ANNUAL RETURN RATES OF BREEDING GRASSLAND SONGBIRDS

2007·4.1 MB·English

by  Stephanie L Jones

The Wilson Journal of Ornithology 1 l9(l):89-94, 2007
ANNUAL RETURN RATES OE BREEDING
GRASSLAND SONGBIRDS
STEPHANIE L. JONES,' J. SCOTT DIENI,^ MICHAEL T GREEN,^ AND
PAULA GOUSE^'
J.
—
ABSTRACT. We used reobservation of color-banded birds to index annual breeding site fidelity of four
species of songbirds that nest in the northern mixed-grass prairie of northcentral Montana (1996-2005). Terri-
torial males of Sprague’s Pipits (Anthiis spragueii), and Savannah (Passerculiis sanchvichensis). Grasshopper
{Ammodramussavannariim), and Baird’s {A. hairdii) sparrows were locatedon hve permanentstudy sites{1998-
2004) and lured into mist-nets using tape broadcasts ofconspecihc songs and calls. The proportion reobserved
was 5.3% (/? = 247) across all banded adult males. Grasshopper Sparrows had the highest proportion ofreturns
(8.9%), followed by Savannah Sparrows (5.4%), Baird’s Sparrows (5.1%), and Sprague’s Pipits (2.1%). Three
nestling Savannah Sparrows were reobserved in subsequent years (n = 193), while no nestlings of the other
species were reobserved {n = 401). Our return rates were low for all adults in comparison with typical reports
of return rates for songbird species of woodland and shrubland habitats. Migratory nomadism may explain this
phenomenon, where grassland migrants are opportunistic in site selection, rather than faithfully returning to
potentially uninhabitable former breeding sites. Received20 December 2005. Accepted 9August 2006.
Breeding site-fidelity is defined as the ten- namic environments with fluctuating condi-
dency of a migratory bird to return to a pre- tions that, depending on scale and feature, are
vious breeding site. Numerous studies have unpredictable in time and space, creating a
documented strong breeding site-fidelity in mosaic of habitat conditions (Ahlering 2005,
some migratory birds (Gavin and Bollinger Winter et al. 2005). This variability is due to
1988, Green 1992, Murphy 1996, Porneluzi many causes, including effects of lightning-
2003), especially for those species that nest in and human-set fires (Higgins 1984), intense
shrubland and forested habitats (Porneluzi and grazing by prairie dogs {Cynomys spp.), bison
Faaborg 1999, Gardali et al. 2000). The return {Bison bison), and other ungulates (Kirsch and
of migratory birds to earlier breeding sites Kruse 1973) and, perhaps most importantly,
demonstrates remarkable orientation and sug- widely fluctuating precipitation levels across
gests strong evolutionary benefits to returning years (Igl and Johnson 1999, Ahlering 2005).
to the same area to breed, particularly when Alternating periods of drought and above-av-
successful breeding has occurred at a site in erage precipitation result in fluctuations in the
the past (Gavin and Bollinger 1988, Porneluzi structure and floristics of grasslands, within
2003). However, the potential benefits of re- and between years (Winteret al. 2005). Strong
turning to previously successful breeding sites annual variation in breeding habitat conditions
could be negated if nesting habitat is highly can cause tremendous shifts in local and re-
variable from year-to-year, possibly becoming gional bird population densities (Fretwell
unsuitable in some years. 1986, Igl and Johnson 1999, Winter et al.
Grasslands of the northern prairies are dy- 2005). Evidence suggests that some grassland
birds have adapted to this variability by ex-
DF'CU,.SD.enFviesrh,aCnOd W8i0l2d2l5i,feUSSeAr.vice, P. O. Box 25486 hibiting low site fidelity, often resulting in
^Redstart Consulting, 403 Deer Rd., Evergreen,CO spectacular fluctuations in local population
80439, USA. densities (Cody 1985, Igl and Johnson 1999,
^U.S. Fish and Wildlife Service, 911 N.E. 11th Winter et al. 2005). Many grassland bird spe-
Ave., Portland, OR 97232, USA. cies have evolved nomadic strategies for
WUiSl^AdUl..iSf.e RPeifshugaen,dHWCild6l5,ifBeoSxer5v7i0c0e,, BMaolwtdao,iMnTNa5t9i5o3n9a,l bmraekeedsinigt psoitteensteilaelcltyiounnpsroifnicteabhlaeb,iteatveinnsftoarbiplriet-y
^Corresponding author; e-mail; viously successful nesters, to return consis-
[email protected] tently to the same grassland breeding areas
89
90 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 119, No. 1, March 2007
(Andersson 1980). Nomadism is defined as 1.3-10.1 km apart, comprising 218 ha of flat
the tendency of adults and juveniles to move to gently rolling native mixed-grass prairie.
