Results
Detection probabilities
The mean of all seven detection probabilities (manual detections from
years 1, 2 and 3, MARK detections from years 1, 2 and 3, and detection
from radio-tagged birds in year2) was 0.33 (se = 0.02); the probability
of detecting a Whitethroat at our study site when it is present was once
every three visits (Fig. 1). Detection probabilities were similar
between years when undertaken manually (mean = 0.36, se = 0.02,F (2,48) = 0.13, p = .88) and in MARK (mean
= 0.29, se = 0.03, F (2,48) = 1.48, p =
.24) and were similar across methods during all three years (year1:t (38)= 0.88, p = .38; year2:F (2,32) = 2.44, p = .10; year3:t (28)= 1.18, p = .25).
Site persistence
Site persistence, defined as the number of days an individual was
present and detected in the area, varied widely across individuals,
ranging from one day to 165 days (mean = 31 days, se = 3 days, n= 341) but did not seem to differ significantly between years and
between adult female and male birds (Table 2). First-years, however,
remained for significantly shorter periods when compared to adults
(Table 2).
Between-years site
fidelity
Return rates
Overall return rates were similar across years but varied between age
groups dependent on year and residency category, with more long-term and
short-term winter residents returning than passage birds. A similar
proportion of individuals returned between years (χ2 =
0.56, df = 1, p = .45): 36/182 (20%) individuals returned from
year1 to year2 (group A), and 24/145 (17%) individuals returned from
year2 to year 3 (group B). Seven individuals from year1 failed to return
in year2 but then returned in year3 (group C). Only 12 individuals were
seen during all three fieldwork seasons. In group A, a similar
proportion of individuals of adults and first-year birds returned the
following year: 13/62 (21%) adults and 22/96 (23%) first-years
(χ2 = 0.08, df = 1, p = .77). In group B,
however, there were clear differences between individuals of different
ages: 20/90 (22%) adults and 3/50 (6%) first-years returned
(χ2 = 6.16, df = 1, p = .01). Most individuals
from group C were first-year birds in year1. Female and male adults had
similar return rates in group A (females = 5/21, 24%, males = 6/28,
21%; χ2 = 0.04, df = 1, p = .84) and in group
B (females = 9/35, 26%, males = 8/42, 19%; χ2 =
0.49, df = 1, p = .48). When comparing return rates amongst
residency categories in group A, long-term winter residents (14/43,
33%) and short-term residents (2/7, 29%) had higher return rates than
passage birds (10/90, 11%) (χ2 = 9.34, df = 2,p = .009). A similar trend was seen in group B
(χ2 = 6.98, df = 2, p = .03); 12/31, 39% of
long-term winter residents returned; 3/16, 19% short-term residents;
5/40, 13% passage birds.
The distance moved from one year to another varied among individuals
(Fig. 2) but, on average, individuals moved less than 300 meters (Fig.
2; Appendix 2). This figure was similar amongst groups A, B, and C
(F(2,51) = 0.006, p = .99).
The distance shifted between years did not vary significantly according
to previous age (F(1,45) = 2.1, p = .16), sex
(F(1,33) = 0.58, p = .45) or previous residency
(F(2,47) = 1.61, p = .21; Fig. 3; Appendix 2).
Results from the averaging model, however, show that first-years in
group A (seen form year1 to year3) shifted longer distances than adults
(Table 2). All other variables were NS (Table 2).
Residency repeatability
The degree of residency category
repeatability, i .e . whether individuals remained in the
same residency category through different years, varied across
individuals (Fig. 4). 68% of long-term winter residents remained as
such the following year, and 32% remained for similar or shorter
periods. Most of the short-term winter residents (66%), when they
returned the following year, were categorised as passage birds, 17%
remained for similar periods and 17% remained for longer. Half of the
passage birds remained as such the following year, while the other half
remained for longer periods: 31% were categorised as long-term winter
residents and 19% as short-term winter residents (Fig. 4).
When comparing the duration (in days) spent at the site of individuals
from one year to another, we found that there was a significant somewhat
positive correlation between the duration in year i and the
duration in year i +1 (correlation R = 0.32, p = .026):
individuals that remained for longer periods in year i remained
longer periods in year i +1 but, overall, individuals remained for
shorter periods the following year (Fig. 5). The latter is especially
true for short-term and long-term winter residents. Passage birds,
however, remained longer periods during year i +1 compared to
during year i (Fig. 5).
Departure dates
Departure dates for individuals seen between January and April during
years 1 and 2 did not vary between years (F(1,179) =
0.02, p = .90), between adults and first-years
(F(1,179) = 0.002, p = .89), or between males and
females (F(1,137) = 0.03, p = .31). Individuals
that were seen during at least two years showed relatively low
repeatability values (r = 0.15, Table 3). The difference (in
days) between the departure date in year i that of yeari +1 was statistically significant when categorising individuals
by their residency at year i (F(2,37) = 4.3,p = .02). This means that
long-term birds
departed at more similar dates
across years compared to passage birds (Table 3). When categorising
individuals by their previous age, we found that there was no
significant difference in departure dates between adults and first-year
birds (F(1,37) = 0.27, p = .61).