in the region. Climate variability has already lowered reproductive success of Magellanic penguins and is likely undermining the resilience of many other species.     

Parental attendance and squatting in the Kittiwake Rissa tridactyla during 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 North Atlantic and Alaskan colonies. This reflected the flexibility of adult behaviour in relation to brood size and food availability.     

Use of Implanted Radiotransmitters to Estimate Survival of Greater Sage-Grouse Chicks

ABSTRACT Reduced chick survival has been implicated in declines of greater sage-grouse (Centrocercus urophasianus) populations. Because monitoring survival of unmarked sage-grouse chicks is difficult, radiotelemetry may be an effective technique to estimate survival rates, identify causes of mortality, and collect ecological data. Previous studies have used subcutaneous implants to attach radiotransmitters to hatchlings of several species of birds with precocial young. Previous researchers who used subcutaneous implants in free-ranging populations removed chicks from the capture location and implanted transmitters at an alternate site. Because logistics precluded removing newly hatched greater sage-grouse chicks from the field, we evaluated a method for implanting transmitters at capture locations. We captured 288 chicks from 52 broods and monitored 286 radiomarked chicks daily for 28 days following capture during May and June 2001–2002. Two (>1%) chicks died during surgery and we did not radiomark them. At the end of the monitoring period, 26 chicks were alive and 212 were dead. Most (98%, 207/212) radiomarked chick mortality occurred < 21 days posthatch and predation (82%, 174/212) was the primary cause of death. Necropsies of 22 radiomarked chicks did not indicate inflammation or infection from implants, and they were not implicated in the death of any chicks. Fate of 48 chicks was unknown because of transmitter loss (n = 16), radio failure (n = 29), and brood mixing (n = 3). Overall, the 28-day chick survival rate was 0.220 (SE = 0.028). We found that mortalities related to the implant procedure and transmitter loss were similar to rates reported by previous researchers who removed chicks from capture sites and implanted transmitters at an alternate location. Subcutaneous implants may be a useful method for attaching transmitters to newly hatched sage-grouse chicks to estimate survival rates, identify causes of mortality, and collect ecological data.     

Brood reduction in temperate and sub-tropical ospreys

Summary In an effort to understand patterns and causes of nestling loss in Ospreys (Pandion haliaetus), I studied brood reduction in three eastern U.S. Osprey colonies during 1978 and 1979. The colonies, located in Florida Bay (1) and on coastal Long Island, N.Y. (2), differed in the average daily amount of food delivered to nestlings; Florida nests received 43% and 11% less fish per day than nests in the two N.Y. colonies, largely because latitude and season restricted day length and thus foraging time for the winter-breeding Florida Ospreys. Increased distance from stable food sources accounted for the lower rate of feeding at one of the N.Y. colonies. Variation in clutch size in the three colonies reflected differences in latitude more than in food availability; average clutch sizes in Long Island were larger than Florida clutches by 0.5 of an egg, but were similar to each other and to those in other northeastern U.S. Osprey populations.Increased nestling loss coincided with reduced food delivery rates and, in food stressed colonies, this loss was 2–3 times greater than any recorded for Ospreys. Starvation was the primary cause of nestling death, with mortality concentrated on third chicks, which hatched on average 3.9 d later and from eggs 5.6% smaller than chicks hatching first. Sibling aggression accounted for the preferential feeding of older nestmates,but only in colonies or nests where food was limited. Aggressive chicks nearly always stopped fighting after being fed. This behavior provided a reversible mechanism for controling brood reduction that was based on nutrition. Growth rates of young measured during the first half of the growth period were more variable between colonies than within nests. This is interpreted as reflecting both the differences in colony food delivery rates as well as the evolutionary pressures of sibling competition to equalize the growth of nestmates.     

Are Morphometrics Sufficient for Estimating Age of Pre-Fledging Birds in the Field? A Test Using Common Terns (Sterna hirundo)

Age is a key component of fitness, affecting survival and reproductive capacities. Where it is not possible to study known individuals from birth, morphometrics (predominantly patterns of plumage development for birds) are most often used to estimate age. Although criteria for age estimations exist for many species, the degree to which these criteria improve the precision of estimates remains to be tested, restricting their widespread acceptance. We develop a photographic tool for estimating ages of Common Tern (Sterna hirundo) chicks and test it using 100 human observers of varying prior experience across four breeding colonies (three North American sites and one European site) and under controlled laboratory conditions. We followed the design approach of other morphometric tools, expanding it to create a user-friendly guide (divided into six age groupings). The majority (86%) of observers improved in chick-aging accuracy when using the tool by an average of 20.1% (±1.4 SE) and correctly estimated 60.3% (±1.4) of chick ages. This was similar to the intrinsic aging ability of our best field observer (63.3%). Observers with limited experience showed the greatest increases in chick-aging accuracy over experienced observers who likely had established a method for estimating chick ages prior to using the tool. Even the best observers only correctly estimated ages of chicks 62.9% (±2.8) of the time in the field and 84.0% (±2.9) of the time in the lab when using the tool and typically underestimated ages. This indicates that developmental variation between individual chicks can prevent completely reliable age estimates and corroborates the few existing data that suggest that morphometric criteria fail to achieve robust levels of accuracy and may introduce error into studies that rely on them. We conclude that novel approaches for estimating age, not only morphometric criteria, must be pursued.