widely in response to resources that are patchy Blue grama (Bouteloua gracilis), needle-and-
in time and space (Andersson 1980, Johnson thread (Stipa comata), western wheatgrass
and Grier 1988). Nomadic behavior is a se- (Pascopyrum smithii), and dense clubmoss
lectively advantageous alternative to site-fi- {Selaginella densa) were the dominant her-
delity for grassland birds (Cody 1985), and is baceous species. Shrubs were sparse and trees
indicated by relatively low return rates, when absent. Bowdoin NWR has not been grazed
compared with return rates ofbirds inhabiting by cattle for >29 years. One study site was
more stable environments (e.g., shrublands partially burned in 1994 and one site was pre-
and forests). scribed burned in 2000; otherwise, no burning
Site fidelity studies of grassland bird pop- events have occurred since refuge documen-
ulations are largely restricted to eastern tation began in 1936.
North America. Sedge Wrens (Cistothorus Capture and Marking.—Known territorial
platensis, Herkert et al. 2001), Henslow’s adult males were lured into 30- or 36-mm
(AmmocIramus henslowii, Herkert et al. mesh mist nets using tape playback recordings
2002), Le Conte’s (A. leconteii, Murray of conspecific song beginning in 1998 (Sogge
1969), and Nelson’s Sharp-tailed (A. nelsoni, et al. 2001). We used Sony TC-D5Pro II or
Murray 1969) sparrows all had return rates Marantz PDM 430 cassette recorders ampli-
that were lower (<13.5%) than those typi- fied by an AmpliVox s805 Multimedia Am-
cally reported for woodland and shrubland plifier, connected into two tweeters by 30-50
nesting passerines. However, Bobolinks m of 16-gauge speaker cord. Speakers were
{Dolichonyx oryzivorus), whose return rates placed on either side ofa 12-m mist net within
varied from 44 (n = 85) to 70% (/? = 79) for the territory of a target male. Tape playback
adult males (Gavin and Bollinger 1988, Bol-
of conspecific song was broadcast to draw the
linger and Gavin 1989, Martin and Gavin
target male into the net. Carved wooden de-
1995), have return rates that are more com-
coys were placed at the net as visual lures
mensurate with shrub and forest dwelling
beginning in 2003.
species (Green 1992). Dickcissel (Spiza
Each individual captured was marked with
americana) also showed a tendency to return
a uniquely numbered federal aluminum band,
to former breeding sites in the center of their
plus three color bands whose colors were ran-
range (Fretwell 1986), with a return rate of
49% (/? = 82) in Kansas (Temple 2002). domly selected. Sprague’s Pipits were banded
We investigated breeding songbird site fi- with a year cohort color band, and a color
band denoting gender and age. Incidental fe-
delity in the mixed-grass prairie of northcen-
tral Montana. Four co-occurring species were males captured at the net were also banded.
Nestlings were banded, beginning in 1996,
studied: Sprague’s Pipits (Ant/ius spragueii),
and Savannah {Passerciilus samhvicheusis). with a year cohort color; processing occurred
Grasshopper {Ammodramus savanmirum), and on day 7 or 8 post-hatch (Dieni and Jones
Baird’s (A. hairdii) sparrows. Data on grass- [2003] describe nest searching methods). Gen-
land birds in the northern Great Plains are rel- der for adults was assigned based on the pres-
atively scarce; no other return rate studies ence of a cloacal protuberance for males or
have been published on Sprague’s Pipits with brood patch for females; gender of hatching-
only one study on Baird’s Sparrows (Green year birds c—ould not be assigned.
1992). Returns. Field assistants identified the
banding status of all observed individuals
METHODS
among target species during nest searching ac-
Study Area.—Our study was conducted at tivities from May to August 1997-2005. All
Bowdoin National Wildlife Refuge (NWR) in individuals ofthe target species were checked
Phillips County, northcentral Montana (48° for bands either by capture ofterritorial males
24' N, 107° 39' W; -750 m elevation). Data or visually using binoculars and spotting
were collected during summers of 1996-2004 scopes on all study sites. In addition, the tar-
on five permanently located sites (26-59 ha) get species were also visually observed, or oc-
Jones et al. • RETURN RATES OF GRASSLAND SONGBIRDS 91
TABLE 1. Grassland bird banding at Bowdoin National Wildlife Refuge, Montana. Adult male banding
effort from 1998 to 2004, nestlings (gender unknown) 1996-2004, returns 1997-2005.
