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Winter in Europe vs Africa enhances juvenile survival (Rotics et.al. 2017)
Winter in Europe vs Africa enhances juvenile survival (Rotics et.al. 2017)
Abstract
cause and implication of migration change by behavior and survival
EU compared to Africa
movement and foraging range:arrow_down:
flying time:arrow_down: resting time :arrow_up: use less energy :arrow_down:
foraging effort :arrow_down:
EU bird hatch later
:red_flag:But hatch late itself did not yield survival benefit, not all late hatch chick shorten migration
winter in EU is less demanding may explain
In this study EU bird survival better
Introduction
Plasticity
allow bird respond to the changes by altering time ad routes
:red_flag: studies reported shortening migration, new winter site, increase number, probably due to food and milder winter increase bird
survival
. condition in winter site :arrow_right: survival :arrow_right: population dynamics
:warning: winter close to natal ground have better survival, spoonbill, flamingo,Egyptian vultures and red kites. So do white stork
:question:Africa survival high, because most storks still do
:question:Europe high, recent growing implies a survival benefit. along with low cost (flight) and risk (predation, hunting)
Further
examined why some in Europe some in Africa
:question: late-hatching juveniles less fit for migration, more likely to shorten
Methods
Tag methods,total 92, 54 until October (winter start)
duty cycles
EU 6, Africa 48, October to December, GPS-ACC high resolution date.
Sub-sample Africa data
because Europe daylight is shorter, half hour before and after were extracted
:warning: Survival, first year, binary
death: most more than five days no move in a buffer of 75m, or tag retrieved.
:red_flag:missing, no other indication of mortality
:red_flag:
18 months of missing, 90% death, in line with estimated tag malfunction rate
:red_flag:
or omit the miss bird
Movement
daily displacement distance DDd: two consecutive roosting location at 2:00 GMT
Stationary days: within 10km DDd. large-progression days: more than 50km DDd
daily distance DD: accumulated distance
foraging utilization area: only daytime nonflight(speed < 5m/s), 90% r-LoCoH
Energy and behavioral parameters: ODBA and behavior classify
land use, ambient temperature
landfill use: visual identification in google earth
Hatching date, migration onset and pre-migration experience
used regression to estimate hatch date
onset date:
first date more than 100km southwards
pre-migration:1
fledgling date is 2 consecutive days away from nest >100m at least 20mins
2 total pre-migration flight time
number of records that speed >5m/s with 5 min sampling rate
Statistical analysis
:red_flag:data transform and normal test
EUW and AFW comparisons: t test and Wilcoxon rank sum
:red_flag:
GLM(wintering site~hatching date+migration onset, link=binomial)
:red_flag:
GLM(survival~migration onset)
Ethical
Results
:red_flag: Survival：54 survival till October, all EUW alive and AFW 38.2% (omit missing) or 29.2% (90% missing dead)
Fisher exact test
Movement EUW:
DDd and DD both shorter
higher stationary days, lower ratio of large-progression days
small UD area
ODBA and behaviour: EUW
lower ODBA, likely flew less, rested more, foraging time not differ,
t test
lower foraging ODBA
Land use and ambient temperature: EUW
:warning: more cropland,
three use landfill, spand 38% total daylight time and 40% foraging time inside or less than 100m
lower temperature
Factors affecting wintering location
:warning: EUW hatch later, started migrating later.
migration onset most important to determine the winter site BUT not influence survival GLM AIC, model with all factor or separately, Wald x1^2
:warning: age at migration onset not different, nor pre-migration experience
Discussion
overwinter in EU attained higher survival (like flamingo, spoonbill). but
our data revealed multiple behavioural and energetic differences that associated with higher survival
EUW more localized, movement reduced, foraging smaller, flight less, resting more, consequently ODBA low.
"Correspondingly, reduced energy while curtailing migration have also been reported Flack et. al. 2016"
:warning: EUW foraging energy less, more at human-related habitat (agricultural areas and landfill). fitness benefits
some weakness of study
:red_flag:
"Nevertheless, we suggest that reduced activity-related energetic costs while wintering in Europe through utilization of anthropogenic resources could be a significant cause of the EUW storks' elevated survival rates"
:!?:
"Survival could also be affected by differences in the movement patterns, regardless of their energetic cost. Distance :arrow_up: risk and difficulties involved in reaching new and unfamiliar environments :arrow_up: "
AFW
carry over effect
from long distance migration,
predation and hunting
but
"we cannot separate the contribution "
:warning: in the light of Schaub et.al 2005 NDVI Africa WS survival:
foraging cost, energy expenditure, habitat use
seem highly relevant to juvenile stork survival
who winter in EU
:warning: hatch late and migrate late BUT we suggest the
social cues
, failed to join the group.
EUW also unusual of frequent stopover during migration
:warning: paradox of late hatch survive better
:red_flag: normal late hatch lower survival
:warning:
"Our results do not associate late hatching itself with increase survival, but rather, it may have a surprisingly advantageous outcome only under specific circumstances of staying in Europe. "
:!:
:warning: Spain stork
"
Juvenile survival
was found to be
more important
than breeding output in
regulating the population
size of storks and black kites. (Schaub et.al. 2005; Sergio et.al. 2011)."
:warning:
High juvenile survival" contributes to the EU overwinter storks, also
involved of shortening migrations** :!:
"Previous studies elucidated
overwintering conditions
as the most important determinants of population dynamics"
:warning:
Africa sub-optimal ?
Maybe just for first year
:!:
survival benefits may restricted to juveniles or even reversed :!?:
similar paradox
:red_flag:Spoonbill:
evolutionary gap of actual and optimal behavior
in stork could maintained by social cues
4/6 EUW migrated to Africa suggest
NO Genetic basis
:warning:
"if gap exists, plastic nature of bird is expected to lead to a decrease in long-distance migratory behaviour"
:red_flag:Caution with draw conclusion of our case study