No. banded No. returned %
Species Adults Ne.stlings Adults Nestlings Adults Nestlings
Sprague’s Pipit 48 160 1 0 2.1 0.0
Savannah Sparrow 37 193 2 3 5.4 1.6
Grasshopper Sparrow 45 138 4 0 8.9 0.0
Baird’s Sparrow 117 103 6 0 5.1 0.0
Totals 247 594 13 3 5.3 0.5
casionally captured off-site throughout Bow- technique was effective in capturing territorial
doin NWR. adult males of all target species. Using the
Male Sprague’s Pipits were generally de- number of nests located as an index to terri-
tected only during territorial displays that oc- tory abundance, our capture ratio of adult
curred 50-100 m above the ground (Robbins males to number ofknown nests was less than
1998). Thus, reobservation required either re- one for Savannah Sparrows (0.24), Sprague’s
capture or luring individual males within Pipits (0.62), and Grasshopper Sparrows
viewing distance using tape playback of con- (0.63). However, our capture ratio exceeded
specific song. We also were able to reobserve unity for Baird’s Sparrows (2.6), which sug-
individual Sprague’s Pipits in nests monitored gests that our sample may have included tran-
with miniature video cameras (SLJ and PJG, sients, as well as individuals whose nesting
unpubl. data). attempts had failed earlier in the season.
We assumed no significant effect of cap- We banded Savannah Sparrow nestlings (/z
ture, handling, or bands on return rates; to = 193) of which 1.6% were reobserved in
our knowledge, there were no capture-related subsequent years; no banded nestlings were
injuries or mortality. Similar techniques did re-sighted among the other target species {n
not negatively affect return rates of female = 401) (Table 1). Two of the reobserved Sa-
Wood Thrushes (Hylocichia miistelina), in- vannah Sparrow nestlings were identified to
cluding hatching-year birds (Perkins et al. individual; one was observed at its natal site,
2004). Analysis of the use of colored bands and one was reobserved 4.8 km from its natal
(most ofthe same colors that were used here) site. Ten female Savannah Sparrows were cap-
on a migratory population ofAmerican Gold- tured incidentally at the net. Among these, one
finches {Carduelis tristis) showed that color adult female returned two consecutive years
bands did not appear to affect return rates post-capture to the same site.
(Watt 2001).
DISCUSSION
RESULTS
Three patterns of breeding-ground settling
—
Return Rates Thirteen banded adult males have been described for upland grassland wa-
.
were reobserved (5.3%, n = 247) (Table 1). terfowl, characterized as homing, opportunis-
Grasshopper Sparrows had the highest pro- tic, and flexible (Johnson and Grier 1988).
portion ofadult male returns (8.9%), followed Homing, where adults return to the same
by Savannah Sparrows (5.4%), Baird’s Spar- breeding area used before, is thought to be a
rows (5.1%), and Sprague’s Pipits (2.1%) (Ta- response to relatively stable and ostensibly
ble 1). Ten of the 13 reobserved adult males more predictable habitats. Opportunistic set-
were confirmed to have returned to the same tling, where the individual settles in the first
site where they were originally captured. The suitable site encountered in its breeding range,
remaining three (one each for Sprague’s Pipit, regardless ofconditions in former breeding ar-
and Grasshopper and Baird’s sparrows) could eas, is generally thought to be a response to
not be identified to individual and we were less stable (less predictable) habitats. Flexible
unable to identify—their sites of origin. settling is where the individual will return to
Capture Effort. Our targeted mist-netting an area used previously, but moves elsewhere
92 THE WILSON JOURNAL OL ORNITHOLOGY • Vol. 119, No. 1, March 2007
if that area has become unsuitable. Opportu- returning to Fort Riley in Kansas (B. K. San-
nistic or flexible settling would be expected to dercock, pers. comm.), while no banded adults
occur more frequently in endemic grassland orjuveniles (n = 85) were reobserved during
birds than homing as an evolutionary response a five-year study on Arapaho Prairie, a mixed-
to habitat variability inherent in grasslands. grass prairie in the Sandhills of Nebraska
Indeed, many grassland bird populations un- (Kaspari and O’Leary 1988).
dergo considerable annual changes in distri- Our relatively low reobservation rates sug-
bution and abundance in the northern Great gest three possibilities; (1) low probability of
Plains (Johnson and Grier 1988, Shane 2000, reobservation of banded individuals, (2) low
Herkert et al. 2001, Green et al. 2002). survivorship, and (3) low site-fidelity. Reob-
Annual return rates for all species reported servation ofadults on-site was straightforward
here suggest low site fidelity. Reviews ofstud- and not problematic, although only limited
ies ofwoodland and shrubland migratory pas- time was spent searching adjoining areas for
serines reported a mean return rate of ~ 46% banded individuals. We were unable to cal-
for adults (Green 1992, Johnson and Geupel culate meaningful survivorship estimates us-
1996, Gardali et al. 2000). Our study is con- ing mark-recapture statistics since our return
sistent with a return rate of 5.3% (n = 95) rates were too low (Murphy 1996). Therefore,
reported for Baird’s Sparrows in North Dakota either our survival was much lower than rates
(Green 1992). Moreover, it has been suggested typically estimated for passerines, which
that lack ofgeographic variation in bird songs seems unlikely, or our return rates were ac-
(e.g., Baird’s Sparrows) may also indicate an tually low and many of the adults that did not
opportunistic settling pattern, since regional return moved to new breeding sites. Discount-
dialects would have difficulty forming in pop- ing low reobservation and survivorship, our
ulations with substantial between year mixing results indicate a nomadic migratory pattern
(Kroodsma and Verner 1978, Green 1992, for our study species, suggesting opportunistic
Kroodsma et al. 1999). or flexible settling patterns, indicative of spe-
Our data are inconsistent with some reob- cies adapted to historically unstable breeding
servation data for Savannah and Grasshopper habitats (Owens and Myers 1973, Andersson
sparrows from other geographic regions of 1980, Johnson and Grier 1988). However, we
their respective breeding ranges (Bedard and cannot ignore the fact that some of our birds
LaPointe 1984, Wheelwright and Rising 1993, returned to our sites to breed; indeed. Green
Vickery 1996). Multiple studies of Savannah (1992) also found that a small number of
Sparrows in eastern North America showed a Baird’s Sparrows returned and bred in the
mean return rate of46.1% (SLJ, unpubl. data), same territories in subsequent years. This sug-
primarily in grasslands but including salt gests that at least a small percentage of indi-
marsh (Bedard and LaPointe 1984). Nestling viduals of these species are site faithful while
Savannah Sparrows showed natal philopatry the rest settle with flexible or opportunistic
in New Brunswick island habitats (Wheel- patterns.
wright and Rising 1993). Grasshopper Spar- ACKNOWLEDGMENTS
row return rates varied geographically, being
lower in the Midwest and prairie regions than Lield support and resources were graciously provid-
in the East, with return rates varying between ed by D. M. Prellwitz, Carmen Luna, and the staffat
0 and 52% for migratory populations (Kaspari Bowdoin National Wildlife Refuge. We thank J. E.
Comely and the U.S. Pish and Wildlife Service, Mi-
and O’Leary 1988; Vickery 1996; Balent and
gratory Bird Coordinator's Office in Region 6 for fi-
Norment 2()()3; B. K. Sandercock, pers. nancial and logistical support. We thank the many
comm.). In Connecticut, 50% (/? = 10) of folks who participated with our field efforts, including
those banded in 1986 returned in 1987; in Brice Adams, B. S. Atchley, R. R. Conover, S. K. Da-
Kennebunk, Maine, male return rate was es- vis. R H. Priedman, Micheal Priedrich, G. R. Geupel,
timated at 35% (/? 42) during a 3-year pe- Jeanne Hammond, D. I. Hedegaard, Jessica Hinz, B.
riod; in California, 20% {n — 35) of the adult GK.evLianrsPoany,neR,ebJ.ecMc.aRLuitnhd,, HL.eaBt.heLrinSgaouhlrs,,SC.arNo.liLnuettiSctha,-
males returned (Vickery 1996). Return rates hala, Vicki Trabold, P. N. Wiederrick, andJ. K. Wood.
for Grasshopper Sparrows in the Midwest We are grateful to Merrie Morrison and the American
were lower with 19.8% (// = 111) adult males Bird Conservancy forlogistical supportand B. K. San-
Jones et al. • RETURN RATES OF GRASSLAND SONGBIRDS 93
dercock for use of unpublished data. We thank M. L. iGL, L. D. AND D. H. Johnson. 1999. Ee Conte’s Spar-
Cody, D. H. Johnson, J. M. Ruth, J. A. Sedgwick, N. rows breeding in Conservation Reserve Program
T. Wheelwright, and one anonymous reviewer for fields; precipitation and patterns of population
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sions of this manuscript. Johnson, D. H. and J. W. Grier. 1988. Determinants
of breeding distribution ofducks. Wildlife Mono-
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